A particulate material comprising a hydroxyapatite and a metal sulfide and its use for removing contaminants from a fluid

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application claims priority to European application No.

18214569.8 filed December 20, 2018, the whole content of this application being incorporated herein by reference for all purposes.

TECHNICAL FIELD

The invention relates to a particulate material comprising a hydroxyapatite and a metal sulfide, and processes for preparing it. It also relates to an adsorbent or reactant or a suspension comprising the particulate material and the use of the particulate material for removing contaminants from a fluid, particularly metals such as mercury.

BACKGROUND ART

It is common to treat various sources of waste effluents in order to remove contaminants. Examples of sources of waste effluents for treatment include water sources such as 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.

Wastewater treatment is one of the most important and challenging environmental problems. For example, in the 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.

It is particularly 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 FeS2 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.

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 mercury as well as cationic species of contaminating elements.

It is thus useful to develop a particulate 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 and in particular Hg. SUMMARY OF INVENTION

Accordingly, one aspect of the present invention relates to a

hydroxyapatite-based particulate material which can be effective in removing contaminants such as metals from a fluid. This hydroxyapatite-based particulate material can simultaneously remove a large variety of metallic contaminants from this fluid.

To enhance the sorption of the hydroxyapatite-based particulate material towards a large spectrum of metallic contaminants, it has been found that the hydroxyapatite activity can be supplemented by adding a metal sulfide to yield a hydroxyapatite-based particulate material with an improved adsorption affinity and/or efficiency with respect to metals, and particularly mercury, such adsorption affinity and/or efficiency being the same or greater than that of an unmodified hydroxyapatite structure, that is to say, which is not modified with a metal sulfide.

In some preferred embodiments, the metal sulfide may be deposited on the hydroxyapatite, preferably in the form of particles, to form a modified hydroxyapatite material. In such instance, the metal sulfide is preferably formed from two precursors/sources. One precursor provides the metal‘Me’ in the metal sulfide and the other precursor provides the‘sulfide’ in the metal sulfide. By “deposited”, it is meant that the metal sulfide may be coated onto the

hydroxyapatite surface, or otherwise associated with the hydroxyapatite structure via cohesive forces.

In other preferred embodiments, the metal sulfide may be incorporated or embedded into the hydroxyapatite, preferably in the form of particles, to form a hydroxyapatite composite.

In alternate embodiments, the metal sulfide may be physically mixed with the hydroxyapatite, preferably in the form of particles, to form a hydroxyapatite mixture. In such instance, the metal sulfide is preferably mixed‘as is’.

In instances of composite or mixture, the metal sulfide is preferably used ‘as is’ and may be sourced from a commercially available metal sulfide or may be formed separately before being mixed with, incorporated or embedded into the hydroxyapatite.

One advantage of the present invention is improving the sorption affinity of a hydroxyapatite-based particulate material for at least mercury that would otherwise not be adsorbed or poorly adsorbed from a contaminated effluent by a hydroxyapatite without metal sulfide. In particular embodiments, such material comprising hydroxyapatite and a metal sulfide enhances the removal efficiency of mercury, while not negatively impacting the removal efficiency of other metals already provided by the hydroxyapatite.

One advantage of making a composite which embeds the metal sulfide into the hydroxyapatite or a modified hydroxyapatite which coats the metal sulfide on the hydroxyapatite is to provide a more stable material, compared to the physical mixture of hydroxyapatite and the same metal sulfide. This is particular useful when the particulate material is in use in an aqueous solution and is intended to perform as adsorbent for removal of metals, and in particular mercury, from water.

In instances when the metal sulfide could be used as a sorbent in powder form for water treatment, the inclusion of the metal sulfide as co-sorbent in the hydroxyapatite-based particulate material provides yet another advantage. While the use of a metal sulfide co-sorbent in a loose powder may offer large surface area for adsorption capacity, a loose powder needs specific and costly equipment to be removed from a treated water effluent, and solid/liquid separation problems limit reactor configurations that require incorporating large sedimentation basins or filtration.

There is therefore a benefit for a solid metal sulfide to be incorporated into or coated onto the hydroxyapatite structure to form the modified hydroxyapatite or the hydroxyapatite composite in accordance to the present invention, so the resulting material can be used in practical adsorption processes.

The modified hydroxyapatite or the hydroxyapatite composite preferably has a suitable size much larger than that of a loose powder, and these large particles are easier to separate from a treated water effluent, using a solid/liquid separation technique such as by settling than a powder.

A first aspect of the present invention relates to a particulate material comprising a hydroxyapatite and at least one metal sulfide, which includes: a mixture wherein the metal sulfide is physically mixed with the hydroxyapatite,

a composite wherein the metal sulfide is incorporated or embedded into the hydroxyapatite, and/or

a modified hydroxyapatite wherein the metal sulfide is deposited on the hydroxyapatite. In some embodiments, the particulate material includes a modified hydroxyapatite wherein the at least one metal sulfide is deposited on the hydroxyapatite.

In alternate or additional embodiments, the particulate material includes a composite wherein the at least one metal sulfide is incorporated or embedded into the hydroxyapatite.

In some embodiments, the metal in the at least one metal sulfide is selected from the group consisting of iron (Fe), cobalt (Co), manganese (Mn), nickel (Ni), copper (Cu), zinc (Zn), cadmium (Cd), lead (Pb), antimony (Sb), and any combination of two or more thereof, preferably selected from the group consisting of iron (Fe), manganese (Mn), nickel (Ni), copper (Cu), zinc (Zn), antimony (Sb), and any combination of two or more thereof; more preferably selected from the group consisting of iron (Fe), copper (Cu), zinc (Zn) and any combination of two or more thereof; most preferably selected from the group consisting of copper (Cu), zinc (Zn), and any combination thereof.

In preferred embodiments, the metal sulfide is selected from the group consisting of pyrite (FeS2, cubic), marcasite (FeS2, orthorombic), greigite (Fe3S4, cubic), smythite (FegSn, hexagonal), mackinawite (FeSi_ _x , 0<x<0.07, tetragonal), pyrrhotite (Fei_ _x S, 0<x<0.125, monoclinic and hexagonal), trolite (FeS, hexagonal), CoS, MnS, NiS, CuS (cupric sulfide), C _¾ S (cuprous sulfide), ZnS, CdS, PbS, Sb2S3, and any combination thereof; more preferably selected from the group consisting of pyrite (FeS2, cubic), mackinawite (FeSi_ _x ,

0<x<0.07, tetragonal), trolite (FeS, hexagonal), CoS, MnS, NiS, CuS (cupric sulfide), ZnS, CdS, PbS, Sb2S3, and any combination thereof.

In some embodiments, the particulate material comprises a molar ratio of sulfur to metal (S:Me) of at most 2, preferably at most 1.

In some embodiments, the particulate material comprises, based on the total weight of dry matter:

- at least 50wt%, advantageously at least 60wt%, and more advantageously still at least 70wt%, or at least 75wt% of the hydroxyapatite, preferably wherein the hydroxyapatite is a calcium-deficient hydroxyapatite, more preferably a hydroxyapatite with a Ca/P molar ratio more than 1.5 and less than 1.67; and

- a metal sulfide content from 1 to 25 wt%, preferably from 1 to 20 wt%, more preferably from 1 to 15 wt%.

A second aspect of the present invention relates to a process for making the particulate material. In an embodiment in this process for making wherein the particulate material comprises a modified hydroxyapatite wherein the at least one metal sulfide is deposited on the hydroxyapatite, the process comprises:

- making a suspension of hydroxyapatite-containing particles in water;

- contacting the hydroxyapatite-containing particles in the suspension with a precursor of the metal (Me);

- contacting the hydroxyapatite-containing particles in the suspension with a source of S ² or HS , preferably H ₂ S, NaHS or Na ₂ S, more preferably NaHS, to obtain a molar ratio S:Me which is at most 2, preferably at most 1, more preferably at most 0.85, yet more preferably at most 0.7, during or after the contacting step with said metal precursor, preferably after the contacting step with said metal precursor, to deposit the metal sulfide on the hydroxyapatite;

- separating the particles from the suspension after contacting with the source of S ² or HS ;

- washing the separated particles with water; and

- recovering the washed particles to form the modified hydroxyapatite

comprising the metal sulfide.

In the process for making the particulate material, the suspension of the hydroxyapatite-containing particles may comprise from 25 to 200 g, preferably from 50 to 150 g, of dry matter per liter of water.

In the process for making the particulate material, the precursor of the metal may comprise, or consist essentially of, a salt of the metal, preferably an inorganic salt of the metal, more preferably a chloride, nitrate or sulfate salt of the metal, yet more preferably a chloride or nitrate salt of the metal.

In the process for making the particulate material, less than 100% of the S in the source of S ² or HS may be converted to the metal sulfide.

In the process for making the particulate material, the contacting with the source of S ² or HS may be carried out after the contacting with the metal precursor, and optionally there is no separation between the two contacting steps.

