CROSS-REFERENCE TO RELATED APPLICATIONS

The present application claims priority to European application No.

17204772.2 filed November 30, 2017, the whole content of this application being incorporated herein by reference for all purposes.

TECHNICAL FIELD

The invention relates to a process for producing a hydroxyapatite composite comprising a hydroxyapatite and at least one activated carbon which is present during synthesis of the hydroxyapatite. It also relates to an adsorbent comprising hydroxyapatite composite for treating effluents contaminated by metals and/or non-metals.

BACKGROUND ART

It is common to treat various sources of water in order to remove contaminants. Examples of sources of water for treatment include surface water, ground water, and industrial aqueous waste streams.

The problems posed by the impact of heavy metals in the environment are well known. Numerous industrial processes release liquid or gaseous effluents that are heavily loaded with heavy metals, in particular heavy metal soluble salts, such as cationic form salts. The expression "heavy metals" is understood to mean metals whose density is at least equal to 5 g/cm ³ , and also beryllium, arsenic, selenium, and antimony, in accordance with the generally accepted definition (Heavy Metals in Wastewater and Sludge Treatment Processes; Vol I, CRC Press Inc; 1987; page 2). Lead or cadmium are particularly significant examples, given their harmful effect on the human body. Nickel is another example thereof due to its allergenic effect.

An example of a problem linked to heavy metals is the combustion of wastes, especially household waste, producing a vaporization of heavy metals, these vapours being entrained in the combustion flue gases. To avoid

contaminating the environment, it is necessary to provide flue gas treatment processes capable of carrying out effective scrubbing of heavy metals. The toxic substances removed from the flue gas when it is purified are found in a residue which itself must often be treated before being reused, repurposed or discharged. Indeed such residue, which contains the heavy metals removed from the flue gas, when subjected, for example, to the action of rain that is acidic when discharged, frequently releases some of the heavy metals that it contains into the

environment. This can then cause pollution of the subsoil. It is therefore essential that the heavy metals be immobilized in the residue.

Wastewater treatment is one of the most important and challenging environmental problems associated with coal-based power generation. Using wet scrubbers to clean flue gas is becoming more popular worldwide in the electrical power industry. While wet scrubbers can greatly reduce air pollution, toxic metals in the resulting wastewater present a major environmental problem. The industry is preparing to invest billions of dollars in the next decade to meet ever more stringent environmental regulations; unfortunately, a cost-effective and reliable technology capable of treating such complicated wastewater is still being sought after.

The compositions of flue gas desulfurization (FGD) wastewaters vary greatly, depending not only on the types of coal and limestone used but also on the types of scrubber and processes used. Pretreatment methods and management practices also affect wastewater characteristics. Untreated raw FDG wastewater could have total suspended solids (TSS) of ~ 10,000 mg/L but after settlement, it falls to ~l0 mg/L; the pH typically ranges from 5.8-7.3; sulfate is in the range of 1,000-6,000 mg/L; nitrate-N at level of 50 mg/L is not uncommon; chloride, alkalinity and acidity vary from hundreds to thousands ppm; selenium (Se) exists in various forms, ranging from dozens of ppb to over 5 ppm, among which, selenate could account for more than half of total Se; arsenic (As) ranges from a few ppb to hundreds of ppb; mercury (Hg) ranges from below 1 ppb to hundreds of ppb; and boron (B) can be as high as hundreds of ppm.

It is particularly desirable to remove selenium from wastewater.

Selenium is a naturally occurring chemical element in rocks, soils, and natural waters. Although Se is an essential micronutrient for plants and animals, it can be toxic at elevated levels and some Se species may be carcinogenic. In water, selenium exists predominately as the inorganic oxyanion forms: selenite (Se0 ₃ ^2- , where the Se is present as the Se ⁴⁺ ion) and selenate (Se0 ₄ ² , where the Se is present as the Se ⁶⁺ ion). Hexavalent selenium is stable in oxic environments and exists as the selenate (Se0 ₄ ² ) anion, which is weakly sorbed by mineral materials and generally soluble. Treatment of selenate in wastewater is often considered to be one of the most difficult anions to remove from water. Tetravalent Se is the stable valence state under mildly reducing or anoxic conditions (0.26 V<Eh<0.55 V at pH 7). Selenite (SeCE ^2- ) anion tends to be bound onto mineral surfaces (e.g., Fe and Mn oxides). Selenate and selenite are more toxic than elemental selenium or metallic selenides due to their high bioavailability.

It is also desirable to remove mercury from wastewater. In particular, the future U.S. EPA guideline for total mercury is <12 part per trillion (ppt) or ng/L. Metal sulfide chemistry is well understood and has been used in various ways in water treatment systems to achieve reduction of dissolved toxic metals from water. For example, organosulfide has been used as a water treatment reagent to precipitate mercury and other toxic metals in the water industry. Iron sulfide materials (FeS or FeS ₂ ores) have been used as adsorbent for toxic metal removal. Conventional sulfide-based toxic metal removal technology has not been able to achieve the desired mercury removal level in many applications. For example, direct application of organosulfide has been found to be unable to achieve mercury removal below 12 ppt in the treated effluent as is required by the new federal or local EPA guidelines.

Heavy metals are not the only priority of the aqueous environment in terms of legislation and environmental impact; regulations also address many organic compounds, such as polycyclic aromatic hydrocarbons (PAHs), phenolic compounds, and pharmaceutical residues. In many industries wastewater such as petrochemical industry, pesticides and insecticides, phenolic compounds posed a big threat to aquatic system due to their toxicity and poor biodegradability.

Petroleum refinery wastewater usually contains high COD due to the presence of polycyclic aromatic hydrocarbons, phenolic compounds and their derivatives.

The United States Environmental Protection Agency and the European Commission have listed PAHs as priority pollutants with the objective of reducing the release of these compounds to the environment. The widespread occurrence of PAHs is largely due to their formation and release in all processes of incomplete combustion of organic materials. PAHs are particularly found in some industrial water originating from heat treatments (such as from incomplete combustion and pyrolysis of fossil fuels or wood and from the release of petroleum products, wet scrubbers or pyrometallurgy process). PAHs are also found in coal tar, crude oil, creosote and roofing tar and a few are used in medicine or to make dyes, plastics, and pesticides. There are thousands of PAH compounds in the environment but in practice PAH analysis is restricted to a few compounds— mostly the 16 priority compounds (Naphthalene, Acenaphthylene, Acenaphthene, Fluorene, Phenanthrene, Anthracene, Fluoranthene, Pyrene, Benz[a]anthracene, Chrysene, Benzo[b] fluoranthene, Benzo[k]fluoranthene, Benzo[a]pyrene, Indeno[l,2,3-cd]pyrene, Dibenzo [a, h] anthracene and

Benzo[ghi]perylene) listed by US EPA as potentially toxic.

Hydroxyapatite is an adsorbent mainly used for trapping and

immobilizing metals within its structure from contaminated effluents, particularly aqueous effluents. Cationic species such as zinc, copper and lead are preferentially trapped over anionic species such as arsenate (As04), selenate (Se04), or molybdate (Mo04). Furthermore, hydroxyapatite does not exhibit a high affinity for mercury despite being in cationic form. As a result, the use of hydroxyapatite cannot be an all-in-one solution for removing the main contaminants from a wastewater effluent to meet the environmental regulations for safe discharge.

There is a need for an adsorbent effective on effluents of industrial origin and also applicable to water purification in general to remove cationic as well as anionic species of contaminating elements.

It is thus useful to develop a material capable of absorbing and retaining large amounts and varieties of contaminants for treating industrial liquid effluents or wastewaters originating from treatment plants before the release thereof into the natural environment, or even the treatment of natural aquifer waters, some of which are naturally loaded with contaminants such as organics (e.g., PAHs, phenolic compounds, naphtol and derivatives) and/or cations and/or oxyanions of metals like Hg and of non-metals, such as As, Se, B.

SUMMARY OF INVENTION

Accordingly, one aspect of the present invention relates to a hydroxyapatite composite which can be effective in trapping simultaneously a large variety of contaminants such as organics (e.g., PAHs, phenolic compounds, naphtol and derivatives) and/or inorganics such as metals and non-metals from a

contaminated effluent. The contaminated effluent may be aqueous, the organic contaminants may be dissolved and/or suspended, and the metal and non-metal contaminants may be in cationic and anionic forms.

To enhance the sorption of the hydroxyapatite towards a larger spectrum of contaminants, it has been found that the hydroxyapatite structure can be supplemented or modified by incorporating at least one activated carbon during the synthesis of the hydroxyapatite to yield a hydroxyapatite composite with an improved adsorption affinity and/or efficiency with respect to at least one contaminant, such adsorption affinity and/or efficiency being greater than that of ae hydroxyapatite structure not containing the activated carbon.

Depending on the physical (size) and chemical forms (treated or not) of the activated carbon which is present during the synthesis of the hydroxyapatite structure (e.g., added prior to the hydroxyapatite synthesis or to a vessel where the hydroxyapatite synthesis takes place), the activated carbon in the

hydroxyapatite composite may be embedded or incorporated into or coated onto the hydroxyapatite structure, or otherwise associated with the hydroxyapatite structure via cohesive forces. Regardless on how the activated carbon is included in the resulting composite, its presence during the hydroxyapatite synthesis results in forming the hydroxyapatite composite.

The hydroxyapatite composite is different than a mere physical mixture of a hydroxyapatite and the activated carbon, which in this case would be made after each material (hydroxyapatite and the activated carbon) would be formed separately and then mixed or blended.

One advantage of embedding or incorporating the activated carbon into the hydroxyapatite during its synthesis is to provide a much more stable material (compared to a mere physical mixture of a hydroxyapatite and the activated carbon) which does not release the activated carbon when in use, particularly in an aqueous solution when the hydroxyapatite composite is intended to perform as adsorbent for removal of contaminants from water.

In preferred embodiments, the activated carbon in the hydroxyapatite composite is a co-sorbent.

The activated carbon is preferably selected based on its own particular affinity and/or efficacy to adsorb or trap at least one contaminant that the hydroxyapatite structure (without activated carbon) does not adsorb or weakly adsorbs. The contaminant may be in the form of organics (e.g., PAHs, phenolic compounds, naphtol and derivatives) and/or inorganics such as a metal or a non- metal in the form of a cation or an oxyanion. For example, the activated carbonmay be selected based on its own particular affinity and/or efficacy to adsorb organics (e.g., PAHs, phenolic compounds, naphtol and derivatives) or mercury such as in the form of mercury cation, selenium such as in the form of its oxyanions (selenate and/or selenite), arsenic such as in the form of its oxyanions (H ₂ As0 ₄ 7HAs0 ₄ ² ) and uncharged H ₃ ASO ₃ form of As(III), and/or boron such in the form of borate. The activated carbon may be further selected based on its ability to increase the porosity of the hydroxyapatite structure. For example, it is preferred that the pore volume and/or the BET surface area of the resulting hydroxyapatite composite synthesized with the activated carbon is higher than that of the hydroxyapatite structure synthesized without the activated carbon.

One advantage of the present invention is improving the sorption affinity of the hydroxyapatite composite for at least one contaminant that would otherwise not be adsorbed or poorly adsorbed from a contaminated effluent by a hydroxyapatite synthesized without the activated carbon. The at least one contaminant may be an organic compound, or a metal or non-metal in the form of a cation or an oxyanion.

Another advantage of the present invention is improving the sorption capacity of the hydroxyapatite composite, for example by increasing its pore volume and/or BET surface area.

When the activated carbon can be used as a sorbent in powder form foriwater treatment, the inclusion of the activated carbon powder as co-sorbent in the hydroxyapatite composite provides yet another advantage. While the use of a co-sorbent in a loose powder offers large surface area and high adsorption capacity, a loose powder needs specific and costly equipment to be removed from treated water effluents, and solid/liquid separation problems limit reactor configurations that require incorporating large sedimentation basins or filtration. There is therefore a benefit for a powdered co-sorbent to be incorporated into the hydroxyapatite structure in accordance to the present invention, so it can be used in practical adsorption processes. The hydroxyapatite synthesis which comprises the presence of the activated carbon powder generates solid particles of larger size than the powder, and these larger particles are easier to separate from a treated water effluent, using a solid/liquid separation technique such as by settling.

One embodiment according to the present invention relates to a

hydroxyapatite composite which comprises:

- a hydroxyapatite; and

at least one activated carbon which is present during the hydroxyapatite synthesis.

The at least one activated carbon may be added to a vessel where hydroxyapatite synthesis takes place, prior to or during the synthesis of the hydroxyapatite. That is to say, when the synthesis of the hydroxyapatite takes place in a vessel, the activated carbon may be added to the vessel before the synthesis is initiated or while the hydroxyapatite structure is synthetized in this vessel.

A particular embodiment according to the present invention relates to a hydroxyapatite composite which comprises:

- a hydroxyapatite; and

at least one activated carbon which increases the porosity of the hydroxyapatite.

The at least one activated carbon is present while the hydroxyapatite structure is synthetized. The at least one activated carbon may be added to the vessel before the synthesis is initiated or while the hydroxyapatite structure is synthetized in this vessel.

The hydroxyapatite composite may have a higher total pore volume and/or a higher BET surface area than a hydroxyapatite material made without the activated carbon.

The hydroxyapatite composite according to the present invention is an effective reactant for immobilizing contaminants from water, in particular when employed in dispersed mode in water treatment units.

The hydroxyapatite composite may comprise at least 50wt%

hydroxyapatite, advantageously at least 60wt%, and more advantageously still at least 70wt% hydroxyapatite or at least 75wt% hydroxyapatite, based on the total weight of dry matter.

In some embodiments, the hydroxyapatite composite may comprise a calcium-deficient hydroxyapatite, preferably with a Ca/P molar ratio more than 1.5 and less than 1.67.

In some embodiments, the hydroxyapatite composite may comprise a calcium-deficient hydroxyapatite and has an overall Ca/P molar ratio higher than the calcium-deficient hydroxyapatite.

The hydroxyapatite composite may further comprise, on the basis of total weight of dry matter,

- water, of the order of from 1 wt% to 30 wt%, advantageously from 2 wt% to 25 wt%, or from 2 wt% to 20 wt%, or from 3 wt% to l5wt% , and/or

- calcium carbonate in an amount of less than 20 wt%, preferably from 1 wt% to 19 wt%, more preferably from 2 wt% to 18 wt%, even preferably from 3 wt% to 15 wt%, yet even more preferably from 4 wt% to 13 wt%, most preferably from 5 wt% to 10 wt%. The hydroxyapatite composite may further comprise, based on the total weight of dry matter, less than 1 wt% of calcium dihydroxide Ca(OH) ₂ , preferably less than 0.5 wt% calcium dihydroxide, more preferably less than 0.3 wt% calcium dihydroxide, even more preferably less than 0.2 wt% calcium dihydroxide, or even less than 0.1 wt% Ca(OH) ₂ ).

The hydroxyapatite composite may comprise a weight ratio of

hydroxyapatite to activated carbon (HAP:AC) of from 1 :0.01 to 1 :0.5, preferably from 1 :0.02 to 1 :0.4 or from 1 :0.03 to 1 :0.4, preferably from 1 :0.04 to 1 :0.3, more preferably from 1 :0.05 to 1 :0.25, yet more preferably from 1 :0.05 to 1 :0.20.

The hydroxyapatite composite may comprise at least 2 wt%, or at least 3 wt%, or at least 4 wt% of the activated carbon based on the total weight of dry matter.

The hydroxyapatite composite may comprise at least 2 wt%, or at least 5 wt% of activated carbon based on the total weight of dry matter. The

hydroxyapatite composite may comprise at most 50 wt%, or at most 40 wt%, or at most 30 wt%, or at most 20 wt% of the activated carbon based on the total weight of dry matter.

The hydroxyapatite composite may further comprise sulfur (S°). The hydroxyapatite composite may comprise at least 2 wt%, or at least 5 wt% of sulfur (S°) based on the total weight of dry matter. The hydroxyapatite composite may comprise at most 40 wt%, or at most 30 wt%, or at most 20 wt% of sulfur (S°) based on the total weight of dry matter. The hydroxyapatite composite may comprise a weight ratio of activated carbon to sulfur (AC:S) of from 10:1 to 1 :10, preferably from 5:1 to 1 :5 or from 3:1 to 1 :3, preferably from 1 :2 to 2:1.

The hydroxyapatite composite may be in the form of particles having a mean size (D50) of at least 20 pm, preferably at least 25 pm, more preferably at least 30 pm.

In additional embodiments, the hydroxyapatite composite may be in the form of particles having a specific surface area of at least 120 m ² /g, preferably of at least 130 m ² /g, more preferably of at least 140 m ² /g.

In additional embodiments, the hydroxyapatite composite may be in the form of particles having a total pore volume of at least 0.3 cm ³ /g, or at least 0.32 cm ³ /g, or at least 0.35 cm ³ /g, or at least 0.4 cm ³ /g.

Another aspect of the present invention relates to a process for producing a hydroxyapatite composite, which may include separate sources of calcium and phosphate or a source of calcium and phosphate and the addition of the additive during the hydroxyapatite synthesis from the separate sources of calcium and phosphate or from the source of calcium and phosphate.

When the process starts with separate sources of calcium and phosphate, the process generally comprises two steps: a reaction of the two sources to obtain a suspension (A) of calcium phosphate, and then an alkaline maturation to form a hydroxyapatite structure.

When the process starts with a source of calcium and phosphate, the process generally comprises an alkaline maturation of the source of calcium and phosphate to form a hydroxyapatite structure.

A preferred embodiment of the process for producing a hydroxyapatite composite according to the present invention comprises:

- in a first step, a source of calcium and a source of phosphate ions are mixed in water in a molar ratio that is adjusted to obtain a Ca/P molar ratio of between 0.5 and 1.6, preferably between 0.7 and 1.3, and reacting the source of calcium with the phosphate ions at a pH of between 2 and 8, in order to obtain a suspension (A) of calcium phosphate,

- in a second step, adding to the suspension (A) an alkaline compound

comprising hydroxide ions in order to set a pH of at least 7.5, preferably at least 8, or at least 8.5, or at least 9, or of at least 10; further adding an additional source of calcium in order to obtain a suspension (B) of composite having a Ca/P molar ratio of greater than 1.6, preferably greater than 1.65, and/or less than 1.75, to form a hydroxyapatite structure; and

- further adding at least one activated carbon in the first step, in the second step, or in both the first and second steps.

The second step may be referred to the“alkaline maturation step”.

When the activated carbon is added in the first step, it may be added at the beginning of the first step before the reaction between the source of calcium with the phosphate ions takes place, during the reaction, or after the reaction is completed in the first step (this being preferred).

In some embodiments, the activated carbon may be added more than once, for example in at least two portions, for example a first portion in the first step and a second portion in the second step.

In some embodiments, two or more activated carbons may be added. In an example, an activated carbon may be added in the first step and a second activated carbon may be added in the second step. Alternatively, two or more activated carbons may be added in the first step or in the second step.

The first step and the second step where hydroxyapatite synthesis takes place may be carried out in a same vessel (preferably), but not necessarily.

An alternate embodiment of the alternate process for producing the hydroxyapatite composite comprises the following steps:

- forming an aqueous suspension comprising particles of a calcium phosphate compound having a Ca/P molar ratio of 1.5 or less, preferably between 0.50 and 1.35, more preferably particles containing brushite, yet more preferably particles containing >70 wt% brushite, most preferably particles containing >90 wt% brushite;

- adding an alkaline compound comprising calcium and hydroxide ions in order to increase the pH of the suspension to a value of at least 6.5, preferably at least 7, or at least 7.5, or at least 8, or of at most 11 in order to obtain a suspension (B’) having a Ca/P molar ratio of greater than 1.6, preferably greater than 1.65, and/or less than 1.75; and

- further adding at least one activated carbon to the suspension (B’) before, during or after the addition of the alkaline compound, preferably before or during the addition of the alkaline compound, to form the hydroxyapatite composite,

wherein said suspension (B’) contains from 10 to 35 wt% solids, preferably from 15 to 25 wt% solids.

In preferred embodiments, the alkaline compound comprises calcium hydroxide.

The steps of addition of the alkaline compound comprising calcium and hydroxide ions is preferably carried out at a temperature of more than 40°C, or of at least 50°C, or of at least 60°C), and/or less than 90°C.

The activated carbon in the hydroxyapatite composite may be incorporated or embedded into or coated onto the hydroxyapatite structure, or otherwise associated with the hydroxyapatite structure via cohesive forces.

Furthermore, the hydroxyapatite composite generated by this method is different than a mere physical mixture of the activated carbon with a

hydroxyapatite material made using the same method but without the activated carbon, in that the activated carbon in the hydroxyapatite composite is not released from the hydroxyapatite structure when agitated in deionized water for at least 5 hours. The composite may be organic or inorganic, preferably inorganic.

In some optional embodiments, another optional additive may be included in the synthesis of the composite. In addition to the activated carbon, the other additive may comprise chitosan, hopcalite, clays (e.g., bentonite), zeolites, sulfur, a metal in the form of metal of oxidation state 0, salt, oxide,

oxyhydroxide, or hydroxide and being selected from the group consisting of aluminium, tin, at least one transition metal selected from Groups 3-12 of the June 2016 IUPAC Periodic Table of Elements , in particular iron (in the form of metal of oxidation state 0, salt, oxide, oxyhydroxide, or hydroxide), or combinations of two or more thereof.

In some optional embodiments, the other optional additive may comprise a transition metal in the form of metal of oxidation state 0, salt, oxide,

oxyhydroxide, or hydroxide. The transition metal is preferably selected from the group consisting of iron, titanium, nickel, copper, zinc, zirconium, lanthanum, and cerium, more preferably selected from the group consisting of iron, nickel, copper, zinc, and lanthanum; yet more preferably selected from the group consisting of iron, nickel, and copper. In most preferred embodiments, the other additive may comprise iron in the form of metal of oxidation state 0, salt, oxide, oxyhydroxide, or hydroxide.

In some embodiments, the composite may comprise at least one activated carbon, and an optional additive selected from: chitosan, hopcalite, iron (which may be in the form of metal of oxidation state 0, salt, oxide, oxyhydroxide, or hydroxide, preferably oxyhydroxide or hydroxide), or combinations of two or more thereof.

In some embodiments, the composite may comprise at least one activated carbon and sulfur (zero-valent S) as an optional additive.

In some embodiments, the optional additive may comprise aluminium (in the form of metal, salt, oxide, oxyhydroxide, or hydroxide), tin (in the form of metal, salt, oxide, oxyhydroxide, or hydroxide), at least one transition metal selected from Groups 3-12 of the IUPAC Periodic Table of Elements (June 2016) (in the form of metal of oxidation state 0, salt, oxide, oxyhydroxide, or hydroxide), preferably selected from the group consisting of iron, titanium, nickel, copper, zinc, zirconium, lanthanum, and cerium; most preferably may be iron in the form of metal of oxidation state 0, salt, oxide, oxyhydroxide, or hydroxide; clays (e.g., bentonite); zeolites; or combinations of two or more thereof. Suitable optional additives or precursors thereof that may be added in the first step in the two-step process include compounds that are stable / compatible under acidic conditions, such as a pH<6.5, or pH<6. Examples of optional additives or precursors thereof that may be added in the first step are activated carbon and/or chloride salts of the following metals: aluminium, tin, or a transition metal of groups 3-12 of the June 2016 IUPAC Periodic Table, preferably titanium, iron, nickel, copper, zinc, zirconium, lanthanum, and/or cerium; more preferably iron, nickel, copper, and/or lanthanum).

Moreover the hydroxyapatite composite according to the invention, when made in the first step at low temperature (less than 40°C, preferably 20-25°C), and the (second) alkaline maturation step made at higher temperature (more than 40°C, or of at least 50°C, or of at least 60°C), has shown particularly high specific surface (at least 120 m ² /g, or at least 130 m ² /g, or at least 140 m ² /g) and particular high adsorption capacity of metals such as Hg or its cations, and non- metals such as Se, As, and/or B or their respective oxyanions.

In some embodiments according to the present invention, the

hydroxyapatite composite is in the form of particles that comprise plate-like crystallites, of thickness of a few nano-meters (nm) on their surface, which are coated by smaller particles of the activated carbon. The smaller particles of the activated carbon are likely associated with the hydroxyapatite structure via cohesive forces.

In some embodiments according to the present invention, the

hydroxyapatite composite particles may comprise two distinct types of solid particles, a first type associated with the hydroxyapatite structure with plate-like crystallites, of thickness of a few nano-meters (nm) on their surface, and another type of particles associated with the activated carbon. These distinct types of solid particles are preferably interdispersed. Because the activated carbon is added prior to or during the synthesis of the hydroxyapatite structure, the particles associated with the activated carbon are linked to the first type of particles associated with the hydroxyapatite structure via cohesive forces, because they are not released from the composite after being submerged under agitation in deionized water for at least 5 hours.

Another aspect of the present invention further relates to an adsorbent material for removal of contaminants from water, comprising or consisting of: - an hydroxyapatite composite comprising at least an activated carbon according to the invention; or - two or more hydroxyapatite composites according to the invention, wherein the activated carbons in the hydroxyapatite composites are different; preferably wherein at least one of the hydroxyapatite composites comprising an activated carbon further comprises an optional additive as provided herein; or

- a blend of a hydroxyapatite without activated carbon and at least one hydroxyapatite composite comprising at least one activated carbon according to the invention.

Another aspect of the present invention relates to the use of the

hydroxyapatite composite according to the present invention or of the adsorbent material according to the present invention for purifying a substance comprising one or more contaminants such as a water or gas effluent, or for removing at least a portion of one or more contaminants from a water or gas effluent, preferably from a water effluent, particularly removing cations such as Hg cations, and/or oxyanions such as those of Se, As and/or B from a water effluent, comprising using the hydroxyapatite composite according to the present invention or of the adsorbent material according to the present invention.

Another aspect of the present invention relates to a method for purifying a contaminated substance comprising one or more contaminants such as a water or gas effluent, or for removing at least a portion of one or more contaminants from a water or gas effluent, preferably from a water effluent, particularly removing cations such as Hg cations, and/or oxyanions such as those of Se, As and/or B from a water effluent, comprising using the hydroxyapatite composite according to the present invention or of the adsorbent material according to the present invention.

The use or the method for purifying or removing one or more contaminants preferably comprises contacting the hydroxyapatite composite or the adsorbent material with the contaminated substance or effluent to remove at least a portion of the one or more contaminants.

BRIEF DESCRIPTION OF FIGURES FIG. 1 is a diagram of the two-step method for preparing the hydroxyapatite composite, where the activated carbon is added in the“alkaline maturation” step while the hydroxyapatite structure is formed.

FIG. 2 illustrates the release of activated carbon from a physical mixture of activated carbon and hydroxyapatite particles made without additive (not according to the invention) compared to the hydroxyapatite composite (according to the invention) which showed little release of activated carbon after agitation in deionized water for 5 hours.

FIG. 3 is a scanning electron microscope (SEM) picture at magnification of 500 of a particulate hydroxyapatite made according to the same method used for making the hydroxyapatite composite according to the present invention, except that no additive is added during the hydroxyapatite synthesis (not according to the invention).

FIG. 4 is a scanning electron microscope (SEM) picture at magnification of 500 of a particulate hydroxyapatite composite comprising activated carbon as the additive (according to the invention).

DEFINITIONS

Unless otherwise specified, all reference to percentage (%) herein refers to percent by weight.

“Fresh” material or sorbent denotes a material which has not been in contact with contaminants, whereas“spent” catalyst denotes a material which has already been in contact with contaminants.

As used herein, the term“upstream” refers to a position situated in the opposite direction from that in which the gas stream to be treated flows.

As used herein, the term“downstream” refers to a position situated in the same direction from that in which the gas stream to be treated flows.

As used herein, the terms“% by weight”,“wt%”,“wt. %”,“weight percentage”, or“percentage by weight” are used interchangeably.

As used herein, the term“dry matter” refers to a material which has been subjected to drying at a temperature of l05°C for at least 1 hour.

As used herein, the BET specific surface area is determined by gas adsorption on a Micromeritics ASAP2020 machine. The measurement is carried out using nitrogen as adsorbent gas at 77°K via the volumetric method, according to the ISO 9277 : 2010 standard (Determination of the specific surface area of solids by gas adsorption - BET method). The BET specific surface area is calculated in a relative pressure (R/R0) range varying from around 0.05 to 0.20.

In the present specification, the choice of an element from a group of elements also explicitly describes :

- the choice of two or the choice of several elements from the group,

- the choice of an element from a subgroup of elements consisting of the group of elements from which one or more elements have been removed.

In addition, it should be understood that the elements and/or the characteristics of a composition, a method, a process or a use, described in the present specification, can be combined in all ways possible with the other elements and/or characteristics of the composition, method, process, or use, explicitly or implicitly, this being without departing from the context of the present specification.

In the passages of the present specification that will follow, various embodiments or items of implementation are defined in greater detail. Each embodiment or item of implementation thus defined can be combined with another embodiment or with another item of implementation, this being for each mode or item unless otherwise indicated or clearly incompatible when the range of the same parameter of value is not connected. In particular, any variant indicated as being preferred or advantageous can be combined with another variant or with the other variants indicated as being preferred or advantageous.

In the present specification, the description of a range of values for a variable, defined by a bottom limit, or a top limit, or by a bottom limit and a top limit, also comprises the embodiments in which the variable is chosen, respectively, within the value range : excluding the bottom limit, or excluding the top limit, or excluding the bottom limit and the top limit.

In the present specification, the description of several successive ranges of values for the same variable also comprises the description of embodiments where the variable is chosen in any other intermediate range included in the successive ranges. Thus, for example, when it is indicated that "the magnitude X is generally at least 10, advantageously at least 15", the present description also describes the embodiment where : "the magnitude X is at least 11", or also the embodiment where : "the magnitude X is at least 13.74", etc.; 11 or 13.74 being values included between 10 and 15.

The term "comprising" includes "consisting essentially of' and also "consisting of'.

In the present specification, the use of "a" in the singular also comprises the plural ("some"), and vice versa, unless the context clearly indicates the contrary. By way of example, "a mineral" denotes one mineral or more than one mineral.

If the term "approximately" or“about” is used before a quantitative value, this corresponds to a variation of ± 10 % of the nominal quantitative value, unless otherwise indicated. DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

One embodiment according to the present invention relates to a

hydroxyapatite composite which comprises:

a hydroxyapatite; and

at least one activated carbon which is present during the hydroxyapatite synthesis.

The hydroxyapatite composite may have a higher total pore volume and/or a higher BET surface area than a hydroxyapatite material made without the activated carbon.

A particular embodiment according to the present invention relates to a hydroxyapatite composite which comprises:

a hydroxyapatite; and

at least one activated carbon which increases the porosity of the hydroxyapatite.

The at least one activated carbon may be added prior to or during the hydroxyapatite synthesis.

With respect to the increases in porosity of the hydroxyapatite, the composite material preferably has a higher total pore volume than a

hydroxyapatite material made without the activated carbon.

With respect to the increases in porosity of the hydroxyapatite, the composite material preferably has a higher BET surface area than a

hydroxyapatite material made without the activated carbon.

The hydroxyapatite composite is different than a physical mixture of the activated carbon with a hydroxyapatite material made without the activated carbon. The activated carbon in the hydroxyapatite composite is not released from the hydroxyapatite structure when agitated in deionized water for at least 5 hours.

ACTIVATED CARBON:

The activated carbon in the composite may originate from various sources. It can be produced from carbonaceous source materials such as bamboo, coconut husk/shell, willow peat, wood, coir, lignite, coal, petroleum coke,

and/or petroleum pitch.

In preferred embodiments, the activated carbon in the composite may be added in a powder form. Its average particle size is generally in size of less than 1 mm. Preferred average particle size for activated carbon may be at most 500 microns, preferably at most 400 microns, or at most 300 microns, or at most 200 microns, or at most 100 microns, or at most 80 microns, or at most 60 microns. Generally, the average particle size for activated carbon may be at least 5 microns, or at least 10 microns.

In particular embodiments, the average particle size for activated carbon is preferably within +/- 50% of the average particle size of the hydroxyapatite which is to be synthesized in the presence of this activated carbon.

In particular preferred embodiments, the average particle size for activated carbon is preferably less than the average particle size of the hydroxyapatite which is to be synthesized in the presence of this activated carbon.

The activated carbon may be selected based at least on the following criteria: the activated carbon yields a pH of at least 5 when dispersed in a suspension at 0.3 wt% in deionized water for 5 hours.

When the composite comprises an activated carbon or blend of two or more activated carbons, the activated carbon or blend of two or more activated carbons is selected so that a 0.3 wt% dispersion of the activated carbon(s) in deionized water provides a pH of 5 or more.

If the selected activated carbon yields a pH of less than 5 when dispersed in a suspension at 0.3 wt% in deionized water for 5 hours, then a blend with another more-alkaline activated carbon may be used in the composite to provide a pH of 5 or more.

The activated carbon may comprise a pore volume of at least 0.25 cm ³ /g, preferably at least 0.35 cm ³ /g, more preferably at least 0.4 cm ³ /g.

The activated carbon may have a BET surface are of at least 500 m ² /g, preferably at least 750 m ² /g.

The activated carbon may have a unique distribution of pore sizes that contributes to the ability of the composite to remove specific contaminants from aqueous systems. In one embodiment, the activated carbon has a porosity of at least about 0.25 cm ³ /g. The pores diameter of the activated carbon may be at least about 10 and at most about 500 A (Hg intrusion porosimetry, such as using a Micromeritics model AutoPore-II 9220 porosimeter). In another embodiment, the activated carbon has a porosity of at least about 0.4 cm ³ /g in pores diameter of at least about 10 and at most about 500 A.

In some embodiments, the activated carbon has been subjected to a treatment prior to being used into the hydroxyapatite composite synthesis. Such treatment may enhance the sorption capability of the activated carbon and/or modify the porosity of the activated carbon. For example the activated carbon may be impregnated by sulfur to enhance the sorption of mercury cations. An example of such sulfur- impregnated activated carbon is MerSorb® from NUCON International.

In another treatment example, the activated carbon may be subjected to an acid treatment such as with nitric acid.

Yet in another treatment example, the activated carbon may be subjected to steam, generally to impact its porosity.

In some embodiments, the activated carbon is not treated with acid prior to being used into the hydroxyapatite composite synthesis.

In some embodiments, the activated carbon may be in the form of a solid before it is added to at least one of the first and (second) alkaline maturation steps of the two-step process of making the composite.

In some embodiments, the activated carbon may be in the form of a solid before it is added at the beginning or during the alkaline maturation step of the process for making the composite.