The contacting step with the metal precursor and the contacting step with the source of S ² or HS may be carried about at a pH value from 4 to 10, preferably from 4 to 8.

In an embodiment in the process for making wherein the particulate material comprises the composite and wherein the at least one metal sulfide is incorporated or embedded into the hydroxyapatite, the process comprises: - providing an aqueous suspension (A) comprising particles containing 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 (A) 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 metal sulfide to the suspension (A) before the addition of the alkaline compound or to the suspension (B) during or after the addition of the alkaline compound, preferably before or during the addition of the alkaline compound, to form the composite,

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

In this process for making the particulate material, the alkaline compound comprises calcium hydroxide.

In this process for making the particulate material, providing the aqueous suspension (A) may comprise:

- mixing a source of calcium and a source of phosphate ions in water in a molar ratio that is adjusted to obtain a Ca/P molar ratio of between 0.5 and 1.5, preferably between 0.5 and 1.35, and reacting the source of calcium with the phosphate ions at a pH of between 2 and 8, in order to obtain the suspension (A) comprising particles containing the calcium phosphate compound.

A third aspect of the present invention relates to an adsorbent material for removal of contaminants, such as Al, Ag, As, B, Ba, Be, Bi, Ce, Co, Cd, Cu, Cr, Fe, Hg, Hf, La, Li, Mg, Mn, Mo, Ni, Pb, Pd, Rb, Sb, Se, Sn, Sr, Th, Ti, U, V, Y, Zn, and/or Zr, preferably Hg, from a fluid, comprising :

- the particulate material according to any embodiment described herein; or

- two or more particulate materials according to any embodiment described herein, wherein the metal sulfides are different in the two or more particulate materials; or

- a blend of a particulate hydroxyapatite without metal sulfide and at least one particulate material according to any embodiment described herein. A fourth aspect of the present invention relates to the use of the particulate material according to any embodiment described herein or of the adsorbent material in the form of particles according to the third aspect for removing from a fluid at least a portion of an element selected from the group consisting of Al, Ag, As, B, Ba, Be, Bi, Ce, Co, Cd, Cu, Cr, Fe, Hg, Hf, La, Li, Mg, Mn, Mo, Ni, Pb, Pd, Rb, Sb, Se, Sn, Sr, Th, Ti, U, V, Y, Zn, and/or Zr, preferably for removing Hg from a fluid, such as a water or gas effluent.

The use or of the method for removing at least a portion of an element from a fluid may comprise:

contacting the particulate material with said fluid for a time sufficient to remove at least 30%, preferably at least 50%, more preferably at least 70% of the element, preferably Hg, from the fluid.

The foregoing has outlined rather broadly the features and technical advantages of the present invention in order that the detailed description of the invention that follows may be better understood. Additional features and advantages of the invention will be described hereinafter that form the subject of the claims of the invention. It should be appreciated by those skilled in the art that the conception and the specific embodiments disclosed may be readily utilized as a basis for modifying methods or processes or designing other structures for carrying out the same purposes of the present invention. It should also be realized by those skilled in the art that such equivalent constructions or methods or processes do not depart from the spirit and scope of the invention as set forth in the appended claims.

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” material 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 fluid to be treated flows.

As used herein, the term“downstream” refers to a position situated in the same direction from that in which the fluid 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 105°C for at least 1 hour.

As used herein, the term“precursor of the metal” refers to a compound that is converted in the modified hydroxyapatite material to metal sulfide. For example a copper salt like copper chloride can be converted to, at least in part, copper sulfide during the making of the modified hydroxyapatite.

As used herein, the term“source of S ² or FIS” refers to a compound that is converted to a sulfide in the particulate material. For example a hydrosulfide compound like sodium hydrosulfide can be converted to, at least in part, a metal sulfide during the making of the particulate material.

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 material" denotes one material or more than one material.

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

HYDROXYAPATITE-BASED PARTICULATE MATERIAL

One aspect according to the present invention relates to a hydroxyapatite- based particulate material comprising a hydroxyapatite and at least one metal sulfide. The particulate material may include:

- a mixture wherein the metal sulfide is physically mixed with the

hydroxyapatite,

- a composite wherein the metal sulfide is incorporated or embedded into the hydroxyapatite, and/or

- a modified hydroxyapatite wherein the metal sulfide is deposited on the hydroxyapatite.

The hydroxyapatite-based particulate material is preferably in the form of particles.

In preferred embodiments, the hydroxyapatite-based particulate material 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-based particulate material 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 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.

In additional embodiments, the hydroxyapatite-based particulate material 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-based particulate material 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.

In some embodiments, the metal (Me) in the metal sulfide is a metal selected from groups 7-14 of the IUPAC Periodic Table.

In preferred embodiments, the metal Me in the metal sulfide is selected from the group consisting of iron (Fe), cobalt (Co), manganese (Mn), nickel (Ni), copper (Cu), zinc (Zn), cadmium (Cd), lead (Pb), antimony (Sb), and any combination of two or more thereof, preferably selected from the group consisting of iron (Fe), manganese (Mn), nickel (Ni), copper (Cu), zinc (Zn), antimony (Sb), and any combination of two or more thereof; more preferably selected from the group consisting of iron (Fe), copper (Cu), zinc (Zn) and any combination of two or more thereof; most preferably selected from the group consisting of copper (Cu), zinc (Zn), and any combination thereof.

As used herein, the term“MeS” for the metal sulfide is used generically and refers to any form of the metal sulfide and not limited to an equimolar formula with a S:Me=l. For example when copper is the metal Me,“MeS” may encompass CuS and/or CU2S. When antimony Sb is the metal Me,“MeS” may encompass Sb2S3. When iron is the metal Me,“MeS” may encompass the following : pyrite (FeS2, cubic), marcasite (FeS2, orthorombic), greigite (Fe3S4, cubic), smythite (FegSn, hexagonal), mackinawite (FeSi_ _x , 0<x<0.07, tetragonal), pyrrhotite (Fei_ _x S, 0<x<0.125, monoclinic and hexagonal) and/or trolite (FeS, hexagonal).

In preferred embodiments, the metal sulfide is selected from the group consisting of pyrite (FeS2, cubic), marcasite (FeS2, orthorombic), greigite (Fe3S4, cubic), smythite (FegS i 1, hexagonal), mackinawite (FeSi_ _x , 0<x<0.07, tetragonal), pyrrhotite (Fei_ _x S, 0<x<0.125, monoclinic and hexagonal), trolite (FeS, hexagonal), CoS, MnS, NiS, CuS, C112S, ZnS, CdS, PbS, Sb2S3, and any combination thereof.

The hydroxyapatite-based particulate material may comprise more than one metal sulfide MeS. For instance, the hydroxyapatite-based particulate material may comprise a first metal sulfide Me’S and a second metal sulfide Me”S, wherein Me’ and Me” are different metals.

The hydroxyapatite-based particulate material may comprise at least 1 wt%, or at least 2 wt%, or at least 3 wt% Me based on the total dry matter weight.

The hydroxyapatite-based particulate material may comprise at most 20 wt%, or at most 15 wt%, or at most 12 wt%, or at most 10 wt% Me based on the total dry matter weight of the particles.

In preferred embodiments, the hydroxyapatite-based particulate material has a metal sulfide content from 1 to 25 wt%, preferably from 1 to 20 wt%, more preferably from 1 to 15 wt%, yet more preferably from 1 to 10 wt% based on the total dry matter weight.

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

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

MIO(X0 ₄ ) ₆ Y2

In this formula, M generally represents a divalent cation (M ²⁺ ), XO4 a trivalent anionic group (XO4 ³ ) and Y a monovalent anion (U ).

Calcium phosphate hydroxyapatite Caio(P04)6(OH) ₂ crystallizes in the space group of the hexagonal system. This structure consists of a close-packed quasi-hexagonal stack of XO4 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: Ca3(PC>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.

The hydroxyapatite in the hydroxyapatite-based material may be deficient in calcium compared to a stoichiometric 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.

In preferred embodiments, the hydroxyapatite-based particulate material comprises a calcium-deficient hydroxyapatite, preferably with a Ca/P molar ratio more than 1.5 and less than 1.67.

In more preferred embodiments, the calcium-deficient hydroxyapatite may have a Ca/P molar ratio of about 1.55-1.59, while the hydroxyapatite-based particulate material may have a Ca/P molar ratio of about 1.60-1.67.

In some embodiments, the hydroxyapatite-based particulate material may comprise a calcium-deficient hydroxyapatite with a Ca/P of less than 1.67 but has an overall Ca/P molar ratio higher than the calcium-deficient hydroxyapatite.

In such instances, calcium may be and is preferably present in another form (other than the calcium-deficient hydroxyapatite) in the hydroxyapatite-based particulate material. Calcium carbonate may be present in the hydroxyapatite- based particulate material. 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 particulate material, the hydroxyapatite-based particulate material generally has an overall Ca/P molar ratio higher than the calcium-deficient hydroxyapatite present in the

hydroxyapatite-based particulate material. For that reason, in some

embodiments, even though the calcium-deficient hydroxyapatite in the hydroxyapatite-based particulate material may have a Ca/P molar ratio less than 1.67, the entire hydroxyapatite-based particulate material may have a Ca/P molar ratio equal to or more than 1.67, however it is generally not more than 1.75. 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=1.67 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.

In some embodiments, the hydroxyapatite-based particulate material 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-based particulate material 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-based particulate material 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% water or even lower.

In some embodiments, the hydroxyapatite-based particulate material 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-based particulate material 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%.

The hydroxyapatite-based particulate material 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 ).

In some embodiments, the hydroxyapatite-based particulate material is substantially free of calcium dihydroxide (i.e., less than 0.1 wt% Ca(OH) ₂ ).

In some embodiments, the hydroxyapatite-based particulate material 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 the hydroxyapatite-based particulate material may additionally contain residual compounds originating from raw materials used in its manufacture, such as: CaCf, Ca(NC>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-based particulate material may comprise, on the basis of the total dry matter weight,

- 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-based particulate material preferably has a molar ratio of S:Me which is at most twice the stoichiometric ratio of S per Me in the metal sulfide (also referred to an“equivalent” ratio), preferably which is equal to or less than the stoichiometric ratio of S per Me in the metal sulfide, more preferably at most 0.85 eq. S per metal, more preferably at most 0.7 eq. S per metal.

In some preferred embodiments according to the present invention, the hydroxyapatite-based particulate material in the form of particles comprising the metal sulfide comprises plate-like hydroxyapatite crystallites, of thickness of a few nano-meters (nm) on their surface, which may be coated by smaller particles of the metal sulfide or into which smaller particles of the metal sulfide are embedded into the hydroxyapatite. The smaller particles of the metal sulfide are likely associated with the hydroxyapatite structure via cohesive forces.

In some embodiments according to the present invention, the

hydroxyapatite-based particulate material in the form of 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 metal sulfide. These distinct types of solid particles are preferably interdispersed.

In the making of a composite, because the metal sulfide is added prior to or during the synthesis of the hydroxyapatite structure, the particles associated with the metal sulfide 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, or if the metal sulfide is released, its release is less than what would occur with a same amount of the metal sulfide not in a composite.

In some embodiments, the hydroxyapatite-based particulate material may exclude bone char.

In some embodiments, the hydroxyapatite-based particulate material may include bone char.

“Bone char” (also called“bone charcoal”) refers to a porous, black, granular material produced by charring animal bones. Its composition varies depending on how it is made. Bones (especially cow bones) are heated in a sealed vessel at up to 700 °C (1,292 °F); a low concentration of oxygen is maintained during heating, as oxygen content affects the quality of the bone char product, particularly its adsorption capacity. Most of the organic material in the bones is driven off by heat. Bone char generally contains 7-10% carbon.

In some embodiments, the hydroxyapatite-based particulate material is substantially free of carbon, i.e., less than 0.5 wt% of carbon.

In some embodiments, the hydroxyapatite-based particulate material contains less than 10 wt% of tricalcium phosphate (TCP) or preferably excludes TCP.

In preferred embodiments, the hydroxyapatite-based particulate material 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.

In some embodiments, the hydroxyapatite-based particulate material may exclude a polymer, such as may exclude chitosan and/or a polyvinyl alcohol.

In preferred embodiments, the hydroxyapatite-based particulate material is inorganic

In other embodiments, the hydroxyapatite-based particulate material contains less than 1 wt% organics.

PROCESS FOR MAKING THE HYDROXYAPATITE-BASED

PARTICULATE MATERIAL COMPRISING A METAL SULFIDE

Another aspect of the present invention relates to processes for making the particulate material comprising the hydroxyapatite and the metal sulfide. A first embodiment of the process for making the particulate material includes steps for making a modified hydroxyapatite wherein the at least one metal sulfide is coated onto the hydroxyapatite.

A second embodiment of the process for making the particulate material includes steps for making a hydroxyapatite composite wherein the at least one metal sulfide is incorporated or embedded into the hydroxyapatite.

A third embodiment of the process for making the particulate material includes steps for making a mixture wherein the at least one metal sulfide is physically mixed with the hydroxyapatite.

The process for making the particulate material may include a separation step to remove hydroxyapatite particles from a suspension fluid such as water. Hence ye process may include a dewatering step which increases the solids content. The separation may comprise for example filtration, such as, but not limited to, in a filter press, centrifuge filter, or rotating filter.

In some embodiments, the process for making the particulate material may further comprise drying the recovered material at a temperature between 50 to 180°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 recovered material such as, but not limited to, spray drying, flash drying, and/or drying in a fluidized bed.

Drying may be carried out in an inert atmosphere or in the presence of an inert gas, such as containing or consisting of nitrogen (N2).

Process for making the modified hydroxyapatite with a metal sulfide

When the particulate material comprises a modified hydroxyapatite wherein the at least one metal sulfide is deposited (coated) onto the

hydroxyapatite, an embodiment of the process for making the particulate material comprises:

- making a suspension of hydroxyapatite-containing particles in water;

- contacting the hydroxyapatite-containing particles in the suspension with a precursor of the metal (Me);

- contacting the hydroxyapatite-containing particles in the suspension with a source of S ² or HS , preferably thiourea, thioamides, thiols, ¾S, NaHS or Na2S, more preferably NaHS, during or after the contacting step with said metal precursor, to achieve a molar ratio S:Me which is at most 2, preferably at most 1, more preferably at most 0.85, yet more preferably at most 0.7; - separating the particles from the suspension after contacting with the source of S ² or HS ;

- washing the separated particles with water; and

- recovering the washed particles to form the modified hydroxyapatite

comprising a sulfide of said metal (MeS).

In some embodiments, the suspension of the hydroxyapatite-containing particles comprises from 25 to 200 g, from 50 to 150 g, of dry matter per liter of water.

It can be envisioned that two or more metal precursors may be used in the process. In an example, a first metal precursor may be added in the first contacting step and a second metal precursor is added in the second contacting step with the source of S ² or HS . Alternatively, the first and second metal precursors may be used together during the same contacting step with the hydroxyapatite-containing particles in the suspension.

If two different metals Me’ and Me” are used in the process for making the particulate material, it may be envisioned that a Me’ precursor and a Me” precursor may be added in the contacting step with the hydroxyapatite- containing particles. Alternatively, the Me’ precursor may be added in the first contacting step with the hydroxyapatite-containing particles in the suspension and the Me” precursor may be added in the second contacting step with the source of S ² or HS .

The metal precursor may be organic or inorganic.

In preferred embodiments, the metal precursor is inorganic.

In preferred embodiments, the precursor of the metal Me may comprise, or consist essentially of, a salt of the metal, preferably an inorganic salt of the metal, more preferably a chloride, nitrate or sulfate salt of the metal, yet more preferably a chloride or nitrate salt of the metal.

In some embodiments, the precursor of the metal may be used in dissolved form, in gas form, in solid form or in suspended form (such as a slurry).

In some embodiments, the process comprises adding the metal precursor in the form of a solution or a slurry to the suspension.

In preferred embodiments when the metal precursor is water-soluble, the precursor of the metal may be dissolved into water prior to adding it the suspension for contacting the hydroxyapatite-containing particles.

In some embodiments, the process for making the modified hydroxyapatite comprises adding the metal precursor in the form of a solid to the suspension. In some embodiments when the D50 particle size of the solid metal precursor is greater than 100 microns, the process for making the modified hydroxyapatite may further include grinding or milling the solid metal precursor 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, to achieve a powder which is then added to the suspension.

In some embodiments, when the metal precursor may be in the form of a powder (either sold‘as is’ or ground before use), the process for making the modified hydroxyapatite may further include sieving the powder of the Me precursor 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 Me precursor which passes through a sieve No. 170 (under ASTM El 1) 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 the suspension.

In some embodiments, the process for making the modified hydroxyapatite comprises adding the metal precursor in the form of a gas.

The source of S ² or HS used during the making of the modified hydroxyapatite may include an inorganic or organic sulfide, hydrosulfide, disulfide, or polysulfide. The source of S ² or HS preferably comprises or consists of an alkali metal hydrosulfide such as NaHS or an alkali metal sulfide such as Na2S, or gaseous H ₂ S, more preferably comprises or consists of NaHS. Suitable organic sulfides may include thiols, thioamides (e.g., thioacetamide ‘TAA’), thiourea, ... When the source of S ² or HS includes gaseous ¾S, the gaseous source of S ² or HS may be bubbled through the suspension. After passing through the suspension, the gas exiting the suspension and that still contains some source of S ² or HS may be recycled to the suspension.

In some embodiments, less than 100% of the S in the source of S ² or HS is converted to the metal sulfide. Some of the S may be converted to other sulfur- containing species in the modified hydroxyapatite material. Other species of sulfur present in the modified hydroxyapatite material may be in the form of sulfate / sulfite and/or S°.