In some embodiments, when the D50 particle size of the solid activated carbon is greater than 100 microns may further include grinding or milling the solid to achieve a D50 less than 100 microns or less than 90 microns, preferably less than 75 microns, or more preferably less than 63 microns, before the resulting powder is added to at least one of the first and second steps of the method of making the composite.

In some embodiments, when the activated carbon may be in the form of a powder (either sold‘as is’ or ground before use), the powder of the activated carbon may be sieved to remove large particles, such as those exceeding a size of 100 microns, or exceeding a size of 90 microns. For example, the powder of the activated carbon which passes through a sieve No. 170 (under ASTM El l) equivalent to a size of less than 90 microns, or through a sieve No. 200 (under ASTM El l) equivalent to a size of less than 75 microns, or through a sieve No. 230 (under ASTM El 1) equivalent to a size of less than 63 microns can be added to at least one of the first and second steps of the two-step process of making the composite, or at the beginning or during the alkaline maturation step of the one- step or two-step process for making the composite. OPTIONAL ADDITIVE:

In some embodiments, the composite further comprises an optional additive. The optional additive or a precursor thereof is preferably present or formed during the synthesis of the hydroxyapatite. The hydroxyapatite composite may comprise more than one optional additive.

When the composite comprises an optional additive, the activated carbon may serve as support for the optional additive.

The hydroxyapatite composite may comprise more than one optional additive. In such embodiments, a first optional additive may serve as support for a second optional additive.

The optional additive may comprise chitosan, hopcalite, clays (e.g., bentonite), zeolites, sulfur, and/or a metal in the form of metal of oxidation state 0, salt, oxide, oxyhydroxide, or hydroxide being selected from the group consisting of aluminium, tin, a transition metal selected from Groups 3-12 of the June 2016 IUPAC Periodic Table of Elements, and combinations of two or more thereof, preferably selected from the group consisting of aluminium, tin, titanium, iron, nickel, copper, zinc, zirconium, lanthanum, cerium, and any combination thereof; more preferably being selected from the group consisting of aluminium, tin, iron, nickel, copper, zinc, lanthanum, and any combination thereof.

In some embodiments, the hydroxyapatite composite may comprise at least one activated carbon as a first additive and a metal in the form of zero-valent metal, salt, oxide, oxyhydroxide, or hydroxide as an second additive, wherein the metal may be selected from the group consisting of aluminium, tin, a transition metal selected from Groups 3-12 of the June 2016 IUPAC Periodic Table of

Elements, preferably selected from the group consisting of aluminium, tin, titanium, iron, nickel, copper, zinc, zirconium, lanthanum, cerium, and any combination thereof; more preferably selected from the group consisting of aluminium, tin, iron, nickel, copper, zinc, lanthanum, and any combination thereof.

When an optional additive comprises a zeolite, the additive preferably comprises a zeolite selected from the group consisting of ZSM-5 (MFI), faujasites such as X, Y, US-Y, mordenites, chabazite, clinoptilolite, beta-zeolites such as 3 A, 4A, 5 A, and any combination thereof. The zeolite may be a high silica zeolite with a Si/Al molar ratio greater than 5, such as ZSM-5 (MFI), beta- zeolites such as 3 A, 4A, 5 A, or combinations thereof. The zeolite may be an intermediate silica zeolite with a Si/Al molar ratio from 2 to 5, such as chabazite, a faujasite, a mordenite, or combinations thereof.

When an optional additive comprises a clay, the additive may comprise kaolinite, antigonite, berthierines, pyrophyllite, talc, montmorillonite, hectorite, beidellite, saponite, illites, vermiculites, muscovite, phlogopite, margarite, clintonite, sepiolite, bentonite, attapulgite, diatomacous earth, or any

combinations thereof; more preferably comprises a clay selected from the group consisting of kaolinite, montmorillonite, vermiculite, bentonite, and any combination thereof.

The optional additive may be organic or inorganic.

In preferred embodiments, the optional additive is inorganic. The optional additive preferably comprises hopcalite, aluminium, tin, sulfur, and/or a transition metal selected from Groups 3-12 of the June 2016 IUPAC Periodic Table of Elements, such as titanium, iron, copper, nickel, zirconium, lanthanum, cerium, etc . each metal being in the form of metal of oxidation state 0, salt, oxide, oxihydroxide, or hydroxide.

In such instance, the optional additive may comprise hopcalite, iron (in the form of metal, salt, oxide, oxyhydroxide, or hydroxide), aluminium (in the form of metal, salt, oxide, oxyhydroxide, or hydroxide), or combinations of two or more thereof.

In some embodiments, an optional additive may comprise or consist of hopcalite.

The hopcalite is a mixture of manganese oxide and copper oxide, which has been used for the capture of mercury in gaseous effluents. A synthesis method is described in the publication of T. J. Clarke, S. A. Kondrat, S. H.

Taylor, Total oxidation of naphtalene using copper manganese oxide catalyst. Catalysis Today vol 258 (2015) pp. 610-615.

In some embodiments, an optional additive may comprise or consist of an iron-containing additive, preferably in the form of metal of oxidation state 0, salt, oxide, oxyhydroxide, or hydroxide, preferably in the form of metal of oxidation state 0, oxide, oxyhydroxide, or hydroxide. The iron in the additive may be of oxidation state 0, 2 or 3. The iron-containing additive is preferably inorganic. If the additive comprises an iron salt, the iron salt is preferably inorganic.

The optional additive may comprise or consist of an iron oxide. The iron oxide may be iron(III) oxide or ferric oxide of formula Fe ₂ 0 ₃ , iron(II) oxide (FeO), or ΐtoh(II,III) oxide (Fe ₃ 0 ₄ ). The additive may comprise or consist of Fe30 ₄ . Fc ₃ 0 ₄ can occur naturally as the mineral magnetite or may be

synthesized, for example in the form of nanoparticles. Examples of synthesis of Fe ₃ 0 ₄ nanoparticles can be found in Gonzales et ah, 2012, Journal of Hazard Materials, vol. 211-212, pg. 138-145 using non microwave-assisted or microwave-assisted synthetic techniques or using chemical co -precipitation method similar to previously described in Onar & Yakinci, Journal of Physics: Conference Series 667 (2016) 012005, the International Conference on Magnetic and Superconducting Materials (MSM15), IOP Publishing doi: 10.1088/1742- 6596/667/1/012005, and Meng et al, Applied Surface Science, Vol.280, pg. 679- 685.

When the optional additive comprises iron, the additive more preferably comprises iron(III) hydroxide, and/or iron(III) oxyhydroxide; more preferably comprises iron(III) oxyhydroxide.

Iron(III) hydroxide has the chemical formula Fe(OH)3.

Iron(III) oxyhydroxide has the chemical formula FeOOH. It can be obtained for example by reacting ferric chloride with sodium hydroxide.

Alternatively, iron(II) may be oxidized to iron(III) by hydrogen peroxide in the presence of an acid. Furthermore, ferric hydroxide can be prepared as described in W02003/053560 or can be prepared as described in [0045] of

W02017/109014 using solution of Fc/NOA and acetic acid and solution of ammonia. Alternatively, commercially available iron(III) oxide-hydroxide may be used. Iron(III) oxide-hydroxide occurs in anhydrous and hydrated forms. Ferrihydrite (FeOOH ^» 0.4H ₂ O) is a hydrous ferric oxyhydroxide mineral which is also suitable for use as additive. Furthermore, iron(III) oxyhydroxide occurs in four different polymorphic forms, known as alpha-, beta-, gamma- and delta- FeOOH. All these forms may be used in the present invention. Goethite is a widespread mineral of formula -FeO(OH) and lepidocrocite is a less common mineral of formula y-FeO(OH) with the same chemical composition as goethite but with a different crystal structure.

The iron(III) oxyhydroxide particles may have a median particle size in the range of from about 1 to about 3,000 nm, preferably about 5 to about 2,000 nm, more preferably from about 10 to about 700 nm, even more preferably from about 50 to about 500 nm, such as in the range of from about 100 to about 400 nm. The iron(III) oxyhydroxide may be formed in situ during the synthesis of the hydroxyapatite by adding the Fe precursor and adding a base to form the

FeOOH, or FeOOH may be added as an aqueous slurry or solution comprising from at least 1 wt% to at most 20 wt% FeOOH, or from at least 2 wt% to at most 15 wt% FeOOH, or from at least 2 wt% to at most 10 wt% FeOOH.

The iron may be added during the synthesis of the hydroxyapatite in the form of an iron precursor such as a salt. A suitable precursor of iron may be iron chloride, iron nitrate, iron sulfate, or any combination thereof. A base (source of OH ) is generally added to this iron precursor to generate iron(III) hydroxide or oxyhydroxide.

When the optional additive comprises aluminium, the aluminium- containing additive preferably is in the form of metal (oxidation state 0), salt, oxide, oxyhydroxide, or hydroxide; more preferably in the form of oxide, oxyhydroxide, or hydroxide; yet more preferably in the form of oxyhydroxide or hydroxide. The aluminium-containing additive is preferably inorganic. The aluminium salt is preferably inorganic.

The aluminium- containing optional additive may be in the form of boehmite or pseudoboehmite, bauxite, gibbsite including the bayerite form, and/or alumina (from g-alumina to a- alumina, also known as

‘corundum’). Boehmite has the chemical formula g-AIO(OH), and gibbsite has the chemical formula g-A1(OH) ₃ . A pseudo-boehmite refers to a monohydrate of alumina having a crystal structure corresponding to that of boehmite but having low crystallinity or ultrafine particle size.

In some embodiments, the aluminium- containing optional additive may comprise or be a hydrated aluminium oxide (e.g., g-alumina) also called‘hydrous aluminium oxide’, for example in the form of an amorphous aluminium hydroxide phase such as bayerite.

When the optional additive comprises tin, the tin-containing optional additive may be in the form of zero-valent metal, salt, oxide, oxyhydroxide, or hydroxide, preferably tin (II) oxyhydroxide or tin(II) oxide. An example of a suitable tin-containing optional additive may comprise or consist of Sn(II) oxyhydroxide and/or Sn0 ₂ , that can be effective in Cr(VI) and Cr(III) removal from water - see Pinakidou et ah, Science of the Total Environment, vol 551-552 (2016) pp. 246-253.

When the optional additive comprises lanthanum, the lanthanum- containing optional additive may be in the form of metal, salt, oxide,

oxyhydroxide, or hydroxide, preferably lanthanum(III) hydroxide or

oxyhydroxide. Crystals of lanthanum oxyhydroxide (LaOOH) can be made using an electrochemical method (Samata H., Journal of Crystal Growth, Vol. 304(2), 2007, pp. 448-451).

The optional additive may comprise or consist of chitosan. Chitosan is a linear polysaccharide composed of randomly distributed b-( 1 4)-linkcd D- glucosamine (deacetylated unit) and /V-acctyl-D-glucosaminc (acetylated unit). It is made by treating the chitin shells of shrimp and other crustaceans with an alkaline substance, like sodium hydroxide.

In some embodiments, the composite may exclude a polymer, such as may exclude chitosan and/or polyvinyl alcohol.

In some embodiments, the optional additive may comprise or consists of a clay. When the optional additive comprises a clay, the optional additive preferably comprises kaolinite, antigonite, berthierines, pyrophyllite, talc, montmorillonite, hectorite, beidellite, saponite, illites, vermiculites, muscovite, phlogopite, margarite, clintonite, sepiolite, bentonite, attapulgite, diatomacous earth, or any combinations thereof; more preferably comprises kaolinite, montmorillonite, vermiculites, bentonite, or any combinations thereof. TABLE 1 provides below the chemical formula with key characteristics of suitable clays.

In some embodiment, the clay may be subjected to an acid treatment to make an acidified clay prior to being used to synthetize the hydroxyapatite composite.

In some embodiments, the composite may exclude a clay, such as may exclude an acidified clay.

TABLE 1 - Clays suitable for additive in the composite

In some embodiments, the optional additive may comprise or consists of at least one zeolite.

When the optional additive comprises a zeolite, the additive preferably comprises a zeolite selected from the group consisting of ZSM-5 (MFI), faujasites such as X, Y, US-Y, mordenites, chabazite, clinoptilolite, beta-zeolites such as 3A, 4A, 5 A, and any combination thereof. The zeolite may be a high silica zeolite with a Si/Al molar ratio greater than 5, such as ZSM-5 (MFI), beta- zeolites such as 3 A, 4A, 5 A, or combinations thereof. The zeolite may be an intermediate silica zeolite with a Si/Al molar ratio from 2 to 5, such as chabazite, a faujasite, a mordenite, or combinations thereof.

In some embodiments, the composite may exclude a zeolite.

In some embodiments, the composite may comprise at least one activated carbon and sulfur (zero-valent S) as an optional additive. PARTICLE SIZE OF COMPOSITE:

The hydroxyapatite composite comprises solid particles with a mean diameter D50 of which is greater than 10 pm, in general greater than 20 pm, or even greater than 25 pm, or even at least 30 pm, or even at least 35 pm, and/or preferably less than 200 pm, or even less than 150 pm, or even less than 100 pm. In some preferred embodiments, the hydroxyapatite composite comprises solid particles with a mean diameter D50 from 20 microns to 60 microns, or from 25 microns to 60 microns, or from 30 microns to 60 microns. The mean diameter in question is the D50, that is to say the diameter such that 50 % by weight of the particles have a diameter less than said value.

The mean particles size D50 is the diameter such that 50 % by weight of the particles have a diameter less than said value. The particle size measurement may be measured using laser diffraction, such as using a Beckman Coulter LS 230 laser diffraction particle size analyser (laser of wavelength 750 nm) on particles suspended in water and using a size distribution calculation based on Fraunhofer diffraction theory (particles greater than 10 pm) and on Mie scattering theory (particles less than 10 pm), the particles being considered to be spherical.

COMPOSITION OF COMPOSITE

The hydroxyapatite composite according to the invention in general comprises at least 50wt% hydroxyapatite, advantageously at least 60wt% or advantageously still at least 70wt% hydroxyapatite, still more advantageously at least 75wt% hydroxyapatite, based on the total weight of dry matter.

The hydroxyapatite composite preferably comprises a weight ratio of hydroxyapatite to activated carbon (HAP:AC) of from 1 :0.0l to 1 :0.5. That is to say, when lOOg of hydroxyapatite in the composite, a minimum of 1 g of activated carbon is present and/or a maximum of 50 g is present in the composite. The weight ratio of is preferably at least 1 :0.02 or at least 1 :0.03.

The weight ratio of is preferably at most 1 :0.3, more preferably at most 1 :0.25. The hydroxyapatite composite may comprise a weight ratio of hydroxyapatite to activated carbon (HAP:AC) of from 1 :0.01 to 1 :0.5, preferably from 1 :0.02 to 1 :0.4 or from 1 :0.03 to 1 :0.4, more preferably from 1 :0.04 to 1 :0.3, yet more preferably from 1 :0.05 to 1 :0.25, yet even more preferably from 1 :0.05 to 1 :0.20.

A range of 5 to 20 g activated carbon per 100 g of hydroxyapatite is particularly suitable. The hydroxyapatite composite may further comprise: water, of the order of from 0 to 20 wt%, advantageously from 1 % to 20 wt%, more advantageously from 2 % to 10 wt%, based on the total weight of dry matter.

In some embodiments, the hydroxyapatite composite may comprise water, of the order of from 5 wt% to 20 wt%, advantageously from 6 wt% to 20 wt%, based on the total weight of dry matter.

In some embodiments, the hydroxyapatite composite may comprise, based on the total weight of dry matter, less than 5 wt% water, preferably less than 5 wt% and down to 0.1 wt% or even lower

In some embodiments, the hydroxyapatite composite may further comprise, based on the total weight of dry matter, calcium carbonate in an amount of less than 20 wt% and more than 0 wt%, preferably from 1 wt% to 19 wt%, more preferably from 2 wt% to 18 wt%, even more preferably from 5 wt% to 15 wt%, yet even more preferably from 7 wt% to 13 wt%, most preferably from 8 wt% to 12 wt%.

The hydroxyapatite composite may further comprise, based on the total weight of dry matter, calcium dihydroxide Ca(OH) ₂ from 0 to 20 %,

advantageously from 0 to 4 %, or more advantageously from 0 to 1 wt%, or alternatively more than 0 wt% but at most 4 wt%, or from 1% to 4wt%.

In some embodiments, the hydroxyapatite composite may comprise less than 1 wt% of calcium dihydroxide Ca(OH) ₂ , preferably less than 0.5 wt% calcium dihydroxide, more preferably less than 0.3 wt% calcium dihydroxide, even more preferably less than 0.2 wt% calcium dihydroxide. In some embodiments, the porous support is substantially free of calcium dihydroxide (i.e., less than 0.1 wt% Ca(OH) ₂ ).

In some embodiments, the hydroxyapatite composite may comprise at least 2 wt%, preferably at least 2.5 wt% or at least 3 wt%, more preferably at least 5 wt%, and yet more preferably at least 6 wt% of hydroxide ions.

The particles of hydroxyapatite composite may additionally contain residual compounds originating from the use of the raw materials in the process such as: CaCl ₂ , Ca(N0 ₃ ) ₂ , sands or clays; these residual constituents are in general less than 5% by weight, advantageously less than 2% by weight based on the total weight of dry matter.