The contacting with the source of S ² or HS is preferably carried out after the contacting with the metal precursor. There may be a separation between the two contacting steps, but preferably there is no separation between the two contacting steps.

In preferred embodiments in the process for making the modified hydroxyapatite material, when contacting with the source of S ² or HS is carried out after the contacting with the metal precursor, the water from the suspension is preferably not removed from the suspension and the particles contacted with the metal precursor are not washed before the contacting with the source of S ² or HS .

In alternate embodiments although not preferred, the contacting with the source of S ² or HS may be carried out at the same time as the contacting with the metal precursor.

The contacting step with the metal precursor is preferably performed by mixing the suspension containing the hydroxyapatite-containing particles with the metal precursor.

The contacting step with the metal precursor is preferably carried out at a temperature from 10 to 50°C, preferably from 15 to 35°C, more preferably from 18 to 25 °C, most preferably at ambient temperature.

The time period for contacting with the metal precursor is preferably at least 10 minutes, or at least 30 minutes, and/or up to 5 hours, more preferably from 1 hour to 3 hours.

The contacting step with the metal precursor is preferably carried out at a pH from 4 to 10, preferably a pH from 4 to 8.

The contacting step with the source of S ² or HS is preferably performed by mixing the suspension containing the hydroxyapatite-containing particles with the source of S ² or HS .

The contacting step with the source of S ² or HS is preferably carried out at a temperature from 10 to 50°C, preferably from 15 to 35 °C, more preferably from 18 to 25 °C, most preferably at ambient temperature.

The time period for contacting with the source of S ² or HS is preferably at least 10 minutes, or at least 30 minutes, and/or up to 5 hours, more preferably from 1 hour to 3 hours.

The contacting step with the source of S ² or HS is preferably carried out at a pH from 4 to 10, preferably a pH from 4 to 8.

At least a portion of the metal precursor is converted to the metal sulfide during the contacting step with the source of S ² or HS in order for the metal sulfide to be present in the final composition of the modified hydroxyapatite. In some embodiments, during the contacting with the source of S ² or HS , a portion of the metal from the metal precursor is precipitated with S ² or HS to form MeS (see reaction I between Me ²⁺ and HS ) in the modified hydroxyapatite material, while another portion of Me which is not precipitated into MeS may be present in a cationic form, such as Me ²⁺ ’ and/or in the metallic form (Me ⁰ ) in the modified hydroxyapatite material. The metallic form (Me ⁰ ) may be formed via a redox reaction with S ² or HS (e.g., see reaction II with Me ²⁺ and HS ). The reduction would generate solid metallic form (Me ⁰ ) and solid sulfur (S°).

Reaction I : Me ²⁺ + HS MeS + H ⁺

Reaction II : Me ²⁺ + HS Me _soiid + S _soiid + H ⁺

The likelihood of the formation of the metal sulfide in the modified hydroxyapatite material is dictated by the precipitation equilibrium (pKs).

However depending on the redox potential of the metal cation /metal pair (Me _C ation/Me _so iid), there may be a competing side reaction which may direct some of the source of S ² and HS to the formation of Me _so iid and S solid during the contacting step with the source of S ² and HS .

For illustration, TABLE 1 provides the precipitation equilibrium (pKs) of various metal sulfides and TABLE 2 provides the redox potentials of various Me _Cation /Me _soiid pairs compared to the S/H ₂ S and S/HS pairs. For iron, TABLE 2 further includes the redox potential for the pair Fe ³⁺ /Fe ²⁺ .

The formation of solid metallic form (Me ⁰ ) in the modified hydroxyapatite material such as via Reaction II is not desirable because it reduces the metal availability to form the metal sulfide.

In some embodiments, it is preferable to avoid oxidative conditions when the metal precursor and the source of S ² or HS are contacting. In some instances, the suspension may be kept under an inert atmosphere, or an inert gas (such as nitrogen gas N ₂ ) may be bubbled through the suspension in order to minimize oxidative conditions.

When the metal sulfide is deposited on the hydroxyapatite, the metal sulfide is preferably coated at least a portion of the surface of the hydroxyapatite structure in the modified hydroxyapatite material.

TABLE 1 : Precipitation equilibrium (pKs) of various metal sulfides TABLE 2 : Redox potentials

Process for making the hydroxyapatite composite

The second embodiment of the process for making the particulate material includes steps for making a hydroxyapatite composite wherein the at least one metal sulfide is incorporated or embedded into the hydroxyapatite.

The process for producing the hydroxyapatite composite may include forming a hydroxyapatite from separate sources of calcium and phosphate or from a source of calcium and phosphate, and further include the addition of at least one metal sulfide during the hydroxyapatite synthesis.

When the process for producing the hydroxyapatite composite 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“1-step” process.

Therefore when the particulate material comprises a composite wherein the at least one metal sulfide is incorporated or embedded into the hydroxyapatite, a preferred embodiment of the process for producing a hydroxyapatite composite according to the present invention, referred to as a“1-step process”, comprises:

- providing an aqueous suspension (A) comprising particles containing 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 (A) 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 metal sulfide to the suspension (A) before the addition of the alkaline compound or to the suspension (B’) during or after the addition of the alkaline compound, preferably before or during the addition of the alkaline compound, to form the composite.

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

In preferred embodiments, the alkaline compound comprises calcium hydroxide.

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 CaHPCri, 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 preferred embodiments, the step of providing an aqueous suspension may comprise:

- mixing a source of calcium and a source of phosphate ions in water in a molar ratio that is adjusted to obtain a Ca/P molar ratio of between 0.5 and 1.5, preferably between 0.5 and 1.35, 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) comprising particles containing the calcium phosphate compound.

In a preferred embodiment, the process for producing a hydroxyapatite composite according to the present invention, referred to as a“2-step process”, 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 1.5, 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 to form a hydroxyapatite structure; and

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

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

When the metal sulfide 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 metal sulfide 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 metal sulfides may be added. In an example, a first metal sulfide is added in the first step and a second metal sulfide is added in the second step. Alternatively, the first and second metal sulfide may be added in the first step or in the second step.

In some embodiments, the metal sulfide may be in the form of a solution or a slurry before it is added to at least one of the first and second steps of the 2-step process of making the composite or before it is added before or during the alkaline maturation step in the 1-step process of making the composite.

In preferred embodiments, the metal sulfide may be in the form of a solid before it is added to at least one of the first and second steps of the 2-step process of making the composite or before it is added before or during the alkaline maturation step in the 1-step process of making the composite.

In some embodiments, when the D50 particle size of the solid metal sulfide is greater than 100 microns, the process for making the composite may further include grinding or milling the metal sulfide 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 process for making the composite. In some embodiments, when the metal sulfide may be in the form of a powder (either sold‘as is’ or ground before use), the process for making the composite may further include sieving the powder of the metal sulfide 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 metal sulfide which passes through a sieve No. 170 (under ASTM El 1) 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 2-step process of making the composite or before it is added before or during the alkaline maturation step in the l-step process for making the composite.

Moreover the hydroxyapatite composite comprising the metal sulfide according to the invention, when made in the first step in the two-step process at low temperature (less than 40°C, preferably 20-25°C), and the second step in the two-step process 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.

In the 2-step process of the present invention, the source of calcium 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 process 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 process for making the composite 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 2-step process for making the composite of the present invention, phosphoric acid is preferred due to its greater availability and lower cost compared to dihydrogen and monohydrogen phosphate salts.

In the process for making the composite according to the invention, in the first step in the 2-step process, 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 process for making the composite 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 process for making the composite, 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 PO 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 process for making the composite, 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 process for making the composite, 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 2-step process for making the composite 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 CO2 when a source of calcium comprising calcium carbonate is used, before moving on to the second step.

In the 1-step or 2-step process for making the composite according to 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 3, preferably of at most 2, more preferably still of at most 1.8, 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 of the 2-step process for making the composite, 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 1-step process for making the composite, for the alkaline compound used that comprises calcium and hydroxide ions, to include or consist of calcium hydroxide.

In the 2-step process for making the composite according to the invention, it is particularly advantageous 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 a particular preferred embodiment, the process for making the composite takes place in two steps, a first step called "phosphoric 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 CO ₂ in the aqueous phase is reached. Calcium hydrogenphosphate dihydrate

(CaHP0 _4. 2H ₂ 0, also known as brushite) formed in the first step of the 2-step process 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 process has the advantage that it allows the synthesis of hydroxyapatite from relatively inexpensive reagents, compared to other processes, and uses relatively mild conditions of synthesis (temperature and pH).

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 metal sulfide is preferably added out at one time, although the addition of metal sulfide may be carried out in several increments. However, it is to be understood that the addition of the metal sulfide 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 metal sulfide 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 metal sulfide 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 in the 1-step process or formed in the first step in the 2-step process, to the hydroxyapatite structure formed in the (second) alkaline maturation step. For example, the metal sulfide may be added before the addition of the hydroxide ions is initiated in the (second) alkaline maturation step. The metal sulfide may be added even during the first step, particularly if the metal sulfide 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 metal sulfide added in the first step is not degraded/reacted or otherwise rendered ineffective as a metal sulfide for making a hydroxyapatite composite in the (second) alkaline maturation step.