In some embodiments, the hydroxyapatite composite may comprise, on the basis of the total weight of dry matter, - water, of the order of from 1 wt% to 20 wt%, advantageously from 2 wt% to 20 wt%, or from 2 wt% to 10 wt%, or from 3 wt% to 8 wt%, and/or

- calcium carbonate in an amount of less than 20 wt% and more than 0 wt%, preferably from 1 wt% to 19 wt%, more preferably from 2 wt% to 18 wt%, even preferably from 3 wt% to 15 wt%, yet even more preferably from 4 wt% to 13 wt%, most preferably from 5 wt% to 10 wt%.

The hydroxyapatite composite may further comprise, based on the total weight of dry matter, less than 1 wt% of calcium dihydroxide Ca(OH) ₂ , preferably less than 0.5 wt% calcium dihydroxide, more preferably less than 0.3 wt% calcium dihydroxide, even more preferably less than 0.2 wt% calcium dihydroxide, or even less than 0.1 wt% Ca(OH) ₂ ).

The hydroxyapatite composite may comprise a calcium-deficient hydroxyapatite, preferably with a Ca/P molar ratio more than 1.5 and less than 1.67.

The hydroxyapatite composite may comprise a calcium-deficient hydroxyapatite and has an overall Ca/P molar ratio higher than the calcium- deficient hydroxyapatite.

In preferred embodiments, the hydroxyapatite composite may comprise activated carbon for example in an amount of at least 5 wt% activated carbon but in an amount of at most 20 wt% activated carbon.

In some preferred embodiments, the hydroxyapatite composite is substantially free of bone char.

In preferred embodiments, the hydroxyapatite composite excludes bone char.

In preferred embodiments, the hydroxyapatite composite does not contain an organic polymer crosslinked network, for example created by in-situ polymerization of at least one polymer during the synthesis of the hydroxyapatite composite.

In some embodiments, the hydroxyapatite composite may exclude a polymer, such as may exclude chitosan and/or a polyvinyl alcohol.

In preferred embodiments, the hydroxyapatite composite is inorganic.

In other embodiments, the hydroxyapatite composite contains less than 1 wt% organics.

When the hydroxyapatite composite comprises an optional additive, it preferably comprises a weight ratio of hydroxyapatite to optional additive

(HAP:A) of from 1 :0.01 to 1 :0.5. That is to say, when lOOg of hydroxyapatite in the composite, a minimum of 1 g of optional additive is present and/or a maximum of 50 g is present in the composite. The weight ratio of is preferably at least 1 :0.02 or at least 1 :0.03. The weight ratio of is preferably at most 1 :0.3, more preferably at most 1 : 0.25. The hydroxyapatite composite may comprise a weight ratio of hydroxyapatite to optional additive (HAP:A) of from 1 :0.0l to 1 :0.5, preferably from 1 :0.02 to 1 :0.4 or from 1 :0.03 to 1 :0.4, more preferably from 1 :0.04 to 1 :0.3, yet more preferably from 1 :0.05 to 1 :0.25, yet even more preferably from 1 :0.05 to 1 :0.20.

HYDROXYAPATITE COMPONENT

The term "apatite" denotes a family of mineral compounds, the chemical formula of which can be written in the following general form:

Meio(X0 ₄ )6Y ₂

In this formula, Me generally represents a divalent cation (Me ²⁺ ), X0 ₄ a trivalent anionic group (X0 ₄ ³ ) and Y a monovalent anion (Y ).

Calcium phosphate hydroxyapatite Caio (P0 ₄ ) ₆ (0H) ₂ crystallizes in the space group of the hexagonal system. This structure consists of a close-packed quasi-hexagonal stack of X0 ₄ groups, forming two types of parallel tunnels.

The existence of these tunnels gives apatites chemical properties akin to those of zeolites. Vacancies may also be created either by the departure of anions and cations, or by the presence of cations or anions of different valency. Apatites therefore appear to be particularly stable structures which may tolerate large gaps in their composition.

Hydroxyapatite should not be confused with tricalcium phosphate (TCP), which has a similar weight composition: Ca ₃ (P0 ₄ ) ₂ . The Ca/P molar ratio of TCP is 1.5 whereas it is 1.67 for hydroxyapatite. Industrial apatites sold as food additives or mineral fillers are, as a general rule, variable mixtures of TCP and hydroxyapatite.

Other salts of calcium and phosphate, including TCP, do not have the same properties as hydroxyapatite. Although TCP can also react with heavy metals, hydroxyapatite is more advantageous as it can enclose metals in the form of an insoluble, and therefore relatively inert, matrix.

Ca-DEFICIENT HYDROXYAPATITE

The hydroxyapatite in the composite may be deficient in calcium compared to a hydroxyapatite with a Ca/P molar ratio of 1.67. The Ca/P molar ratio of the calcium-deficient hydroxyapatite is preferably more than 1.5 and less than 1.67, more preferably with a Ca/P molar ratio more than 1.54 and less than 1.65.

The hydroxyapatite composite may comprise a calcium-deficient hydroxyapatite and has an overall Ca/P molar ratio higher than the calcium- deficient hydroxyapatite.

In some embodiments, the hydroxyapatite composite comprises:

- a calcium-deficient hydroxyapatite, preferably with a Ca/P molar ratio more than 1.5 and less than 1.67; and

- an activated carbon, wherein said activated carbon is present during the synthesis of such calcium-deficient hydroxyapatite.

Preferably the hydroxyapatite composite has a higher pore volume and/or a higher BET surface area compared to a calcium-deficient hydroxyapatite structure made using the same synthesis method but without the activated carbon.

The at least one activated carbon may be added to a vessel where the hydroxyapatite synthesis takes place, prior to or during the synthesis of the hydroxyapatite. That is to say, when the synthesis of the hydroxyapatite takes place in a vessel, the activated carbon may be added to the vessel before the synthesis is initiated or while the hydroxyapatite structure is synthetized in this vessel.

The activated carbon in the composite is preferably embedded or incorporated into or coated onto the hydroxyapatite structure or otherwise associated with the hydroxyapatite structure via cohesive forces.

Calcium may be and is preferably present in another form (other than the calcium-deficient hydroxyapatite) in the composite. Calcium carbonate may be present in the composite. The weight ratio of the calcium-deficient

hydroxyapatite to calcium carbonate is generally equal to or greater than 3, preferably equal to or greater than 4, more preferably equal to or greater than 5, yet more preferably greater than 7, most preferably equal to or greater than 9.

Generally, because of this other form of Ca in the composite, the hydroxyapatite composite generally has an overall Ca/P molar ratio higher than the calcium-deficient hydroxyapatite present in the hydroxyapatite composite. For that reason, in some embodiments, even though the calcium-deficient hydroxyapatite in the composite may have a Ca/P molar ratio less than 1.67, the entire composite may have a Ca/P molar ratio equal to or more than 1.67. In preferred embodiments, the calcium-deficient hydroxyapatite in the composite may have a Ca/P molar ratio of about 1.55-1.59, while the

hydroxyapatite composite may have a Ca/P molar ratio of about 1.60-1.67.

Other salts of calcium and phosphate, including TCP, do not have the same properties as hydroxyapatite or a hydroxyapatite-like structure. Although TCP can also react with metals, a hydroxyapatite of Ca/P=l.67 as well as a calcium- deficient hydroxyapatite (1.5 < Ca/P < 1.67) are more advantageous because they can enclose or entrap metals in an insoluble form, and therefore relatively inert, matrix.

METHOD OF MAKING THE COMPOSITE

Another aspect of the present invention relates to a process for producing a hydroxyapatite composite, which may include separate sources of calcium and phosphate or a source of calcium and phosphate and the addition of the additive during the hydroxyapatite synthesis from the separate sources of calcium and phosphate or from the source of calcium and phosphate.

When the process starts with separate sources of calcium and phosphate, the process generally comprises two steps: a reaction of the two sources to obtain a suspension (A) of calcium phosphate, and then an alkaline maturation to form a hydroxyapatite structure. This process is typically referred to as the“2-step” process.

When the process starts with a source of calcium and phosphate, the process generally comprises an alkaline maturation of the source of calcium and phosphate to form a hydroxyapatite structure. This process is typically referred to as the“l-step” process.

A preferred embodiment of the process for producing a hydroxyapatite composite according to the present invention comprises:

- in a first step, a source of calcium and a source of phosphate ions are mixed in water in a molar ratio that is adjusted to obtain a Ca/P molar ratio of between 0.5 and 1.6, preferably between 0.7 and 1.3, and reacting the source of calcium with the phosphate ions at a pH of between 2 and 8, in order to obtain a suspension (A) of calcium phosphate,

- in a second step, adding to the suspension (A) an alkaline compound

comprising hydroxide ions in order to set a pH of at least 7.5, preferably at least 8, or at least 8.5, or at least 9, or of at least 10; further adding an additional source of calcium in order to obtain a suspension (B) of composite having a Ca/P molar ratio of greater than 1.6, preferably greater than 1.65, and/or less than 1.75, to form a hydroxyapatite structure; and

- further adding at least one activated carbon in the first step, in the second step, or in both in the first and second steps.

When the activated carbon is added in the first step, it may be added at the beginning of the first step before the reaction takes place, during the reaction, or after the reaction is completed in the first step (this being preferred).

It is envisioned that the activated carbon may be added not all at once, for example in at least two portions, for example a first portion in the first step and another portion in the second step.

It is also envisioned that two or more activated carbons may be added. In an example, a first activated carbon is added in the first step and a second activated carbon is added in the second step. Alternatively, the first and second activated carbons may be added in the first step or in the second step.

A particular embodiment of the present invention relates to a process for producing the hydroxyapatite composite, comprising:

- in a first step, a source of calcium and a source of phosphate ions are mixed in water in a molar ratio that is adjusted to obtain a Ca/P molar ratio of between 0.5 and 1.6, preferably between 0.7 and 1.3, and reacting the source of calcium with the phosphate ions at a pH of between 2 and 8, in order to obtain a suspension (A) of calcium phosphate, and

- in a second step, adding to the suspension (A) an alkaline compound

comprising hydroxide ions in order to set a pH of at least 7.5, preferably at least 8, or at least 8.5, or at least 9, or of at least 10; further adding an additional source of calcium in order to obtain a suspension (B) of composite having a Ca/P molar ratio of greater than 1.6, preferably greater than 1.65, and/or less than 1.75, and further adding at least one activated carbon, to form a composite material comprising a hydroxyapatite structure.

An alternate embodiment of the present invention relates to a process for producing the hydroxyapatite composite, comprising:

- in a first step, a source of calcium and a source of phosphate ions are mixed in water in a molar ratio that is adjusted to obtain a Ca/P molar ratio of between 0.5 and 1.6, preferably between 0.7 and 1.3, and reacting the source of calcium with the phosphate ions at a pH of between 2 and 8, in order to obtain a suspension (A) of calcium phosphate, - further adding at least one activated carbon during the first step, such as at the beginning of the first step before the reaction takes place, during the reaction, or after the reaction is completed in the first step (this being preferred);

- in a second step, adding to the suspension (A) an alkaline compound

comprising hydroxide ions in order to set a pH of at least 7.5, preferably at least 8, or at least 8.5, or at least 9, or of at least 10; further adding an additional source of calcium in order to obtain a suspension (B) of composite having a Ca/P molar ratio of greater than 1.6, preferably greater than 1.65, and/or less than 1.75, to form a composite material comprising a hydroxyapatite structure.

An alternate process for producing the hydroxyapatite composite does not use an acid attack in the first step as explained above. This alternate process used an alkaline maturation of particles of a calcium phosphate compound. The calcium phosphate compound preferably has a Ca/P molar ratio of 1.5 or less, preferably between 0.50 and 1.35. This alternate process may comprise the following steps:

- forming an aqueous suspension comprising particles of a calcium phosphate compound having a Ca/P molar ratio of 1.5 or less, preferably between 0.50 and 1.35, more preferably particles containing brushite, yet more preferably particles containing >70 wt% brushite, most preferably particles containing >90 wt% brushite;

- adding an alkaline compound comprising calcium and hydroxide ions in order to increase the pH of the suspension to a value of at least 6.5, preferably at least 7, or at least 7.5, or at least 8, or of at most 11 in order to obtain a suspension (B’) having a Ca/P molar ratio of greater than 1.6, preferably greater than 1.65, and/or less than 1.75; and

- further adding at least one activated carbon to the suspension (B’) before, during or after the addition of the alkaline compound, preferably before or during the addition of the alkaline compound, to form the hydroxyapatite composite,

The calcium phosphate material may comprise monocalcium phosphate

(MCP) having the weight formula Ca(H ₂ P0 ₄ ) ₂ , dicalcium phosphate (DCP) having the weight formula CaHP0 ₄ , or the hydrate thereof, brushite having the weight formula CaHP0 ₄ .2H ₂ 0, and/or octacalcium having the weight formula Ca ₈ H ₂ (P0 ₄ ) ₆ .6.5H ₂ 0. The Ca/P molar ratios are respectively for these compounds: 0.5 (MCP), 1.0 (DCP and brushite), 1.33 (octacalcium). The calcium phosphate material may comprise particles containing brushite, preferably particles containing >70 wt% brushite, more preferably particles containing >90 wt% brushite.

In a preferred embodiment, the alternate process for producing the hydroxyapatite composite may comprise the following steps:

- forming an aqueous suspension comprising particles containing brushite, preferably particles containing >70 wt% brushite, more preferably particles containing >90 wt% brushite;

- adding an alkaline compound comprising calcium and hydroxide ions in order to increase the pH of the suspension to a value of at least 6.5, preferably at least 7, or at least 7.5, or at least 8, or of at most 11 in order to obtain a suspension

(B’) having a Ca/P molar ratio of greater than 1.6, preferably greater than 1.65, and/or less than 1.75; and

- further adding at least one activated carbon to the suspension (B’) before, during or after the addition of the alkaline compound, preferably before or during the addition of the alkaline compound, to form the hydroxyapatite composite,

wherein said suspension (B’) contains from 10 to 35 wt% solids, preferably from 15 to 25 wt% solids.

In this alternate process, the alkaline compound comprises calcium hydroxide.

The activated carbon is preferably incorporated or embedded into or coated onto the hydroxyapatite structure, or otherwise associated with the

hydroxyapatite structure via cohesive forces.

The activated carbon is in the form of a powder before it is added to at least one of the first and second steps of the 2-step method of making the composite or before it is added before or during the alkaline maturation step in the l-step method of making the composite.

In some embodiments, when the D50 particle size of the activated carbon is greater than 100 microns, the method of making the composite may further include grinding or milling the solid to achieve a D50 less than 100 microns or less than 90 microns, preferably less than 75 microns, or more preferably less than 63 microns, before the resulting powder is added to at least one of the first and second steps of the 2-step method of making the composite or before it is added before or during the alkaline maturation step in the l-step method of making the composite.

In some embodiments, when the activated carbon may be in the form of a powder (either sold‘as is’ or ground before use), the method of making the composite may further include sieving the powder of the activated carbon to remove large particles, such as those exceeding a size of 100 microns, or exceeding a size of 90 microns. For example, the powder of the activated carbon which passes through a sieve No. 170 (under ASTM El l) equivalent to a size of less than 90 microns, or through a sieve No. 200 (under ASTM El l) equivalent to a size of less than 75 microns, or through a sieve No. 230 (under ASTM El l) equivalent to a size of less than 63 microns can be added to at least one of the first and second steps of the 2-step method of making the composite or before it is added before or during the alkaline maturation step in the l-step method of making the composite.

In the present invention, the source of calcium in the 2-step method advantageously comprises calcium carbonate, or calcium oxide, or calcium hydroxide, or calcium chloride, or calcium nitrate, or calcium acetate. The source of calcium is more advantageously a limestone, or a mixture of limestone and calcium oxide or hydroxide. More advantageously, the source of calcium is in the form of powder or aqueous suspension of powder and the powder is selected from: calcium carbonate, calcium oxide, calcium hydroxide, or a mixture thereof, and the powder has a mean particle size of less than 300 pm.

It is advantageous in the 2-step method for the source of calcium selected from calcium carbonate, calcium oxide, calcium hydroxide or mixtures thereof to be in the form of a powder or aqueous suspension of powder, and to have a small particle size. In one recommended variant, the mean diameter of the particles of the powder is less than 300 pm, advantageously less than 200 pm and preferably less than 100 pm. The mean diameter in question is the D50, that is to say the diameter such that 50% by weight of the particles have a diameter less than said value.

In the present invention, various sources of phosphate ions in the 2-step method may be used, in particular:

- phosphoric acid,

- or a dihydrogen phosphate salt such as a sodium, potassium or ammonium dihydrogen phosphate salt, preferably a sodium dihydrogen phosphate salt,

- or a monohydrogen phosphate salt such as a sodium, potassium or ammonium monohydrogen phosphate salt, preferably a sodium monohydrogen phosphate salt. In the present invention, phosphoric acid in the 2-step method is preferred due to its greater availability and lower cost compared to dihydrogen and monohydrogen phosphate salts.

In the process according to the invention, in the first step of the 2-step method the Ca/P molar ratio is in particular between 0.50 and 1.6, preferably between 0.50 and 1.35, more preferably between 0.70 and 1.30, yet more preferably between 0.80 and 1.20.

During the first step of the 2-step method where calcium and phosphate are used in a Ca/P molar ratio of between 0.5 and 1.6 and where they are reacted at a pH between 2 and 8, the compounds formed in the suspension (A) are a mixture of monocalcium phosphate (MCP) having the weight formula Ca(H ₂ P0 ₄ ) ₂ , of dicalcium phosphate (DCP) having the weight formula CaHP0 ₄ , or the hydrate thereof, brushite, having the weight formula CaHP0 ₄ .2H ₂ 0, and of octacalcium having the weight formula Ca ₈ H ₂ (P0 ₄ ) ₆ .6.5H ₂ 0. The Ca/P molar ratios are respectively for these compounds: 0.5 (MCP), 1.0 (DCP and brushite), 1.33 (octacalcium).

In order to promote, in the first step of the 2-step method, the formation of MCP and DCP, a Ca/P ratio of between 0.50 and 1.35, preferably between 0.7 and 1.30, is favored. This Ca/P molar ratio is particularly advantageous when the source of calcium from the first step comprises calcium carbonate, and the source of phosphate is phosphoric acid (H ₃ P0 ₄ ) or is a dihydrogen phosphate salt such as a sodium or potassium or ammonium salt. Specifically, this makes it possible to obtain a rapid attack of the calcium carbonate and a rapid degassing of the C0 ₂ . In addition to calcium carbonate, the source of calcium may comprise calcium oxide, or calcium hydroxide, or calcium chloride, or calcium nitrate, or calcium acetate.

In other embodiments, in order to promote, in the first step of the 2-step method, the formation of DCP and octacalcium, a Ca/P ratio of between 1.4 and 1.6, preferably between 1.4 and 1.5, is favored. This molar ratio is advantageous when use is made of a source of calcium having less than 30% by weight of carbonate, such as preferably: calcium oxide, or calcium hydroxide, or calcium chloride, or calcium nitrate, or calcium acetate.

In the present invention, in the first step of the 2-step method, the source of calcium and the phosphate ions are in general reacted for at least 0.1 hour, preferably at least 0.5 hour. It is not useful to react the source of calcium and the phosphate ions over excessively long durations. Advantageously, the source of calcium and the phosphate ions in the first step of the 2-step method are reacted for at most 4 hours, more advantageously at most 2 hours, or even at most 1 hour. For example, a duration of 1 hour at pH 5 already enables a good reaction of the calcium and the phosphate ions, and makes it possible to sufficiently release the C0 ₂ when a source of calcium comprising calcium carbonate is used, before moving on to the (second) alkaline maturation step.

In the present invention, in the (second) alkaline maturation step, the suspension (B) or (B’) of the composite in general has a Ca/P molar ratio of at most 5, preferably of at most 3, more preferably still of at most 2, yet more preferably of at most 1.75, most preferably of at most 1.7.

In the present invention, it is advantageous, in the second step, for the alkaline compound used, that comprises hydroxide ions, to be sodium hydroxide and/or calcium hydroxide.

In the present invention, it is advantageous, in the alkaline maturation step of the l-step method, for the alkaline compound used that comprises calcium and hydroxide ions, to include or consist of calcium hydroxide.

In the process according to the invention, it is particularly advantageous in the 2-step method for the additional source of calcium to be selected from calcium chloride, calcium nitrate, or calcium acetate, preferably calcium chloride, and for it to be added in addition to the alkaline compound, in order to finely adjust the Ca/P ratio and in order to limit the concentration of phosphorus element in the aqueous solution (C) of the suspension (B) to at most 5 mmol, advantageously to at most 0.5 mmol, more advantageously to at most 0.05 mmol of phosphorus element per litre of aqueous solution (C). Specifically, this makes it possible, coupled with the use of hydroxide ions for setting the pH of the second step, to limit the losses of phosphates in the process waters.

In the present invention, in general, the stirring and the density of suspension (B) or (B’), in the (second) alkaline maturation step and

advantageously also of the suspension (A) in the first step, are adjusted in order to avoid the appearance of a calcium phosphate gel having a viscosity of at least 200 cps. The viscosity of the composite suspension (B) or (B’) in the (second) alkaline maturation step in the method of making of the present invention is typically about 10 cps (mPa.s). Specifically, the production of a gel, even in the presence of the (second) alkaline maturation step, results in solid particles of small particle size being produced, with weight-average D50 values of less than 10 mih, which is a disadvantage for certain applications of liquid effluents such as those that use a sludge blanket.

The suspended solids density of the suspension (A) in the first step is in general at most 25% by weight.

The suspended solids density of the suspension (B) or (B’) in the (second) alkaline maturation step is in general at most 35%, preferably at most 25% by weight. The suspended solids density of the suspension (A) and or of the suspension (B) or (B’) is advantageously at least 5 wt%, more advantageously at least 10 wt%, most advantageously at least 15 wt%. A preferred range of suspended solids density of the suspension (B) or (B’) in the (second) alkaline maturation step is from 15 wt% to 25 wt%. It has been indeed observed that a too low density of suspension decreases the efficacy of the produced reactant particles in heavy metal adsorption. Moreover a too low density of suspension induces longer time of water separation when decantation or filtration is used in the process.

In the process of the present invention, the stirring of the suspension during the first and (second) alkaline maturation steps corresponds generally to a stirring dissipated energy in the reactors volume of at least 0.2 and at most 1.5 kW/ m ³ , preferably at least 0.5 and at most 1.0 kW/ m ³ .

In a first embodiment of the present invention, the first step in the 2-step process is carried out at a temperature of less than 50°C, preferably at a temperature of at most 45°C, or at a temperature of at most 40°C, more preferably at a temperature of at most 35°C. This makes it possible to obtain a composite at the end of the (second) alkaline maturation step in the form of particles of large to medium particle size and having a high specific surface area.

An embodiment of the present invention further relates to a particle of hydroxyapatite composite,

- having a mean size of at least 20 pm, or at least 25 pm, or at least 30 pm;

- having a specific surface area of at least 120 m ² /g, or at least 130 m ² /g, at least 140 m ² /g; and/or

- having a total pore volume of at least 0.3 cm ³ /g, at least 0.32 cm ³ /g. or at least 0.4 cm ³ /g.

In a second embodiment (less preferred) of the present invention, the first step in the 2-step process is carried out at a temperature of at least 50°C, preferably of at least 55°C, or of at least 60°C. This makes it possible to obtain a composite in the second step in the form of particles of small particle size and having a lower specific surface area. The invention relates in particular to a particle of composite obtained by the process according to this second embodiment, having a mean size of at most 30 pm, preferably of at most 20 pm, and having a specific surface area of at least 15 m ² /g, preferably of at least 50 m ² /g.

In the first or second embodiment of the process of the present invention, it is advantageous for the (second) alkaline maturation step to be carried out at a temperature of at least 45°C, preferably of at least 50°C, more preferably of at least 55°C, or of at least 60°C, or of at least 80°C, and/or of at most 90°C.

Specifically, this makes it possible to rapidly convert the calcium phosphate compound of low Ca/P ratio (such as brushite) into the composite comprising a hydroxyapatite of higher Ca/P ratio, with a good fixation of the hydroxide ions at the core and at the surface of the composite, and to more rapidly consume the phosphates from the solution of the suspension (B) or (B’). Advantageously, the (second) alkaline maturation step is carried out for a duration of at least 0.5 hour.

In general, the addition of the alkaline compound comprising hydroxide ions in order to set the pH of the (second) alkaline maturation step, and of the additional source of calcium in order to obtain a suspension (B) of composite having a Ca/P molar ratio of greater than 1.6 last no more than 6 hours, advantageously no more than 4 hours, or no more than 2.5 hours; at higher temperature such as at 50 or at 60°C a duration of generally one to 2 hours is sufficient, as at 40°C the duration for alkaline compound addition to set the pH of the (second) alkaline maturation step is generally longer: and about 2 to 2.5 hours are needed. Preferably, the alkaline compound addition is stopped when the pH remains at the set value for at least 15 minutes.

It is to be understood that the time for reaction in the (second) alkaline maturation step is generally dependent of the end pH of the (second) alkaline maturation step, and it may be impacted by the size of the equipment that is used to make the composite. It was observed for example that, when using the same temperature for the (second) alkaline maturation step, for a 3-L or 5-L reactor, the reaction time needed to reach the pH of about 8 to 9 in the (second) alkaline maturation step was generally from 1 hour to 3 hours, whereas in a 200-L reactor, the reaction time needed to reach the pH of about 8 to 9 in the second step was generally from 2 hours to 6 hours

The addition of hydroxide ions for setting the pH of the (second) alkaline maturation step, and the addition of the additional source of calcium can be carried out by using calcium hydroxide to provide both hydroxide ions and additional source of calcium.

Advantageously, the addition of the activated carbon may be carried out once the addition of hydroxide ions for setting the pH of the (second) alkaline maturation step and the addition of the additional source of calcium are completed.

Alternatively, the addition of the additive or a precursor thereof may be carried out before or during the addition of hydroxide ions for setting the pH of the (second) alkaline maturation step.

In a particular preferred embodiment, the method takes place in two steps, a first step called "acid attack" and a second step, called "lime maturation". The first step includes the decarbonation of calcium carbonate (as source of calcium) by the addition of phosphoric acid (as source of phosphate ions). Carbonic acid formed by this acid attack decomposes into water and carbon dioxide, as soon as the maximum solubility of C0 ₂ in the aqueous phase is reached. Calcium hydrogenphosphate (CaHP0 ₄ .2H ₂ 0, also known as brushite) formed in the first step has a Ca/P molar ratio of 1. However, the Ca/P molar ratio of a

stoichiometric hydroxyapatite is 1.67. So there is a calcium deficit that has to be filled by the second step. In the second step "lime maturation", the addition of lime (Ca(OH) ₂ ) as an additional source of calcium to the brushite contributes the calcium necessary to approach a stoichiometric hydroxyapatite. But this addition of lime also allows the addition of hydroxide anions necessary for the structure of the hydroxyapatite and the neutralization of H ⁺ hydrogenphosphate. This method has the advantage that it allows the synthesis of hydroxyapatite from relatively inexpensive reagents, compared to other methods, and uses relatively mild conditions of synthesis (temperature and pH).

In some embodiment, the synthetized hydroxyapatite in the composite approaches the molar Ca/P hydroxyapatite stoichiometry of 1.67 but generally comprises a Ca/P more than 1.5 and less than 1.67, that is to say, the synthetized hydroxyapatite in the composite is deficient in calcium compared to the stoichiometry. Some of the calcium source (e.g., calcium carbonate when it is used in the first step) which is not utilized in the hydroxyapatite would remain inside the hydroxyapatite composite composition.

In this particular preferred method, the first step is to attack limestone with phosphoric acid at a temperature of from 20 to 25°C to make a brushite type structure. At the end of the addition of acid, the second step is initiated by heating the mixture up to at least 50°C. A suspension of Ca(OH) ₂ (such as 25 wt%) is then added to maintain the pH of the suspension at a maximum 8.9. The second step preferably uses an overall Ca/P molar ratio of about 1.67. The goal of this second step is to convert the brushite type structure created in the first step to a hydroxyapatite structure in the second step.

During the synthesis of apatite structure and more precisely during the second step corresponding to the addition of the hydroxide ions, the pH reaches 8-8.5 to a maximum of 8.9, and this addition becomes more difficult, if not impossible without raising the pH too much. This moment is called "plateau".

The plateau is where the activated carbon is preferably added out at one time, although the addition of activated carbon may be carried out in several increments. However, it is to be understood that the addition of the activated carbon in the (second) alkaline maturation step may be carried out during the same period of time when the hydroxide ions are added (that is to say, before the pH plateau is reached), such as a one-time addition, in several increments, or in a continuous manner.

The activated carbon needs to be present during the hydroxyapatite synthesis but its addition does not have to necessarily take place at the time of the hydroxyapatite synthesis. The activated carbon may be added prior to the plateau in the (second) alkaline maturation step, or even before the conversion of the low Ca/P calcium-phosphate compound (such as brushite of Ca/P = 1), either used as a source of calcium and phosphate or formed in the first step, to the hydroxyapatite structure formed in the (second) alkaline maturation step. For example, the activated carbon may be added before the addition of the hydroxide ions is initiated in the (second) alkaline maturation step. The activated carbon may be added even during the first step, particularly if the activated carbon is compatible with the pH condition of the first step, which is generally less than 7, or less than 6.5, or even less than 6.“Compatible” here means that the activated carbon added in the first step is not degraded/reacted or otherwise rendered ineffective as an activated carbon for making a hydroxyapatite composite in the (second) alkaline maturation step.

The suspension (B) or (B’) may be left to cool for 1 to 24 hours, preferably at least 10 hours, down to ambient temperature (generally 20-25 °C). This makes it possible to mature the composite and to reduce the residues of MCP/DCP or brushite, or of octacalcium (e.g., precipitated during the first step), into hydroxyapatite and into calcium phosphate and calcium hydroxide complexes, within the suspension (B).

In preferred embodiments, the process of making the hydroxyapatite composite does not comprise an in-situ polymerization of at least one polymer during the synthesis of the hydroxyapatite composite. It is preferred that the hydroxyapatite composite does not contain an organic polymer crosslinked network, for example created by polyvinyl alcohol.

When an optional additive is used in the making of the hydroxyapatite composite, the optional additive or a precursor thereof may be added at the same time as the activated carbon. Or the activated carbon and the optional additive may be added at different times during the hydroxyapatite synthesis. Preferably the activated carbon and the optional additive are added at the beginning or during the (second) alkaline maturation step.

Optionally, in the process of making the composite according to the present invention, at the end of the (second) alkaline maturation step, the suspension (B) or (B’) comprises an aqueous solution (C) and composite particles, and

- in a third step, a portion of the aqueous solution (C) is separated from the suspension (B) or (B’) in order to obtain an aqueous suspension (D) comprising at least 18% and at most 50% of composite particles, or in order to obtain a wet solid (D') comprising at least 50% and at most 80% of composite particles, or a pulverulent solid (D") comprising at least 80% and at most 95% of composite particles and at least 5% and at most 20% of water.

In a third step, the separation may comprise a dewatering step which increases the solids content. The separation may comprise for example a filter, such as a filter press. This type of separation may provide an aqueous suspension (D) or a wet solid (D') of higher solids content than the suspension (B) or (B’) taken out of the reactor.

In some embodiments, the method for making the hydroxyapatite composite particles may further comprise drying the suspension (B) or aqueous suspension (D) or wet solid (D') at a temperature between 50 to l80°C, preferably from 80 to 130 °C, or more preferably from 90 to 120 °C, most preferably from 95 to 115 °C.

Drying may comprise any suitable technique suitable for decreasing the water content of the suspension (B) or (B’) or aqueous suspension (D) or wet solid (D'), such as, but not limited to, spray drying, flash drying, and/or drying in a fluidized bed.

In some embodiments, the method for making the hydroxyapatite composite particles may comprise spray drying the suspension (B) or (B’) or aqueous suspension (D) to provide a pulverulent solid (D").

Consequently, the present invention also relates to an aqueous suspension (D) comprising at least 25%, preferably at least 40% and at most 50% of composite particles obtained by the present method, or to a wet solid (D') comprising at least 50% and at most 80% of composite particles obtained by the present method, or a pulverulent solid (D") comprising at least 70%, preferably at least 80%, and at most 95% of composite particles obtained by the present process and at least 5% and at most 20% of water.

The composite obtained according to the present invention is effective for treating substances contaminated by metallic and/or non-metallic elements, for example in the form of cations and/or oxyanions, in particular contaminated by Hg or its cation, As, Se, and/or B or their respective oxyanions.

ADSORBENT

Consequently another embodiment of the present invention relates to an adsorbent material for removal of contaminants from a water or gas effluent, comprising :

- one hydroxyapatite composite comprising at least one activated carbon;

- two or more hydroxyapatite composites, wherein the one activated carbons in the hydroxyapatite composites are different; or

- a blend of a hydroxyapatite without activated carbon and at least one hydroxyapatite composite comprising at least one activated carbon.

USE OF HYDROXYAPATITE COMPOSITE OR SORBENT

The present invention also relates to the use of the hydroxyapatite composite or the adsorbent material comprising at least one hydroxyapatite composite for removing at least a portion of one or more contaminants, for example organics (e.g., PAHs, phenolic compounds, naphtol and derivatives) and/or metals, non-metals, in the form of their cations and/or oxyanions, particularly metallic contaminants such as Hg or its cation, and non-metallic contaminants such as As, B, and/or Se, or their respective oxyanions, from a substance, such as water or gas effluent.

The present invention also relates to a method for treating a substance to be treated such as water or gas effluent or for removing at least a portion of one or more contaminants from a substance to be treated, for example organic contaminants (e.g., PAHs, phenolic compounds, naphtol and derivatives) or inorganic contaminants in the form of metals, non-metals, their cations and/or oxyanions, particularly Hg or its cation, As, B, and/or Se, or their respective oxyanions, comprising contacting the hydroxyapatite composite or the adsorbent material comprising at least one hydroxyapatite composite with the substance to be treated.

The present invention also relates to a method for removing at least a portion of Hg (in the form of cation) from a water or gas effluent, in which the hydroxyapatite composite comprising at least one activated carbon or the adsorbent material comprising at least one hydroxyapatite composite contacts the water or gas effluent to remove at least a portion of Hg. The present invention also relates to a method for removing at least a portion of selenium oxyanions from a water effluent, in which the hydroxyapatite composite or the adsorbent material comprising at least one hydroxyapatite composite contacts the water effluent to remove at least a portion of selenium oxyanions. In preferred embodiments the composite comprises activated carbon, and optionally S°, iron in the form of Fe°, and optionally S°, iron(III) hydroxide and/or iron(III) oxyhydroxide, or combination thereof.

The present invention also relates to a method for removing at least a portion of borate ions from a water effluent, in which the hydroxyapatite composite or the adsorbent material comprising at least one hydroxyapatite composite contacts the water effluent to remove at least a portion of borate. In preferred embodiments, the composite comprises at least one activated carbon.