In the process for making the composite according to the 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 in the 2-step process, 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 pm, 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.

It is generally 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 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 metal sulfide 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 metal sulfide may be carried out before or during the addition of hydroxide ions for setting the pH of 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 ¹ ) 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.

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

Process for making the hydroxyapatite mixture with the metal sulfide

When the hydroxyapatite-based particulate materialcomprises a mixture wherein the at least one metal sulfide is physically mixed with the

hydroxyapatite, a third embodiment of the process for making the particulate material comprises:

mixing a hydroxyapatite in the form of particles with at least one metal sulfide.

The mixing is preferably a physical mixing which takes place in dry form such as mixing two solids together.

In preferred embodiments, the metal sulfide is in the form of a solid to make the mixture.

In some embodiments, when the D50 particle size of the solid metal sulfide is greater than 100 microns, the process for making the mixture may further include grinding or milling the metal sulfide 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 mixed with the hydroxyapatite to make the mixture.

In some embodiments, when the metal sulfide may be in the form of a powder (either sold‘as is’ or ground before use), the process for making the mixture may further include sieving the powder of the metal sulfide 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 metal sulfide which passes through a sieve No. 170 (under ASTM El 1) 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 mixed with the hydroxyapatite to make the mixture.

Alternatively and less preferred, the mixing may take place in a dispersing liquid in which a suspension of hydroxyapatite particles is mixed with at least one metal sulfide. Then the suspension may be separated to form wet solids.

The mixing can take place at a temperature, but preferably performed at a temperature not exceeding 50°C, preferably at a temperature of 20-25°C. ADSORBENT OR REACTANT

Another aspect of the present invention relates to an adsorbent or reactant for removal of 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, particularly Hg, from a fluid such as a water or gas effluent, comprising :

- the material in the form of particles according to any embodiment of the invention described herein; or

- two or more materials in the form of particles according to any embodiment of the invention described herein, wherein the metals Me in the metal sulfide in the particulate materials are different, preferably wherein at least one of the metals Me comprises iron, copper or zinc, preferably copper or zinc; or

- a blend of at least one material in the form of particles according to any embodiment of the invention described herein and a hydroxyapatite without metal sulfide in the form of particles.

The adsorbent or reactant may be in the form of a powder or an aqueous suspension.

AQUEOUS SUSPENSION

Another aspect of the present invention also relates to an aqueous suspension comprising the hydroxyapatite-based particulate material comprising a metal sulfide according to the various embodiments of the present invention. The aqueous suspension may comprise at least 0.01wt%, preferably at least 0.03wt% or at least 0.05 wt%, or at least 0.1 wt%, and/or at most 30wt%, preferably at most 20wt%, more preferably at most 10wt%, yet more preferably at most 8 wt%, most preferably at most 6 wt%, of the particulate material in the form of particles according to any embodiment of the invention described herein. The particulate material is preferably obtained by the different processes of making described herein.

In preferred embodiments, the suspension comprises from 0.01 wt% to 10 wt%, preferably from 0.02 wt% to 8 wt or from 0.03 wt% to 6 wt% of the hydroxyapatite-based particulate material.

The hydroxyapatite-based particulate material comprising a metal sulfide may include:

- the modified hydroxyapatite wherein the at least one metal sulfide is

deposited onto the hydroxyapatite, the composite wherein the at least one metal sulfide is incorporated or embedded into the hydroxyapatite, and/or

the mixture wherein the at least one metal sulfide is physically mixed with the hydroxyapatite.

The aqueous suspension may be effective for treating a fluid contaminated by at least one element 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.

In alternate embodiments, the present invention also relates to an aqueous suspension (D) comprising at least 25%, preferably at least 40% and at most 50% of the material particles or to a wet solid (D ¹ ) comprising at least 50% and at most 80% of the material particles, or a pulverulent solid (D") comprising at least 70%, preferably at least 80%, and at most 95% of the material particles and at least 5% and at most 20% of water. The material particles may be according to any embodiment described herein according to the invention. The material particles may be obtained by any embodiment of the processes described herein according to the invention.

USE OF THE HYDROXYAPATITE-BASED PARTICULATE

MATERIAL COMPRISING THE METAL SULFIDE

Another aspect of the present invention also relates to the use of the particulate material or the adsorbent or reactant comprising the particulate material in the form of particles according to any embodiment of the invention described herein, for removing contaminants, e.g., metals, particularly Hg, from a fluid, such as a water or gas effluent.

The present invention also relates to a method for treating a fluid to be treated such as a water or gas effluent or for removing one or more other contaminants from a fluid to be treated, for example contaminants in the form of metals, non-metals, their cations and/or oxyanions, or their respective oxyanions, comprising contacting the hydroxyapatite-based particulate material or the adsorbent comprising at least one hydroxyapatite-based particulate material with the fluid to be treated to remove at least a portion of one or more other contaminants from the fluid.

The present invention also relates to a method for removing Hg from a water or gas effluent, in which the hydroxyapatite-based particulate material or the adsorbent or reactant comprising the hydroxyapatite-based particulate material in the form of particles according to any embodiment of the invention described herein contacts the effluent to remove at least a portion of Hg. In preferred embodiments, the hydroxyapatite-based particulate material is dispersed into a water effluent to form a suspension of from 0.01 wt% to 10 wt%, preferably from 0.02 wt% to 8 wt or from 0.03 wt% to 6 wt%.

The present invention also relates to a process for purifying a substance contaminated by metallic and/or non-metallic contaminants including mercury, according to which the substance is brought into contact with the hydroxyapatite- based particulate material according to any embodiment of the present invention, whether it be in the form of the suspension or a wet solid or a dry solid, in order that at least a portion of the contaminants and in particular Hg, are removed from the substance by the hydroxyapatite-based particulate material.

In the purification or removal process according to the invention, the contaminated substance, fluid, 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-based particulate material or an adsorbent comprising at least one modified hydroxyapatite material, whether it be in the form of the suspension or a wet solid or a dry solid , is dispersed in the flue gases, the flue gases being at a temperature of at least 100°C, or of at least

120°C, or of at least 150°C, and preferably not more than 1100°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 resulting spent solids and a flue gas partially purified of Hg and optionally of other 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 contaminants, such as: Al, Ag, As, B, Ba, Be, Bi, Ce, Co, Cd, Cu, Cr, F, 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, Cr, Cu, Hg, Ni, Pb, and/or Zn, whether these elements may be in the form of cations and/or anions, such as oxyanions, according to which the hydroxyapatite-based particulate material or an adsorbent material or reactant comprising the hydroxyapatite-based particulate material (preferably in suspension form) is mixed into the liquid effluent for a sufficient time such that the hydroxyapatite-based particulate material adsorbs at least a portion of the metallic and/or non-metallic contaminants such as Hg, 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

hydroxyapatite-based particulate material loaded with metallic and/or non- metallic contaminants such as Hg or compounds of Hg, such as with HgS and optionally sulfides of other metallic and/or non-metallic elements that are removed from the liquid effluent. Preferably, the hydroxyapatite-based particulate material 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 hydroxyapatite-based particulate material or the adsorbent / reactant containing it 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 hydroxyapatite-based particulate material or the adsorbent / reactant containing it is present at a concentration of at least 0.01% by weight, preferably at least 0.03 wt%, more preferably at least 0.05 wt% and in general at most 10% by weight, preferably at most 8 wt%, more preferably at most 6 wt%;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 spent

hydroxyapatite-based particulate material or the adsorbent containing them 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 and/or non-metallic contaminants, such as Hg, 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 spent hydroxyapatite-based particulate material 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 the hydroxyapatite-based particulate material 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 these elements upstream (in the liquid effluent) and downstream of the purification unit (in the partially treated liquid), for example by an automatic analyser or by sampling and analysis. The hydroxyapatite-based particulate material charge of the contact reactor is in general regularly renewed in portions. For example, by partial purging of the hydroxyapatite-based particulate material or the adsorbent containing it loaded with metallic and/or non-metallic elements at the underflow from the settling tank, and by adding fresh hydroxyapatite-based material or adsorbent containing it to the contact reactor. Such a process thus ensures a "chemical polishing" of the liquid effluent. The treatment 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 fluid or substance may be a solid residue or a soil contaminated by Hg and other metallic elements such as Al, Ag, As, B, Ba, Be, Bi, Ce, Co, Cd, Cu, Cr, F, Fe, Hf, La, Li, Mg, Mn, Mo, Ni, Pb, Pd, Rb, Sb, Se, Sn, Sr, Th, Ti, U, V, Y, Zn, and/or Zr, preferably Cd, Cr, Cu, Hg, Ni, Pb, and/or Zn„ according to which the hydroxyapatite-based particulate material or the adsorbent / reactant containing it (for example in the form of an aqueous suspension or a wet solid or dried solid of the hydroxyapatite-based particulate material) is injected into the solid residue or the soil in the vicinity of Hg and other metallic and/or non-metallic elements for a sufficient contact time so that the hydroxyapatite-based particulate material removes or adsorbs at least a portion of the Hg and optionally other metallic and/or non-metallic elements.

In particular the present invention relates to the following embodiments: ITEM 1. A particulate material comprising a hydroxyapatite and at least one metal sulfide, which includes:

a mixture wherein the metal sulfide is physically mixed with the hydroxyapatite, a composite wherein the metal sulfide is incorporated or embedded into the hydroxyapatite, and/or

a modified hydroxyapatite wherein the metal sulfide is deposited on the hydroxyapatite.

ITEM 2. The particulate material according to ITEM 1, including a modified hydroxyapatite wherein the at least one metal sulfide is deposited on the hydroxyapatite.

ITEM 3. The particulate material according to ITEM 1, including a composite wherein the at least one metal sulfide is incorporated or embedded into the hydroxyapatite. ITEM 4. The particulate material according to any of ITEMS 1 to 3, wherein the metal in the at least one metal sulfide is selected from the group consisting of iron (Fe), cobalt (Co), manganese (Mn), nickel (Ni), copper (Cu), zinc (Zn), cadmium (Cd), lead (Pb), antimony (Sb), and any combination of two or more thereof, preferably selected from the group consisting of iron (Fe), manganese (Mn), nickel (Ni), copper (Cu), zinc (Zn), antimony (Sb), and any combination of two or more thereof; more preferably selected from the group consisting of iron (Fe), copper (Cu), zinc (Zn) and any combination of two or more thereof; most preferably selected from the group consisting of copper (Cu), zinc (Zn), and any combination thereof.

ITEM 5. The particulate material according to any of ITEMS 1 to 4, wherein the metal sulfide is selected from the group consisting of pyrite (FeS2, cubic), marcasite (FeS2, orthorombic), greigite (Fe3S4, cubic), smythite (FegSn, hexagonal), mackinawite (FeSi_ _x , 0<x<0.07, tetragonal), pyrrhotite (Fei_ _x S, 0<x<0.125, monoclinic and hexagonal), trolite (FeS, hexagonal), CoS, MnS,

NiS, CuS (cupric sulfide), C _¾ S (cuprous sulfide), ZnS, CdS, PbS, Sb2S3, and any combination thereof; preferably selected from the group consisting of pyrite (FeS2, cubic), mackinawite (FeSi_ _x , 0<x<0.07, tetragonal), trolite (FeS, hexagonal), CoS, MnS, NiS, CuS (cupric sulfide), ZnS, CdS, PbS, Sb2S3, and any combination thereof.

ITEM 6. The particulate material according to any of ITEMS 1 to 5, comprising a molar ratio of sulfur to metal (S:Me) of at most 2, preferably at most 1.

wherein the hydroxyapatite is a calcium-deficient hydroxyapatite, preferably a hydroxyapatite with a Ca/P molar ratio more than 1.5 and less than 1.67.

ITEM 7. The particulate material according to any of ITEMS 1 to 6, comprising, based on the total weight of dry matter:

- at least 50wt%, advantageously at least 60wt%, and more advantageously still at least 70wt%, or at least 75wt% of the hydroxyapatite, preferably wherein the hydroxyapatite is a calcium-deficient hydroxyapatite, more preferably a hydroxyapatite with a Ca/P molar ratio more than 1.5 and less than 1.67; and

- from 1 to 20 wt%, preferably from 1 to 15 wt%, more preferably from 1 to 10 wt% of the metal sulfide.

ITEM 8. A process for making the particulate material of any of the ITEMS 2,

4, 5, 6 & 7, said particulate material comprising the modified hydroxyapatite wherein the at least one metal sulfide is deposited on the hydroxyapatite, the process comprising: - making a suspension of hydroxyapatite-containing particles in water;

- contacting the hydroxyapatite-containing particles in the suspension with a precursor of the metal (Me);

- contacting the hydroxyapatite-containing particles in the suspension with a source of S ² or HS , preferably H ₂ S, NaHS or Na ₂ S, more preferably NaHS, to obtain a molar ratio S:Me which is at most 2, preferably at most 1, more preferably at most 0.85, yet more preferably at most 0.7, during or after the contacting step with said metal precursor, preferably after the contacting step with said metal precursor, to deposit the metal sulfide on the hydroxyapatite; - separating the particles from the suspension after contacting with the source of S ² or HS ;

- washing the separated particles with water; and

- recovering the washed particles to form the modified hydroxyapatite

comprising the metal sulfide.

ITEM 9. The process according to ITEM 8, wherein the suspension of the hydroxyapatite-containing particles comprises from 25 to 200 g, preferably from 50 to 150 g, of dry matter per liter of water.

ITEM 10. The process according to ITEM 8 or 9, wherein the precursor of the metal comprises, or consists essentially of, a salt of the metal, preferably an inorganic salt of the metal, more preferably a chloride, nitrate or sulfate salt of the metal, yet more preferably a chloride or nitrate salt of the metal.

ITEM 11. The process according to any of ITEMS 8 to 10, wherein less than 100% of the S in the source of S ² or HS is converted to the metal sulfide.

ITEM 12. The process according to any of ITEMS 9 to 11, wherein the contacting with the source of S ² or HS is carried out after the contacting with the metal precursor, and optionally wherein there is no separation between the two contacting steps.

ITEM 13. The process according to any of ITEMS 6 to 12, wherein the contacting step with the metal precursor and the contacting step with the source are carried about at a pH value from 4 to 10, preferably from 4 to 8.

ITEM 14. A process for making the particulate material according to any of ITEMS 3 to 7, said particulate material comprising the composite wherein the at least one metal sulfide is incorporated or embedded into the hydroxyapatite, the process comprising:

- providing an aqueous suspension (A) comprising particles containing 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 (A) 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 metal sulfide to the suspension (A) before the addition of the alkaline compound or to the suspension (B) during or after the addition of the alkaline compound, preferably before or during the addition of the alkaline compound, to form the composite,

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

ITEM 15. Process according to the preceding ITEM, wherein the alkaline compound comprises calcium hydroxide.

ITEM 16. Process according to ITEM 14 or 15, wherein providing the aqueous suspension (A) comprises:

- mixing a source of calcium and a source of phosphate ions in water in a molar ratio that is adjusted to obtain a Ca/P molar ratio of between 0.5 and 1.5, preferably between 0.5 and 1.35, and reacting the source of calcium with the phosphate ions at a pH of between 2 and 8, in order to obtain the suspension (A) comprising particles containing the calcium phosphate compound.

ITEM 17. An adsorbent material for removal of contaminants, such as Al, Ag, As, B, Ba, Be, Bi, Ce, Co, Cd, Cu, Cr, Fe, Hg, Hf, La, Li, Mg, Mn, Mo, Ni, Pb, Pd, Rb, Sb, Se, Sn, Sr, Th, Ti, U, V, Y, Zn, and/or Zr, preferably Hg, from a fluid, comprising :

- the particulate material according to any of ITEMS 1 to 7; or

- two or more particulate materials according to any of ITEMS 1 to 7, wherein the metal sulfides are different in the two or more particulate materials; or

- a blend of a particulate hydroxyapatite without metal sulfide and at least one particulate material according to any of ITEMS 1 to 7.

ITEM 18. Use of the particulate material according to any of ITEMS 1 to 7 or of the adsorbent material of Claim 17 in the form of particles for removing from a fluid at least a portion of an element selected from the group consisting of Al, Ag, As, B, Ba, Be, Bi, Ce, Co, Cd, Cu, Cr, Fe, Hg, Hf, La, Li, Mg, Mn, Mo, Ni, Pb, Pd, Rb, Sb, Se, Sn, Sr, Th, Ti, U, V, Y, Zn, and/or Zr, preferably for removing Hg from a fluid, such as a water or gas effluent, comprising contacting the particulate material with said fluid for a time sufficient to remove at least 30%, preferably at least 50%, more preferably at least 70% of the element, preferably Hg, from the fluid.

ITEM 19. The process according to any of the ITEMS 8-13, wherein during the contacting with the source of S ² or HS , a portion of Me from the precursor is precipitated with of S ² or HS to form MeS in the modified hydroxyapatite material, while another portion of Me which is not precipitated into MeS is in a cationic form, preferably Me ²⁺ ’ and/or in the metallic form (Me ⁰ ) in the modified hydroxyapatite material, said metallic form (Me ⁰ ) being formed via redox reaction with S ² or HS .

ITEM 20. The particulate material according to any of the ITEMS 1-7 or process according to any of the ITEMS 8-19, wherein a portion of the metal is in the form of said metal sulfide, while another portion of the metal is in a cationic form and/or in the metallic form (Me ⁰ ).

ITEM 21. The particulate material according to any of the ITEMS 1-7 & 20 or process according to any of the ITEMS 8-20, wherein the particulate material has a Me content from 1 to 20 wt%, preferably from 1 to 15 wt%, more preferably from 1 to 10 wt% based on the total dry weight of the particles.