The present invention also relates to a method for removing at least a portion of As oxyanions from a water effluent, in which the hydroxyapatite composite or the adsorbent material comprising at least one hydroxyapatite composite contacts the water effluent to remove at least a portion of As oxyanions.

The present invention also relates to a process for purifying a substance contaminated by metallic and/or non-metallic contaminants, for example in the form of metals, non-metals, their cations and/or oxyanions, according to which the substance is brought into contact with the hydroxyapatite composite of the present invention, whether it be in the form of the suspension (D) or the wet solid (D') or the pulverulent solid (D"), in order that at least a portion of the contaminants is adsorbed by the composite. In the purification or removal process according to the invention, the contaminated substance or effluent may be a flue gas containing metallic and/or non-metallic contaminants such as Al, Ag, As, Ba, Be, Bi, Ce, Co, Cd, Cu, Cr,

Fe, Hf, Hg, La, Li, Mg, Mn, Mo, Ni, Pb, Pd, Rb, Sb, Se, Sn, Sr, Th, Ti, U, V, Y, Zn, and/or Zr, preferably Cd, Pb, Zn, Hg, Se, and/or As and according to which the hydroxyapatite composite or an adsorbent comprising at least one

hydroxyapatite composite, whether it be in the form of the aqueous suspension (D) or the wet solid (D') or the pulverulent solid (D"), is dispersed in the flue gases, the flue gases being at a temperature of at least l00°C, or of at least l20°C, or of at least l50°C, and preferably not more than 1 l00°C, or of at most

300°C, of at most 250°C, or of at most 200°C, the resulting mixture then being subjected to a separation in order to obtain a resulting solid and a flue gas partially purified of metallic and/or non-metallic elements.

In the purification or removal process according to the invention, the contaminated substance or effluent may be a liquid effluent containing metallic contaminants, such as: Al, Ag, Ba, Be, Ce, Co, Cd, Cu, Cr, Fe, Hg, La, Li, Mo, Ni, Pb, Pd, Rb, Sb, Sn, Th, Ti, U, V, Y, Zn and/or non-metallic elements such as As, B, F, Se, whether these elements may be in the form of cations and/or anions, such as oxyanions, according to which the hydroxyapatite composite or an adsorbent material comprising the hydroxyapatite composite (preferably in suspension form) is mixed into the liquid effluent for a sufficient time so that the hydroxyapatite composite adsorbs at least a portion of the metallic and/or non- metallic contaminants and the mixture is subjected to a clarification in order to produce a liquid partially purified of metallic and/or non-metallic contaminants, on the one hand, and the composite loaded with metallic and/or non-metallic elements that is removed from the mixture. Preferably, the composite is used with the liquid effluent in a contact reactor, such as a sludge blanket reactor or a fluidized bed. The contact time between the composite and the liquid effluent is in general at least one minute, advantageously at least 15 minutes, more advantageously at least 30 minutes, even more advantageously at least one hour. In one particularly advantageous embodiment of the invention, the liquid effluent is introduced into a sludge blanket contact reactor in which the composite is present at a weight concentration of at least 0.5% by weight and in general at most 10% by weight; a liquid is recovered as overflow from the sludge blanket reactor; a flocculant is added to the recovered liquid in order to form a mixture comprising particles of the hydroxyapatite composite entrained out of the contact reactor and flocculated; said mixture is then introduced into a settling tank where the mixture is separated into:

- the liquid partially purified of metallic elements and/or of non-metallic elements, and said liquid is recovered as overflow from the settling tank, - and into an underflow from the settling tank comprising flocculated and settled particles of composite recovered as underflow from the settling tank;

and at least one portion of the underflow from the settling tank containing flocculated and settled particles of composite is recycled to the sludge blanket contact reactor. The effectiveness of the treatment of metallic elements and/or non-metallic elements may be monitored by comparing the concentrations of the elements upstream (in the liquid effluent) and downstream of the treatment (in the partially treated liquid), for example by an automatic analyser or by sampling and analysis. The composite charge of the contact reactor is in general regularly renewed in portions. For example, by partial purging of the composite loaded with metallic and/or non-metallic elements at the underflow from the settling tank, and by adding fresh composite to the contact reactor. Such a process thus ensures a "chemical polishing" of the liquid effluents. The process is particularly advantageous in the case where the liquid partially purified of metallic elements and/or non-metallic elements is then treated in a biological treatment plant producing sewage sludges. This makes it possible to reduce the concentrations of such elements of said sewage sludges and to reutilize them, for example in agriculture or in land development.

In the purification process according to the invention, the contaminated substance may be a solid residue or a soil contaminated by metallic elements such as Al, Ag, Ba, Be, Ce, Co, Cd, Cu, Cr, Fe, Hg, La, Li, Mo, Ni, Pb, Pd, Rb, Sb, Sn, Th, Ti, U, V, Y, Zn and/or non-metallic elements such as As, B, F, Se, according to which the composite or the adsorbent material comprising the composite (for example in the form of the aqueous suspension (D) or the wet solid (D') or the pulverulent solid (D") of the composite) is injected into the solid residue or the soil in the vicinity of the metallic and/or non-metallic elements for a sufficient contact time so that the composite adsorbs at least a portion of the metallic and/or non-metallic elements.

In preferred embodiments of the use or method for purifying or removing contaminants, the composite may further comprise an optional additive such as sulfur, chitosan, hopcalite, at least one iron in the form of Fe°, iron(III) hydroxide and/or iron(III) oxyhydroxide, or combination thereof; preferably may further comprise an optional additive such as sulfur, iron in the form of Fe°, iron(III) hydroxide and/or iron(III) oxyhydroxide, or combination thereof; more preferably may further comprise sulfur (S°), Fe°, iron(III) hydroxide, and/or iron(III) oxyhydroxide (FeOOH) as optional additive.

In particular the present invention relates to the following embodiments:

ITEM 1. A hydroxyapatite composite which comprises:

a hydroxyapatite; and

at least one activated carbon which is present during synthesis of the hydroxyapatite.

ITEM 2. The hydroxyapatite composite according to ITEM 1, wherein at least one activated carbon increases the porosity of the hydroxyapatite, preferably so that the hydroxyapatite composite has a higher total pore volume and/or has a higher BET surface area than a hydroxyapatite material made without the activated carbon.

ITEM 3. The hydroxyapatite composite according to any of the preceding ITEMS, wherein the at least one activated carbon which is present during synthesis of the hydroxyapatite is added before the synthesis of the

hydroxyapatite is initiated or during the synthesis of the hydroxyapatite.

ITEM 4. The hydroxyapatite composite according to any of the preceding ITEMS, comprising a weight ratio of hydroxyapatite to activated carbon (HAP:AC) of from 1 :0.0l to 1 :0.5, preferably from 1 :0.02 to 1 :0.4 or from 1 :0.03 to 1 :0.4, more preferably from 1 :0.04 to 1 :0.3, yet more preferably from 1 :0.05 to 1 :0.25, yet even more preferably from 1 :0.05 to 1 :0.20; or

comprising at least 2 wt%, or at least 4 wt%, of the activated carbon based on the total weight of dry matter and/or at most 50 wt%, or at most 40 wt%, or at most 30 wt%, or at most 20 wt% of the activated carbon based on the total weight of dry matter.

ITEM 5. The hydroxyapatite composite according to any of the preceding ITEMS, comprising at least 50wt% hydroxyapatite, advantageously at least 60wt% and more advantageously still at least 70wt% hydroxyapatite or at least

75wt% hydroxyapatite based on the total weight of dry matter.

ITEM 6. The hydroxyapatite composite according to any of the preceding ITEMS, comprising, based on the total weight of dry matter:

- water, of the order of from 1 wt% to 20 wt%, advantageously from 2 wt% to 20 wt%. ITEM 7. The hydroxyapatite composite according to any of the preceding ITEMS, comprising, based on the total weight of dry matter:

- calcium carbonate in an amount of less than 20 wt% and more than 0 wt%, preferably from 1 wt% to 19 wt%, more preferably from 2 wt% to 18 wt%, based on the total weight of dry matter.

ITEM 8. The hydroxyapatite composite according to any of the preceding ITEMS, comprising, based on the total weight of dry matter:

- less than 1 wt% of calcium dihydroxide Ca(OH) ₂ , preferably less than 0.5 wt% calcium dihydroxide, more preferably less than 0.3 wt% calcium dihydroxide, even more preferably less than 0.2 wt% calcium dihydroxide, or even less than 0.1 wt% Ca(OH) ₂ ).

ITEM 9. The hydroxyapatite composite according to any of the preceding ITEMS, wherein the hydroxyapatite is a calcium- deficient hydroxyapatite, preferably with a Ca/P molar ratio more than 1.5 and less than 1.67, more preferably with a Ca/P molar ratio more than 1.54 and less than 1.65.

ITEM 10. The hydroxyapatite composite according to any of the preceding ITEMS, wherein the at least one activated carbon in the composite is embedded or incorporated into the hydroxyapatite or coated onto the hydroxyapatite.

ITEM 11. The hydroxyapatite composite according to any of the preceding ITEMS, wherein the hydroxyapatite composite excludes a polymer, such as excludes chitosan and/or polyvinyl alcohol.

ITEM 12. The hydroxyapatite composite according to any of the preceding ITEMS, being inorganic.

ITEM 13. The hydroxyapatite composite according to any of the ITEMS 1 to 11, further comprising an optional additive which is present during the

hydroxyapatite synthesis.

ITEM 14. The hydroxyapatite composite according to ITEM 13, wherein the at least one optional additive comprises chitosan; hopcalite; clays (e.g., bentonite); zeolites; sulfur; a metal in the form of metal of oxidation state 0, salt, oxide, oxyhydroxide, or hydroxide being selected from the group consisting of aluminium, tin, a transition metal selected from Groups 3-12 of the June 2016 IUPAC Periodic Table of Elements, and mixtures thereof; or combinations of two or more thereof; the metal in the form of metal of oxidation state 0, salt, oxide, oxyhydroxide, or hydroxide being preferably selected from the group consisting of aluminium, tin, iron, titanium, nickel, copper, zinc, zirconium, lanthanum, cerium, and mixtures thereof; the metal in the form of metal of oxidation state 0, salt, oxide, oxyhydroxide, or hydroxide being more preferably selected from the group consisting of aluminium, tin, iron, nickel, copper, zinc, lanthanum, cerium, and mixtures thereof; or

wherein the at least one optional additive comprises chitosan, hopcalite, iron in the form of metal, salt, oxide, oxyhydroxide, or hydroxide, or combinations of two or more thereof; or

wherein the at least one optional additive comprises hopcalite, iron in the form of metal, salt, oxide, oxyhydroxide, or hydroxide, preferably in the form oxyhydroxide, or hydroxide, or combinations of two or more thereof

ITEM 15. The hydroxyapatite composite according to any of the ITEM 13 or 14, wherein the at least one optional additive comprises iron in the form of metal, salt, oxide or hydroxide, or combinations of two or more thereof, preferably wherein the iron in the additive is in the oxidation state 0, 2 or 3.

ITEM 16. The hydroxyapatite composite according to any of the ITEMS 1-15, wherein the additive comprises an activated carbon or blend of two or more activated carbons, wherein said activated carbon or blend of two or more activated carbons is selected when a 0.3 wt% dispersion in deionized water provides a pH of 5 or more.

ITEM 17. The hydroxyapatite composite according to any of the preceding ITEMS, being in the form of particles, and further having at least one of the following:

- having a mean size of at least 20 pm, or at least 25 pm, or at least 30 pm;

and/or

- having a specific surface area of at least 120 m ² /g, or at least 130 m ² /g, or at least 140 m ² /g; and/or

- having a total pore volume of at least 0.3 cm ³ /g, or at least 0.32 cm ³ /g, or at least 0.4 cm ³ /g.

ITEM 18. The hydroxyapatite composite according to any of the preceding ITEMS, being in the form of particles

- having a mean particle size of at least 20 pm and at most 60 pm, preferably at least 25 pm and at most 60 pm, more preferably at least 30 pm and at most 60 pm.

ITEM 19. The hydroxyapatite composite according to any of the preceding ITEMS, wherein the hydroxyapatite composite does not contain an organic polymer crosslinked network, for example created by in-situ polymerization of at least one polymer during the synthesis of the hydroxyapatite composite. ITEM 20. The hydroxyapatite composite according to any of the preceding ITEMS, wherein the activated carbon in the composite is in a powder form with an average particle size of at most 500 microns, preferably at most 400 microns, or at most 300 microns, or at most 200 microns, or at most 100 microns, or at most 80 microns, or at most 60 microns, and/or at least 5 microns, or at least 10 microns.

ITEM 20’. The hydroxyapatite composite according to any of the ITEMS 1-20, further comprising sulfur (S°), preferably comprising at least 2 wt%, or at least 4 wt%, of sulfur (S°) based on the total weight of dry matter and/or or at most 40 wt%, or at most 30 wt%, or at most 20 wt% of sulfur (S°) based on the total weight of dry matter.

ITEM 21. Process for producing a hydroxyapatite composite of any of the ITEMS 1-20 & 20’, according to which:

- in a first step, a source of calcium and a source of phosphate ions are mixed in water in a molar ratio that is adjusted to obtain a Ca/P molar ratio of between

0.5 and 1.6, preferably between 0.7 and 1.3, and reacting the source of calcium with the phosphate ions at a pH of between 2 and 8, in order to obtain a suspension (A) of calcium phosphate,

- in a second step, adding to the suspension (A) an alkaline compound

comprising hydroxide ions in order to set a pH of at least 7.5, preferably at least 8, or at least 8.5, or at least 9, or of at least 10; further adding an additional source of calcium in order to obtain a suspension (B) of composite having a Ca/P molar ratio of greater than 1.6, preferably greater than 1.65, and/or less than 1.75, to form a hydroxyapatite structure; and

- further adding at least one activated carbon in the first step, in the second step, or in both in the first and second steps preferably in the second step.

ITEM 22. Process for producing a hydroxyapatite composite of any of the ITEMS 1-20 & 20’, according to which:

- in a first step, mixing a source of calcium and a source of phosphate ions in water, in a molar ratio adjusted to obtain a Ca/P molar ratio of between 0.5 and 1.6, and reacting the source of calcium with the phosphate ions at a pH of between 2 and 8, to obtain a suspension (A) of calcium phosphate, and

- in a second step, adding to the suspension (A) an alkaline compound comprising hydroxide ions to set a pH of at least 7.5, preferably at least 8, or at least 8.5, or at least 9, adding an additional source of calcium and adding the activated carbon order to obtain a suspension (B) of the hydroxyapatite composite.

ITEM 23. Process for producing a hydroxyapatite composite of any of the ITEMS 1-20 & 20’, according to which:

- in a first step, a source of calcium and a source of phosphate ions are mixed in water in a molar ratio that is adjusted to obtain a Ca/P molar ratio of between 0.5 and 1.6, preferably between 0.7 and 1.3, and reacting the source of calcium with the phosphate ions at a pH of between 2 and 8, in order to obtain a suspension (A) of calcium phosphate,

- further adding at least one activated carbon in the first step, such as at the beginning of the first step before the reaction takes place, during the reaction, or after the reaction is completed in the first step (this being preferred);

- in a second step, adding to the suspension (A) an alkaline compound comprising hydroxide ions in order to set a pH of at least 7.5, preferably at least 8, or at least 8.5, or at least 9, or of at least 10; further adding an additional source of calcium in order to obtain a suspension (B) of composite having a Ca/P molar ratio of greater than 1.6, preferably greater than 1.65, and/or less than 1.75, to form a composite material comprising a hydroxyapatite structure ITEM 24. Process for producing a hydroxyapatite composite of ITEM 21, according to which:

when the activated carbon is added in the first step, it is added at the beginning of the first step before the reaction between the source of calcium and the phosphate ions takes place, during the reaction, or after the reaction is completed in the first step (this being preferred).

ITEM 25. Process according to any of the ITEMS 21 to 24, wherein the source of calcium comprises calcium carbonate.

ITEM 26. Process according to any of the ITEMS 21 to 25, wherein the source of phosphate ions comprises phosphoric acid,

ITEM 27. Process according to any of the ITEMS 21 to 26, wherein in the second step, the alkaline compound used that comprises hydroxide ions is sodium hydroxide and/or calcium hydroxide.

ITEM 28. Process according to any of the ITEMS 21 to 27, wherein the stirring and the density of suspension, in the second step and advantageously also in the first step, are adjusted in order to avoid the appearance of a calcium phosphate gel having a viscosity of at least 200 cps. ITEM 29. Process according to any of ITEMS 21-28 wherein the first step is carried out at a temperature of less than 40°C, preferably less than 35°C and wherein the second step is carried out at a temperature of at least 40°C, preferably of at least 45°C, more preferably of at least 50°C.

ITEM 30. Process according to any of ITEMS 21-29 characterized in that it does not comprise an in-situ polymerization of at least one polymer during the synthesis of the hydroxyapatite composite,

ITEM 31. Process according to any of ITEMS 21-30 characterized in that the hydroxyapatite composite does not contain an organic polymer crosslinked network, for example created by polyvinyl alcohol.