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 pH3110.

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 (P/P0) range varying from around 0.05 to 0.20.

The following commercial chemicals in TABLE 3 were used in the examples that follow. TABLE 3

Example 1 (not in accordance with the invention)

Unmodified hydroxyapatite material 1A. Preparation of unmodified hydroxyapatite materials (without MeS)

In this example, an unmofidied hydroxyapatite material HAP made under similar conditions as those described in example lb of WO2015/173437 patent application. In the first step, limestone was dispersed in water at 20-25°C in a 200-liter reactor (with baffles). Then H ₃ PO ₄ (75%) was added to this suspension and the mixture was stirred 10 hertz using a double 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. 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 in the second step was 260 minutes (4.5 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 20% by weight (solid weight reported to total weight of the aqueous suspension). The aqueous suspension was filtered under pressure on a 0.45 micron paper filter to achieve a wet solid.

The wet solid samples were then dried in an oven at 105°C overnight.

IB. Porosity and particle size after drying of the unmodified hydroxyapatite materials

The porosity characteristics were determined after a heat treatment (drying) at 110 °C under vacuum overnight (about 16 hours). 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 110°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/P0) 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 BET specific surface area and mean particles size D50 for the three samples HAP can be found in TABLE 4.

TABLE 4

1C. Composition of the unmodified hydroxyapatite material after drying

The composition of the unmodified hydroxyapatite material was determined by thermogravimetric analysis (TGA). TGA is a method of thermal analysis in which the weight of a sample is measured over time as the sample is heated at a constant rate, in this case heated from 35 to 250 °C at a rate of 10°C/min. This measurement provides information about the decomposition of the sample. The composition of the material HAP based on TGA analysis can be found in TABLE 5.

TABLE 5

*XRD analysis confirmed that the synthesized material HAP had a hydroxyapatite structure.

Examples 2-8 (in accordance with the invention)

Preparation of modified hydroxyapatite materials with a sulfide of Me= Cd, Co, Ni, Pb, Zn, Cu, or Fe using S:Me=0.65 2A. Preparation of modified hydroxyapatite materials

A mass (50 g of dry equivalent) of the unmodified apatite material HAP (in the form of particles) of Example 1 was mixed in 500 ml of demineralized water in a 2-liter container, followed by adding a mass of a salt precursor of a metal (Me) selected from Cd, Co, Ni, Pb, Zn, Cu, Fe (see TABLE 6 for the metal precursors and their respective mass used). TABLE 6

* MW = molecular weight

The mixture was stirred at 350 rpm at room temperature for 2 hours. Then, 1.25 g of sodium hydrogen hydrate NaHS.H^O (Acros) with a S:Me= 0.65 was added, and stirring (350 rpm) was continued for 2 hours. The mixture was then filtered on a Buchner filter, the solids were washed with deionized water (2 hours, stirred at 10 rpm) and again filtered on a Buchner filter. The washing operation was repeated twice. After final filtration, various wet modified materials HAP -Me S in particle form for Examples 2-8 were recovered.

It was observed during the preparation of the modified materials HAP-MeS ofExamples 2-9 that the pH decreased for all metals except for iron (TABLE 7).

TABLE 7

Example 9 (in accordance with the invention)

Water treatment testing of materials of Examples 1-8 3A. Cationic standard test testing for water treatment on selected metallic cations

3A.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 8 is prepared by adding the salt of each metal in deionized water to reach 1 g M/L content.

TABLE 8

* MW = molecular weight

3 A.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.

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

- Dry approximately 2-3 g of an apatic material 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 mosture meter such as a thermal balance sold by Sartorius.

3 A.4 Steps for the cationic standard test on performance evaluation :

- Take a 100-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 100-ml sample from the suspension after 1 hour and filter it on a 0.45- mhi filter to remove solids;

- Stabilize the two 100-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.

3A.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% HNO3, 1 or 2 mg/1 scandium and, where appropriate, 1 or 2 mg/1 gold.

The determination of contents of specific elements such Cd, Cr, Cu, Mn,

Ni, Pb, Zn, Hg 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/1 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/1, 0.2 mg/1, 0.5 mg/1, 1 mg/1, 2 mg/1 and 5 mg/1 of each element). All the calibration solutions also contain the same concentration of HNO ₃ , scandium and gold as the diluted sample solutions.

3B. Results of the cationic standard test for Examples 1-8

The cationic standard test was carried out with the modified hydroxyapatite materials HAP-MeS of Examples 2-8 and the unmodified material HAP of Example 1. The % removal for the 7 metallic cations and the pH during the standard test are provided in TABLE 9. The pH during the cationic standard test was about the same for all modified hydroxyapatite Examples 2-8, and ranged about 5.4-5.8.

The pH during the cationic standard test was about 4.5 for the unmodified hydroxyapatite Example 1.

For the unmodified hydroxyapatite material HAP of Example 1, the best removal efficiency (>99%) was with Cu and Pb cations, and the least removal efficiency was with Cd, Hg and Ni cations.

For Cd, the removal efficiency compared to 24% with the unmodified hydroxyapatite material HAP (Ex 1 control) was :

- increased with HAP -ZnS, HAP -FeS; and

about the same or slightly decreased with HAP-CoS, FLAP-NiS, HAP- PbS, HAP-CuS.

For HAP-CdS though, there was a release of Cd into the water.

For Cr, the removal efficiency compared to 67% with the unmodified hydroxyapatite material HAP (Ex 1 control) was :

slighty improved with HAP-FeS,

about the same with HAP-CoS, HAP-NiS, HAP -ZnS, and

slighlty decreased with HAP-CdS, HAP-PbS, HAP-CuS.

For Cu, the removal efficiency compared to 99% with the unmodified hydroxyapatite material HAP (Ex 1 control) was :

about the same with HAP-CdS, HAP -ZnS, and

- decreased with HAP-CoS, HAP-NiS, HAP-PbS, HAP-CuS, HAP-FeS.

TABLE 9

(i) leaching of Cd

(ii) leaching of Co

(iii) leaching of Ni

(iv) leaching of Zn

(v) leaching of Fe

For Hg, the removal efficiency compared to 15% with the unmodified hydroxyapatite material HAP (Ex 1 control) was :

- highly improved (90%) with HAP-CdS, HAP-CoS, HAP-PbS, HAP-

ZnS, HAP-CuS;

slighlty improved with HAP-NiS ; and

about the same with HAP-FeS.

For Ni, the removal efficiency compared to 8% with the unmodified hydroxyapatite material HAP (Ex 1 control) was :

about the same with HAP-ZnS, HAP-FeS, and

- decreased with HAP-CdS, HAP-CoS, HAP-NiS, HAP-PbS, HAP-CuS. For Pb removal, the removal efficiency compared to 99% with the unmodified hydroxyapatite material HAP (Ex 1 control) is :

- about the same or slightly decreased (>90%) with HAP-CdS, HAP-

CoS, HAP-ZnS, HAP-CuS, HAP-FeS, and decreased with HAP-PbS and HAP-NiS.

For Zn, the removal efficiency compared to 39% with the unmodified hydroxyapatite material HAP (Ex 1 control) was :

about the same or slightly decreased (>90%) with HAP-CdS, HAP- CoS, HAP-FeS, and

decreased with HAP-NiS, HAP-PbS, HAP-CuS.

For HAP-ZnS with S:Ni=0.65, there was a released of Ni into the water

For most of the modified hydroxyapatite materials, the removal rate for Hg was greatly improved, the modified materials being ranked as follows for Hg: HAP-CdS, HAP-ZnS, HAP-CuS> HAP-CoS, HAP-PbS > HAP-NiS > HAP- FeS.

Comparing the performance of the modified hydroxyapatite materials of Examples 2-8, the best increase in removal efficiency was observed with

Example 6 (HAP-ZnS), which demonstrates an increased removal rate for Cd, Cr, Cu, Hg, Ni. The caveat was that with this material, there was a leaching of Zn as observed by an increase in Zn content in the standard test compared to its initial content of the standard solution.

Examples 10-12 (not in accordance with the invention)

Preparation of sulfides of Ni, Pb, Cu without hydroxyapatite For comparison for Me = Ni, Pb, Cu, the same quantity of metal precursor that was used in Examples 4, 5, 7 was put in contact of the same amount of NaHS (S:Me=0.65 eq.) but in the absence of hydroxyapatite (10 rpm, 1 hour using 0.039 mol Me ² ). See TABLE 10.

TABLE 10

These examples were provide to show that the formation of metal sulfide

(MeS alone) without HAP resulted in a large pH drop (to a value of 1.2 - 1.8) compared to a much moderate pH when the formation of metal sulfide coated on the hydroxyapatite (to a value of 5.4 - 5.8).

Because the pH decrease was much less with HAP -MeS for Examples 4, 5 &7, it seems that the hydroxyapatite in the modified material acted as a buffer during the contacting of the metal precursor and NaHS to form the metal sulfide which is deposited on the hydroxyapatite.