ITEM 32. Process for producing the hydroxyapatite composite of any of ITEMS 1-20 & 20’, comprising the following steps:

- forming an aqueous suspension comprising particles of a calcium phosphate compound having a Ca/P molar ratio of 1.5 or less, preferably between 0.50 and 1.35, more preferably particles containing brushite, yet more preferably particles containing >70 wt% brushite, most preferably particles containing >90 wt% brushite;

- adding an alkaline compound comprising calcium and hydroxide ions in order to increase the pH of the suspension to a value of at least 6.5, preferably at least 7, or at least 7.5, or at least 8, or of at most 11 in order to obtain a suspension

(B’) having a Ca/P molar ratio of greater than 1.6, preferably greater than 1.65, and/or less than 1.75; and

- further adding at least one activated carbon to the suspension (B’) before, during or after the addition of the alkaline compound, to form the

hydroxyapatite composite,

wherein said suspension (B’) contains from 10 to 35 wt% solids, preferably from 15 to 25 wt% solids.

ITEM 33. Process according to ITEM 32 characterized in that the alkaline compound comprises calcium hydroxide.

ITEM 34. Process according to ITEM 32 or 33, characterized in that the stirring and the density of suspension (B’) are adjusted in order to avoid the appearance of a calcium phosphate gel having a viscosity of at least 200 cps.

ITEM 35. Process according to any of ITEMS 32-34 characterized in that the step of addition of the alkaline compound comprising calcium and hydroxide ions is carried out at a temperature of more than 40°C, or of at least 45°C, or of at least 50°C, and/or at most 90°C. ITEM 36. An adsorbent material for removal of contaminants from an effluent, such as water or gas effluent, comprising :

- an hydroxyapatite composite according to any of ITEMS 1-20 & 20’.

ITEM 37. An adsorbent material for removal of contaminants from an effluent, such as water or gas effluent, comprising :

- two or more hydroxyapatite composites according to Claims 1-20 & 20’, wherein the activated carbons in the hydroxyapatite composites are different. ITEM 38. An adsorbent material for removal of contaminants from an effluent, such as water or gas effluent, comprising :

- a blend of a hydroxyapatite without activated carbon and at least one hydroxyapatite composite comprising at least one activated carbon according to any of Claims 1-20 & 20’.

ITEM 39. Use of the hydroxyapatite composite of any of the ITEMS 1-20 & 20’ or of the adsorbent material of any of ITEMS 36-38 for purifying a substance comprising one or more contaminants such as a water or gas effluent, or for removing at least a portion of one or more contaminants from a water or gas effluent, preferably from a water effluent, particularly removing cations such as Hg cations, and/or oxyanions such as those of Se, As and/or B from a water effluent, comprising contacting the hydroxyapatite composite with the substance or effluent to remove at least a portion of the one or more contaminants.

ITEM 40. Use of the hydroxyapatite composite of any of the ITEMS 1-20 & 20’ or of the adsorbent material of any of ITEMS 36-38 for removing at least a portion of Hg, particularly Hg cations from a water effluent, wherein the hydroxyapatite composite comprises at least one activated carbon.

ITEM 41. Use of the hydroxyapatite composite of any of the ITEMS 1-20 & 20’ or of the adsorbent material of any of ITEMS 36-38 for removing at least a portion of selenium oxyanions from a water effluent, wherein the hydroxyapatite composite comprises activated carbon.

ITEM 42. Use of the hydroxyapatite composite of any of the ITEMS 1-20 & 20’ or of the adsorbent material of any of ITEMS 36-38 for removing at least a portion of boron ions such as borate from a water effluent, wherein the hydroxyapatite composite comprises at least one activated carbon.

ITEM 43. Use of the hydroxyapatite composite of any of the ITEMS 1-20 & 20’ or of the adsorbent material of any of ITEMS 36-38 for removing at least a portion of As oxyanions from a water effluent, wherein the hydroxyapatite composite comprises at least at least one activated carbon. ITEM 44. A method for purifying a substance comprising one or more contaminants such as a water or gas effluent, or for removing at least a portion of one or more contaminants from a water or gas effluent, preferably from a water effluent, particularly for removing cations such as Hg cations, and/or oxyanions such as those of Se, As and/or B from a water effluent, the method comprising contacting the hydroxyapatite composite of any of the ITEMS 1-20 & 20’ or the adsorbent material of any of ITEMS 36-38 with the substance or effluent to remove at least a portion of the one or more contaminants.

EXAMPLES

The examples, the description of which follows, serve to illustrate the invention.

In these examples the pH measurements were made using a WTW Sentix 41 electrode (pH 0-14, temperature: 0 °C-80 °C), a pH meter WTW pH3l 10.

The calibration of the equipment was made using three buffer solutions: at pH 4.0 (batch Dulco test-0032) Prominent, a WTW pH 7.0 (WTW D-82362) and at pH 10.01 Hach (cat 27702). Note: If multiple sample measurements were to be made with the same electrode, the electrode was rinsed with deionized water between each measurement.

The measurement of the residual water was performed using an infrared analyser Ref. MA150C from Sartorius. For this, 1.0 to 2.0g of sample are dried at 105 °C till a constant weight is obtained during at least 5 minutes.

The particle size measurement was carried out on a Beckman Coulter LS 230 laser diffraction particle size analyser (laser of wavelength 750 nm) on particles suspended in water and using a size distribution calculation based on Fraunhofer diffraction theory (particles greater than 10 pm) and on Mie scattering theory (particles less than 10 pm), the particles being considered to be spherical.

The BET specific surface area was determined by gas adsorption on a Micromeritics ASAP2020 machine. Before the analysis, the samples (0.7 to 1 g) are pretreated under vacuum at 250°C until a stable vacuum of 4-5 pbar has been achieved. The measurements were carried out using nitrogen as adsorbent gas at 77°K via the volumetric method, according to the ISO 9277: 2010 standard (Determination of the specific surface area of solids by gas adsorption - BET method). The BET specific surface area was calculated in a relative pressure (R/R0) range varying from around 0.05 to 0.20.

Example 1 (not in accordance with the invention) la. Preparation of hydroxyapatite material (without additive)

In this example, a hydroxyapatite material HAP1 was made under similar conditions as those described in example lb of WO2015/173437 patent application. The process used two steps as illustrated in FIG. 1, except that the additive is not added in this synthesis. In the first step, limestone was dispersed in water at 20-25°C in a 3-liter reactor (with baffles). Then H ₃ PO ₄ (75%) was added to this suspension and the mixture was stirred at 400 rpm using a 4-blade impeller. The first step used an overall Ca/P molar ratio of about 1. The goal of this first step was to attack the limestone to make a brushite type structure. At the end of the addition of acid, the second step was initiated by heating the mixture up to about 50°C. A 25 wt% suspension of Ca(OH) ₂ was then added to maintain the pH of the suspension at a maximum 8.9. The second step used an overall Ca/P molar ratio of about 1.67. The goal of this second step was to convert the brushite type structure created in the first step to a hydroxyapatite structure in the second step. The reaction time was 120 minutes (2.0 hrs). After the reaction time, the suspension was continually stirred at half the stirring speed than was used in the first step to allow it to cool down to 20-25°C.

The final solid content in aqueous suspension was 18% by weight (solid weight reported to total weight of the aqueous suspension).

Another hydroxyapatite sample HAP2 (without additive) was made similarly to the sample HAP1, except in a baffled 5-L reactor with a rotation speed of 700 rpm. The temperature of the second step was 50°C.

Another hydroxyapatite sample HAP3 (without additive) was made similarly to the sample HAP1, except in a baffled 200-L reactor with a rotation speed using l5Hz. The temperature of the second step was 50°C.

lb. Porosity and particle size after drying of the hydroxyapatite material (without additive)

The porosity characteristics were determined after a heat treatment at 110 °C under vacuum overnight (about 16 hours). The BET specific surface area was determined by gas adsorption on a Micro meritics ASAP2020 machine. Before the analysis, the samples (0.7 to 1 g) are pretreated under vacuum at 1 l0°C until a stable vacuum of 4-5 pbar has been achieved. The measurements were carried out using nitrogen as adsorbent gas at 77°K via the volumetric method, according to the ISO 9277 : 2010 standard (Determination of the specific surface area of solids by gas adsorption - BET method). The BET specific surface area was calculated in a relative pressure (P/PO) range varying from around 0.05 to 0.20.

The mean particles size D50 was also measured. The mean diameter D50 is the diameter such that 50 % by weight of the particles have a diameter less than said value. The particle size measurement was carried out on a Beckman Coulter LS 230 laser diffraction particle size analyser (laser of wavelength 750 nm) on particles suspended in water and using a size distribution calculation based on Fraunhofer diffraction theory (particles greater than 10 pm) and on Mie scattering theory (particles less than 10 pm), the particles being considered to be spherical.

The results can be found in TABLE 2.

TABLE 2

A picture on SEM microscope, given on FIG. 3 (500x), shows that the obtained particles (example 1) without additive are covered with plate-like crystallites.

Example 2 (in accordance with the invention)

Hydroxyapatite composite with activated carbon

2.a Selection of activated carbon for removal of selenium and mercury

Different activated charcoal powders (“A.C.”) have been identified as potential candidates according to different origins and suppliers (see TABLE 3). TABLE 3

The activated carbons were all powdered (for ease and feasibility of production) from different companies. They provided different pH when dispersed at 0.3 wt% in deionized water. These activated carbons were Pulsorb C, Pulsorb FG4, Norit® GLZ50, PTI’s Milled Classified coarse (hereinafter “PTI”), Anticromos®, Organosorb® 200-1, Organosorb® 20, and Mersorb®.

The activated carbons were tested for their efficiency in removing selenium, in particular in selenate form, and mercury. The activity of these 6 activated carbons was studied on a synthetic water concentrated in selenium - 1.2 ppm selenate (TABLE 4) using 0.5 wt% of the different activated carbons (about 0.15g in 30 mL of water) with a time of contact of 1 hour.

TABLE 4 : Efficiency of various activated carbons in removing selenate

The activity of the various activated carbons was also studied on synthetic water concentrated in mercury - 1.2 ppm HgCl ₂ (TABLE 5) using 0.5 wt% of the different activated carbons (about 0.25 g in 50 mL of water) with a time of contact of 1 hour.

TABLE 5 Efficiency of various activated carbons in removing mercury

The efficacy tests on selenium and mercury in particular (see TABLES 4 & 5) showed that the 6 activated carbons provided excellent results for removal of synthetic mercury. With respect to Se removal from synthetic water, two of the six activated carbons, , namely Pulsorb C and Milled classifield coarse of the Powder Technology Inc. brand labelled“PTI”, were shown to be superior to the other four (especially for selenates). Both of these activated carbons were were to make samples of hydroxyapatite composites.

However, due to the relatively acidic pH of the PTI activated carbon, which may have an impact on the apatite structure and the comparatively more advantageous price of Pulsorb C, the choice was made to use the hydroxyapatite composite made with Pulsorb C activated carbon for testing on removal of key elements from several industrial waters.

2.b. Two-step Synthesis of hydroxyapatite composite with activated carbon “BHAP”

Some samples of hydroxyapatite composite with activated carbon were made using Pulsorb C from Chemviron as the source of activated carbon and labelled“BHAP-C”. The proportion of activated carbon in the apatite composite ranged from 5% to 20% by weight.

A sample was made using the PTI activated carbon and labelled“BHAP- PTI”. The proportion of activated carbon in this apatite composite was 20% by weight.

A sample was made using the Mersorb® activated carbon and labelled

“BHAP-Mersorb®”. The proportion of activated carbon in this apatite composite was 10% by weight.

A sample was made using the Organosorb® 20 activated carbon and labelled“BHAP-Organosorb®”. The proportion of activated carbon in this apatite composite was 10% by weight.

The preparation of the composite samples with activated carbon (BHAP) was carried out in a similar manner as in the Example 1 , except that the activated carbon was added during the synthesis of the hydroxyapatite during the lime addition step (2 ^nd step) after the pH had risen to about 8-9 and after the reaction medium was heated to +/- 50 °C. This is illustrated in FIG. 1. The activated carbon was added in the form of a powder. Three types of reactors were used: a baffled 3-L reactor with a rotational speed of 400 ppm and 4-blade stirrer; a baffled 5-L reactor with a rotational speed of 700 ppm and with 4-blade stirrer; and a 200-L reactor with two 3 -blades stirrers operated at 17 Hz rotational speed. No significant change during the synthesis of the composites (compared to the synthesis as described in Example 1) is noted apart from this addition of activated carbon during the pH plateau in the 2 ^nd step.

The solid portion of the suspension in the second step remained the same, at about l8%-24wt% by weight. The pH used for the making of the composite samples was similar to that of apatite without additive, namely a range between pH 6.5 and 12, and preferred being maintained between 8 and 9. For the BHAP samples, the temperature for the first step was 20°C and the temperature for the second step was maintained at 50°C. The synthesis conditions are reported in TABLE 6.

TABLE 6

* Theorical content of activated carbon in the composite

These BHAP composite samples were analyzed by X-Ray, porosity, and their efficacy for removal of specific elements from water was tested.

2c. Porosity and particle size

The porosity characteristics of the BHAP composite samples are reported in TABLE 7, as well as the Pulsorb C, PTI, Mesosorb®, Organosorb® 20 activated carbons and the HAP samples (without additive) for comparison purposes.

TABLE 7

* Theorical content of activated carbon in the BHAP composites It was noted that the hydroxyapatite composite samples made with activated carbon have a higher pore volume and BET surface area than the hydroxyapatite samples made without additive.

For the size determination, a median of 35 to 49 pm (TABLE 7) and an average of 38 to 48 pm are observed for BHAPs made with Pulsorb C activated carbon. These values vary according to the content of activated carbon. It is also noted that with the use of different activated charcoal, i.e., the D50 can reach up to 58 pm.

2d, Composition of BHAP composite

The compositions of some of the BHAP samples were determined via

TGA analysis and are reported in TABLE 8.

TABLE 8

** actual wt% measured by TGA analysis based on dry matter 2e. Comparison of BHAP composite versus physical blend of activated carbon and HAP (without additive)

The activated carbon Pulsorb C was added to the composite as explained above during the synthesis of hydroxyapatite. For comparison, a physical blend (Blend) by mixing activated carbon (Pulsorb C) with an already- formed hydroxyapatite (HAP without additive) was made to obtain 5 wt% activated carbon with hydroxyapatite.

Activated charcoal release tests were performed in a plastic container to find out that the activated carbon was well incorporated into the hydroxyapatite structure in the composite sample BHAP-C5 containing 5 wt% activated carbon. The BHAP-C5 was diluted in water and stirred at 10 rpm for 5 hours.

As a control, the same test was also carried out on a synthesized HAP in which a similar proportion of activated carbon (5 wt%) was mixed. Both suspensions in water had similar pH values: pH=7.1 for the BHAP- C5 composite and pH=7.4 for the blend.

FIG. 2 shows a very marked release of activated carbon, bonded to the walls of the container, labelled“mixture”, while nothing is noticeable for the container, labelled“Composite”.

Additionally, a decantation test was performed in which the two aqueous suspensions were left to decant in a glass beaker. A clear delimitation between water and composite sample BHAP-C5 was observed for a showing of a normal decantation. Unlike the suspension of the composite sample BHAP-C5, the decanting with the suspension made with the blend was very poor due to the release of fine particles of activated carbon in the blend suspension.

This experiment demonstrates to the non- feasibility of synthesis of the composite by simple physical mixing of the activated carbon with the already- formed hydroxyapatite in solid form. This test also shows the advantage of embedding or incorporating the activated carbon into the hydroxyapatite during its synthesis. It provides a much more stable material which does not release the additive when in use in an aqueous solution particularly when it is intended to perform as an adsorbent for removal of contaminants from water.

2f. SEM Analysis

A picture on SEM microscope for hydroxyapatite composite made with 20 wt% activated carbon (BHAP-C20) is given on FIG. 4 (500x) and compared with the SEM picture FIG. 3 (500x) obtained for the hydroxyapatite particles without additive (example 1). The hydroxyapatite particles in the composite BHAP-C20 in FIG. 4 maintained their plate-like crystallites, similar to what was observed with the HAP without additive (see FIG 3).

The SEM analysis reveals two grains populations perceived by chemical contrast (apatite + activated carbon). Since the two populations, of different densities, do not separate in water (as explained above), there seems to be presence of cohesive forces for the two populations remaining linked to each other. Without wishing to be bound by this theory, it is believed that there is formation of solid bridges which maintain the composite structure intact even when submerged and moved through water, because the release of activated carbon is either nonexistent or if it exists it is very weak.

2g. Efficiency for adsorption of inorganic contaminants from water

The effectiveness of the composite BHAP with activated carbon was confirmed but variable depending on the inorganic contaminants to be removed from water, the initial concentration of these contaminants and the water matrices (as there were different speciations in the actual industrial samples compared to the synthetic waters). The description of the various industrial water samples WW1 to WW4 are provided in TABLE 9.

TABLE 9

In the efficacy tests, a suspension of 5 wt% of the composite or HAP samples were used and for control, 0.5 or 1 wt% of activated carbon was used.

The efficacy of the BHAP (composites with activated carbon) was measured with respect to Hg, B, Se and As removal from synthetic waters and from 3 of the wastewater samples WW1 to WW3. Results are provided in

TABLE 10 (for Hg), TABLE 11 (for B), TABLE 12 (for Se), and TABLE 13 (for As).

Test on Mercury removal:

The four types of activated carbon Pulsorb C, PTI, Mersorb® and

Organosorb® 20 excelled at capturing mercury, as it was demonstrated with tests carried out on synthetic water and one type of wastewater WW2. All tests show almost total efficacy (greater than 99%).

Some results are marked "> 95 %" due to a concentration that was too low and below the limit of detection of the analytical device, these samples were not passed in ICP-MS but in view of the other results they would appear to be of the same order.

Moreover, while the activity of the hydroxyapatite material without additive (HAP) was very poor (2.3%), the activity of the composites with activated carbon (BHAP) was very similar to that of activated carbon, with reductions of more than 99%, whatever the water matrix.

TABLE 10 - Test on Hg removal

Test on Boron removal:

Since the effectiveness of apatite on this metal was limited (on the order of 12- 23% reduction), the efficacy of the BHAP composite was comparatively much better (between 80 and 90% on the same wastewater sample WW3) and even greater than the reduction obtained with the activated carbon alone (68%). TABLE 11 - Test on boron (B) removal

Test on Se removal:

Concerning selenium, the impact of matrix, but especially of speciation (selenite versus selenate) was much more felt. Indeed, even if the four activated carbons (Pulsorb C, PTI, Mersorb® and Organosorb® 20) were very effective on removing selenate from synthetic water (greater than 97%), the BHAP composites were less effective, with % removal varying between 25 and 90%, depending mainly on the amount of activated carbon used and the initial concentration of Se, as well as the type of activated carbon used in the formation of the composite. However, the BHAP composites remain more effective than the hydroxyapatite HAP (alone without additive).

TABLE 12 (below) showed an increase in the metal removal (observed especially for selenates) when the amount of activated carbon in the

hydroxyapatite composite was increased. This difference was not very important for selenium of water sample WW 1 a,b,c,d due to the possibility of Se speciation rather in the form of selenites which should be captured by the hydroxyapatite and not by the activated carbon additive in the composite (0% adsorption in this wastewater matrix).

The tests on industrial waters provided a view of the impact of the matrix on % removal, as the results obtained for synthetic and actual wastewater samples were quite different. While one of the activated carbons had a very good removal activity on selenium (above 93% removal), the other activated carbon had no activity. The composite made with the effective activated carbon produced quite satisfactory results (up to 90% and down to 0.008ppm Se remaining in the water), while the composite made from the ineffective activated carbon resulted in a removal from 15 and 80% at initial water concentrations (with final concentrations between 0.23 and 0.18 ppm). The hydroxyapatite (without additive) had a removal % between 9 and 19% (decreasing to 0.21 ppm Se). It is believed that the very different results were due to the fact that the tested waters had different initial concentrations in Se and difference in selenite / selenate contents and their proportions were unknown. The presence of selenites therefore played a role on the removal Se % observed and resulted in different effectiveness for these compounds on the part of the activated carbons tested.

TABLE 12 - Test on Se removal

Test on As removal:

Very little capture of As from the BHAP composites was observed. This was not surprising considering that the HAP hydroxyapatite alone (removal of less than 20%) as well as the activated carbon has very little activity on arsenic removal from wastewater (see WW3). TABLE 13 - Test on As removal

2h. Efficiency for adsorption of organic contaminants from water: test for two target organic molecules phenol and 2,7-dihydroxynaphtalene

The efficacy of two composites with activated carbon (BHAP-C16.7 and

BHAP-PTI20) made according to Example 2 and two hydroxyapatite samples without activated carbon (HAP4 and HAP5) made according to example 1 was measured with respect to removal of two targeted organic compounds: phenol removal and 2,7-dihydroxynaphtalene (also known as 2,7-naphtalenediol) from synthetic waters each containing one of the target compounds. HAP4 was made like in Example 1 with a 50°C temperature in the second in the 5-L reactor, and HAP5 was made like in Example 1 with a 50°C temperature in the second step in the 200-L reactor. These target compounds may be found in water effluents originating from, but not limited to, pharmaceutical industry, oil & gas exploration, refining, and metallurgic industry.

In the efficacy tests for these target organic compounds, a suspension of 5 wt% of the BHAP and HAP samples (for example 50 g of BHAP or HAP particles mixed in 1 liter of synthetic water to be treated) was stirred with a laboratory magnetic stirrer. The synthetic waters contained about 16 ppm and 160 ppm of each target compound. The treated solution was sampled before the

BHAP or HAP particles were suspended and after one hour of contact with the BHAP or HAP particles, filtered through a 0.45pm membrane. The samples of the solution were analyzed using TOC kits by choosing the kit according to the concentration range (30-300 ppm for high / 3-30ppm for low content).The results of initial and final TOC concentrations before and after contact with the particles and filtration are shown on TABLE 14.

TABLE 14 : % removal efficacy of two target organic compounds starting from two initial concentrations.

The HAP, BHAP and activated carbon materials were more efficient with regard to removal at the higher initial concentration of the target organic molecules. Indeed the more molecules in solutions, the less limited by diffusion the adsorption should be, hence more efficient. However, it was surprisingly noted that, if the trend on the HAP and activated carbon was a better absorption on dihydroxynaphthalene than on phenol, it was the opposite for the BHAP composites with activated charcoal.

2i. Adsorption test for BHAP on water effluent containing polycyclic aromatic hydrocarbons (PAHs) from a pyrometallurgic process

The efficacy of a composite with activated carbon (BHAP) made according to Example 2 and containing 10 wt% activated carbon [BHAP-ClOa] was measured with respect to removal of polycyclic aromatic hydrocarbons (PAHs) from a water effluent originating from a pyrometallurgic process.

In the efficacy tests for these target organic compounds, BHAP particles were added to a stirred vessel which received the water effluent to reach an equivalent suspension of 5 wt% BHAP in water. The water effluent at the inlet and outlet of the vessel was sampled and filtered through a 0.45qm membrane. The water samples were analyzed using a HPLC technique using mass spectroscopy (MS) detection for the 16 priority compounds listed by US EPA (Naphthalene, Acenaphthylene, Acenaphthene, Fluorene, Phenanthrene, Anthracene, Fluoranthene, Pyrene, Benz[a]anthracene, Chrysene,

Benzo[b]fluoranthene, Benzo[k]fluoranthene, Benzo[a]pyrene, Indeno[ 1,2,3- cdjpyrene, Dibenzo[a,h]anthracene and Benzo[ghi]perylene). The test was repeated on the water effluent for 11 days, labelled Samples 2i-l to 2i-l 1. The results of overall PAHs removal based on average daily concentrations in wastewater streams at the inlet and outlet of the vessel while the BHAP was added to the vessel are shown on TABLE 15.

TABLE 15 : Removal efficacy of 16 U.S.E.P.A. PAH priority compounds in a wastewater stream from a pyrometallurgic process

2j. Adsorption test for BHAP on water effluent containing polycyclic aromatic hydrocarbons (PAHs) from a wet scrubber process

The efficacy of a composite with activated carbon (BHAP) made according to Example 2 and containing 15 wt% activated carbon [BHAP-C15] was measured with respect to removal of polycyclic aromatic hydrocarbons (PAHs) from a water effluent originating from a wet scrubber process. The test in this example was carried out in a similar manner in for Example 2i. The water samples were analysed using a HPLC technique using mass spectroscopy (MS) detection for the 16 priority compounds listed by US EPA. The test was repeated on the water effluent for 3 consecutive days, labelled Samples 2j-l to 2j-3. The results of overall PAHs removal based on average daily concentrations (ppb) in wastewater streams at the inlet and outlet of the vessel while the BHAP was added to the vessel are shown on TABLE 16.

TABLE 16 : Removal efficacy of 16 U.S.E.P.A. PAH priority compounds in a wastewater stream from a wet scrubber process

Example 3 (in accordance with the invention)

Hydroxyapatite composite with activated carbon made from brushite 3. a. One-step Synthesis of hydroxyapatite composite with activated carbon “BHAP-BRU” from brushite and calcium hydroxide

A sample of hydroxyapatite composite with activated carbon labelled “BHAP-BRU” was made from brushite (CaHsOeP, no. AC389830010 from Acros), calcium hydroxide and Pulsorb C from Chemviron as the source of activated carbon. The proportion of activated carbon in the resulting apatite composite was 10% by weight.

The preparation of the composite sample“BHAP-BRU” was carried out as follows. About 1,062 g of a suspension of Ca(OH) ₂ (25wt%) was added to a mass of 3,973 g of a suspension of brushite (23.4wt%) heated to +/- 50 °C in a baffled 5-L reactor with a rotational speed of 700 ppm and with 4-blade stirrer. The activated carbon Pulsorb C (90g) - see TABLE 3 - was added at the same time as the lime addition was started at the beginning of the synthesis of the hydroxyapatite composite.

The solid portion of the suspension after 280 minutes was about 21.2 wt% apatite by weight. The pH used for the making of the composite sample started at pH 7.09 to end at a pH of 1 1.2. For this composite sample, the temperature for the synthesis was maintained at about 5l-52°C. 3b. Cationic standard test for performance evaluation on selected metallic cations

6b.1 Preparation of mother solutions for each metallic cation:

A mother solution for each of the metals from the following metal salts containing M = Cd, Cr, Cu, Mn, Ni, Pb, Zn, Hg, as shown in TABLE 17 is prepared by adding the salt of each metal in deionized water to reach 1 g M/L content.

TABLE 17

* MW = molecular weight

3 b.2 Preparation of a standard solution for the cationic standard test:

A standard solution containing 5 mg/L (5 ppm) of cations for Cd, Cr, Cu, Mn, Ni, Pb, Zn and 1 mg/L (1 ppm) Hg cation was prepared from the 7 mother solutions as follows: with the aid of a micropipette, add 5 mL of each of the mother liquors containing Cd, Cr, Cu, Mn, Ni, Pb, Zn and 1 mL of the mother liquor containing Hg into a flask and add water to reach a total volume of 1 liter. 3b.3 Measure of the dry mater content for each material sample for the cationic standard test:

- Dry approximately 2-3 g of a composite sample for 3 hours, stirring every 30 minutes in an oven at 80°C to obtain a representative homogeneous sample ; and

Determine the dry matter content (wt% DM) of the dried sample using a moisture meter such as a thermal balance sold by Sartorius. 3b.4 Steps for the cationic standard test on performance evaluation : - Take a lOO-ml initial sample from the standard solution at time 0 (before adding the apatic material to start the test)

- Measure the mass of the wet material sample (not dried) in order to achieve a suspension containing 0.03 wt% of dry matter in a given volume of the standard solution in a container using the following formula:

- , , , , , , , 0.03 wt% _* volume of standard solution (mL)

Mass (wet sample) (g) = - :

- Shake the suspension mechanically for 1 hour in the container at 250 rpm;

- Take a lOO-ml sample from the suspension after 1 hour and filter it on a 0.45- pm filter to remove solids;

- Stabilize the two lOO-ml samples taken at time = 0 and time = 1 hour by adding 1 ml of concentrated nitric acid (65% HN03); and

- Send to ICP-OES for analysis to determine the contents of metals: Cd, Cr, Cu, Mn, Ni, Pb, Zn, Hg.

3b.5 Method ICP-EOS :

Scandium (as internal standard) and optionally gold (to stabilize Hg when Hg determination is required) to an aliquot of each water sample which is slightly acidified with concentrated nitric acid. The solution is then brought to volume with ultrapure water in order to obtain a 5 -time dilution. The final diluted solution typically contains 2% to 5% HN03, 1 or 2 mg/l scandium and, where appropriate, 1 or 2 mg/l gold.

The determination of contents of specific elements such as Al, As, B, Ba, Ca, Cd, Co, Cr, Cu, Fe, Ga, Hg, K, Mg, Mn , Mo, Na, Nb, Ni, P, Pb, Sb, Se, Sn, Ta, V, W and Zn in the water samples are done by ICP-OES (Inductively

Coupled Plasma - Optical Emission Spectrometry) with axial and observation of the plasma and CCD detector. The solutions to be measured are nebulized and transported in the plasma with argon as a carrier gas. In the plasma, the different elements emit light with a wavelength specific to each element and with an intensity directly proportional to their concentration.

The measurements of the emitted light intensity by each element used in the standard test are evaluated against an external calibration established between 0 and 5 mg/l for each element to be measured. This calibration consists of seven (7) solutions: a calibration blank and six (6) solutions of increasing

concentrations (0.1 mg/l, 0.2 mg/l, 0.5 mg/l, 1 mg/l, 2 mg/l and 5 mg/l of each element). All the calibration solutions also contain the same concentration of HNO3, scandium and gold as the diluted sample solutions.

3c. Results of the cationic standard test for the composite BHAP-BRU

The cationic standard test (see Section 6.b) was carried out with the composite sample BHAP-BRU whose preparation is described in section 3. a. The % removal for the 7 metallic cations during the cationic standard test are provided in TABLE 18.

For comparison, the same cationic standard test was carried on a sample of a BHAP-C10 composite with activated carbon (10 wt% Pulsorb C) made using the 2-step method starting from calcium carbonate and phosphoric acid in I ^st step and calcium hydroxide in 2 ^nd step (similar to Example 2) and a HAP sample (without activated carbon) also using the 2-step method.

TABLE 18

^V1 Composite with activated carbon (10 wt% Pulsorb C) using the 2-step method

v ^u Hydroxyapatite produced with the 2-step method

As observed for both of composites with activated carbon, the

performance for removal of Hg, Ni, and Zn was improved compared to the apatite material (without activated carbon). In addition, the performance in Cd, Cr, Zn, Ni removal was increased with the composite BHAP-BRU which was prepared with the one-step method from brushite, compared to the composite BHAP-C10 which was prepared with the two-step method from calcium carbonate and phosphoric acid using the same amount of Pulsorb C activated carbon.

3d. Anionic standard test for performance evaluation on selected metallic anions

6d.l Preparation of mother solutions for each metallic anion:

A mother solution for each of the metals from the following metal salts containing M = Arsenic(V), Molybdum(VI), Selenium(VI) and Vanadium(V), as shown in TABLE 19 was prepared by adding the salt of each metal in deionized water to reach 1 g M/L content.

TABLE 19

* MW = molecular weight

3d.2 Preparation of a standard solution for the anionic standard test:

A standard anionic solution containing 1 mg/L (1 ppm) of anions for As (V), Mo (VI), Se (VI) and V (V), was prepared from the 4 mother solutions as follows: with the aid of a micropipette, add 1 mL of each of the 4 mother liquors containing As (V), Mo (VI), Se (VI) and V (V) into a flask and add water to reach a total volume of 1 liter.

3d.3 Measure of the dry mater content for each material sample for the standard test:

- Dry approximately 2-3 g of a composite sample for 3 hours, stirring every 30 minutes in an oven at 80°C to obtain a representative homogeneous sample ; and

Determine the dry matter content (wt% DM) of the dried sample using a moisture meter such as a thermal balance sold by Sartorius.

3d.4 Steps for the anionic standard test on performance evaluation :

- Take a lOO-ml initial sample from the standard anionic solution at time 0 (before adding the apatic material to start the test)

- Measure the mass of the wet material sample (not dried) in order to achieve a suspension containing 0.5 wt% of dry matter in a given volume of the standard solution in a container using the following formula:

- , , , , , , , 0.5 wt% _* volume ofstandard solution (mL)

Mass (wet sample) (g) = - wt%DM · - Shake the suspension mechanically for 1 hour in the container at 250 rpm;

- Take a lOO-ml sample from the suspension after 1 hour and filter it on a 0.45- pm filter to remove solids;

- Stabilize the two lOO-ml samples taken at time = 0 and time = 1 hour by adding 1 ml of concentrated nitric acid (65% HN03); and

- Send to ICP-OES as described in Section 6b.5 for analysis to determine the contents of metals: As (V), Mo (VI), Se (VI) and V (V).

3e. Results of the anionic standard test for the composite BHAP-BRU

The anionic standard test (see Section 3b) was carried out with the composite sample BHAP-BRU whose preparation is described in section 3a. The % removal for the 4 metallic anions during the anionic standard test are provided in TABLE 20.

For comparison, the same anionic standard test was carried on a HAP sample (without activated carbon) made using the 2-step method. TABLE 20

v ^u Hydroxyapatite produced with the 2-step method

The performance for As (V) removal with the composite BHAP-BRU with activated carbon made with the l-step method was improved compared to the hydroxyapatite material HAP (without activated carbon).

The disclosure of all patent applications, and publications cited herein are hereby incorporated by reference, to the extent that they provide exemplary, procedural or other details supplementary to those set forth herein.

Should the disclosure of any of the patents, patent applications, and publications that are incorporated herein by reference conflict with the present specification to the extent that it might render a term unclear, the present specification shall take precedence.

In the present application, where an element or component is said to be included in and/or selected from a list of recited elements or components, it should be understood that in related embodiments explicitly contemplated here, the element or component can also be any one of the individual recited elements or components, or can also be selected from a group consisting of any two or more of the explicitly listed elements or components. Any element or component recited in a list of elements or components may be omitted from such list.

Further, it should be understood that elements, embodiments, and/or features of processes or methods described herein can be combined in a variety of ways without departing from the scope and disclosure of the present teaching, whether explicit or implicit herein.

Accordingly, the scope of protection is not limited by the description set out above, but is only limited by the claims which follow, that scope including all equivalents of the subject matter of the claims. Each and every claim is incorporated into the specification as an embodiment of the present invention. Thus, the claims are a further description and are an addition to the preferred embodiments of the present invention.

While preferred embodiments of this invention have been shown and described, modifications thereof can be made by one skilled in the art without departing from the spirit or teaching of this invention. The embodiments described herein are exemplary only and are not limiting. Many variations and modifications of systems and methods are possible and are within the scope of the invention.