For both NiS and PbS without hydroxyapatite, metallic particles (Me ⁰ ) were observed in the obtained solid materials.

For CuS without hydroxyapatite, there was gaseous release with a pugent odor when the precipitation took place during the contacting of the Cu precursor and NaHS, likely indicating a reaction consuming H and formation of H ₂ S.

Examples 13-15 (in accordance with the invention)

Preparation of modified hydroxyapatite materials with a sulfide of Me= Fe, Mn, or Zn using a molar ratio S:Me= 1

and testing for water treatment

4A. Preparation of modified hydroxyapatite materials

A mass of the unmodified hydroxyapatite material HAP (in the form of particles) of Example 1 was mixed in demineralized water in a container, to obtain a slurry of 10 wt% HAP in water, followed by adding a mass of a salt precursor of a metal (Me) selected from Fe, Mn or Zn. The mixture was stirred at room temperature for 2 hours. Then, a mass of sodium hydrogen hydrate NaHS.H ₂ 0 corresponding to a molar ratio of S:Me=l was added, and stirring was continued for 2 hours (see TABLE 11 for the masses of metal precursors and NaHS .H ₂ 0 used as well of the container size).

TABLE 11

The mixture was then filtered on a Buchner filter, the solids were washed with deionized water (2 hours, stirred at 10 rpm) and again filtered on a Buchner filter. The washing operation was repeated twice. After final filtration, various wet modified hydroxyapatite materials HAP -Me S in particle form for Examples

13-15 were recovered.

4C. Performance testing of modified hydroxyapatite materials of Examples 13-15 The cationic standard test described in Section 3 A under Example 9 was carried out with the modified hydroxyapatite materials HAP-MeS of Examples 13-15. The % removal for the 7 metallic cations and the pH during the cationic standard test obtained with the Examples 13-15, but also with Examples 6 and 8 are provided in TABLE 12 to compare the removal efficiency of the modified hydroxyapatite materials with the same metal sulfide but with differing S:Me molar ratios.

The pH during the cationic standard test was about the same for these two modified hydroxyapatite Examples 13-15, and were 5.6, 5.3 & 4.8, respectively. TABLE 12

(i) leaching of Fe

(ii) leaching of Zn

For Hg, the removal efficiency compared to 15% with the unmodified hydroxyapatite material HAP (Ex 1 control) was :

improved (49%) with Example 13 HAP-FeS using molar S:Fe=l and (22%) with Example 8 HAP-FeS using molar S:Fe=0.65;

about the same (14%) with Example 14 HAP-MnS using molar S:Mn=l ; and

- greatly improved (97%) with Example 15 HAP-ZnS using molar

S:Zn=l and (98%) with Example 6 HAP-ZnS using molar S:Zn=0.65. For the modified hydroxyapatite material with FeS, the Hg removal was improved with Example 13 HAP-FeS using a molar S:Fe=l (49%) compared to that with Example 8 HAP-FeS using the molar S:Fe=0.65 (22%). On the other end, when the molar S:Fe was 0.65 in the modified hydroxyapatite material with FeS, the removal in Cd and Cr was better than when the molar S:Fe was 1.

For the modified hydroxyapatite material with ZnS, the Hg removal (97 & 98%) was about the same with Example 15 HAP -ZnS using a molar S:Zn=l and with Example 6 HAP -ZnS using the molar S: Zn=0.65. But the same trend which was with modified hydroxyapatite material with FeS based on the molar S:Fe and its impact on the removal of the other cationic metals Cd anc Cr was also observed with modified hydroxyapatite material with ZnS. That is to say, when the molar S:Zn was 0.65 in the modified hydroxyapatite material with ZnS, the removal % in Cd and Cr was better than when the molar S:Zn was 1.

This impact of the molar ratio S:Me on the performance of capture for cations other than Hg could be explained as follows: when there was an amount of S for Me equivalent to achieve the stoichiometric ratio of the metal sulfide in the modified hydroxyapatite material HAP-MeS, the Hg removal was enhanced because the presence of S on the hydroxyapatite structure allowed for the capture of Hg to form mercuric sulfide for example. But when the molar ratio S:Me (in this case, S:Me=0.65) was lower than the stoichiometric ratio S:Me to make the metal sulfide, there was an excess of metal compared to S and therefore there was a portion of the metal (Me) not bound to S that was available for capturing cations other than Hg, such as Cd and Cr.

Hence it can be concluded that, in instances when the main metallic contaminant to remove from the effluent is Hg, then a high S:Me approaching the stoichiometric ratio to make the metal sulfide (such as S:Me= 1 or even up to 2) may be preferably used in a modified hydroxyapatite material.

On the other end, in instances when there is a need to remove Hg but also other metallic cations such as containing Cd and Cr, then a S:Me which is lower than the stoichiometric ratio to make the metal sulfide may be preferably used in a modified hydroxyapatite material in order for the bound S in MeS to capture Hg and for the excess or ‘free’ Me to capture other metallic cationic contaminants.

Examples 16-18 (in accordance with the invention)

Preparation of hydroxyapatite mixtures with 3 metal sulfides: CuS,

ZnS, Sb ₂ S ₃ and testing for water treatment 5A. Preparation of hydroxyapatite mixtures

In this example, three hydroxyapatite mixtures with a metal sulfide (MeS):

CuS, ZnS, and Sb ₂ S ₃ labelled“HAP+CuS”,“HAP+ZnS” and“HAP+Sb ₂ S ₃ ” respectively were made by physically mixing the unmodified hydroxyapatite material HAP of Example 1 with a commercial metal sulfide compound (see sources in TABLE 3) in a recipient containing a blade impeller at ambient temperature in order to achieve a content of 7 wt% MeS in the mixture based on the total dry matter weight.

5B. Performance testing of hydroxyapatite mixtures of Examples 16-18

The cationic standard test described in Section 3A under Example 9 was carried out with the mixtures HAP+MeS of Examples 16-18. The % removal for the 7 metallic cations during the cationic standard test is provided in TABLE 13. TABLE 13

For Hg, the removal efficiency compared to 15% with the unmodified hydroxyapatite material HAP (Ex 1 control) was :

- improved (44, 49 & 54%) with all three mixtures HAP+MeS of Examples 16-18 respectively.

For Cd, the removal efficiency compared to 24% with the unmodified hydroxyapatite material HAP (Ex 1 control) was :

- slightly improved (31%) with Example 13 HAP+CuS ; but

- decreased (15 & 13%) with the other two mixtures HAP+MeS of Examples 17 and 18 respectively.

For Cu and Pb, the removal efficiency compared to 99% with the unmodified hydroxyapatite material HAP (Ex 1 control) stayed at 85% or above, but was generally less with all three mixtures HAP+MeS of Examples 16-18.

For Ni, the removal efficiency compared to 8% with the unmodified hydroxyapatite material HAP (Ex 1 control) remained poor and even worse.

Example 19 (in accordance with the invention)

Preparation of hydroxyapatite composite with ZnS and testing for water treatment

6 A. Preparation of a hydroxyapatite composite with ZnS In this example, a hydroxyapatite composite with ZnS labelled“HAP/ZnS” was made with a ZnS compound (ref. 14459) from Aldrich using a two-step process comprising an acid attack step with calcium carbonate and phosphoric acid following by a lime maturation step.

In the first step, limestone was dispersed in water at 20-25°C in baffled 5- liter reactor. Then H3PO4 (75%) was added to this suspension and the mixture was stirred with a rotational speed of 700 ppm 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. The reaction time for the first step was 73 minutes (1 hr 13 min).

At the end of the addition of acid, the second alkaline maturation 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 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 ZnS compound (in the form of a powder) was added to the baffled 5-L reactor after the reaction medium was heated to +/- 50 °C in the second step during the lime addition (after about ¼ of the lime being added) in order to achieve a content of 7 wt% ZnS in the composite based on the total dry matter weight, corresponding to 68.5 g ZnS for 909 g hydroxyapatite.

The reaction time for the second step was 100 minutes (1 hr 40 min). After this 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 the aqueous suspension was about 20% by weight (solid weight reported to total weight of the aqueous suspension).

The suspension was filtered under pressure on a 0.45 micron paper filter before being tested in the cationic standard test. The % dry matter was estimated before carrying this test.

6B. Performance testing of hydroxyapatite composite of Example 19

The cationic standard test according to Section 3 A described under Example 9 was carried out with the ZnS composite of Example 19. The % removal for the 7 metallic cations during the cationic standard test is provided in TABLE 14 for the ZnS composite of Example 19 as well as the modified hydroxyapatite of Example 15 and the hydoxyapatite miture with ZnS of Example 17. Examples 15, 17 and 19 all contained 7 wt% ZnS. TABLE 14

For Hg, the removal efficiency compared to 15% with the unmodified hydroxyapatite material HAP (Ex 1 control) was improved (38%) with the composite HAP+ZnS of Example 19.

With respect to the other cations, the removal efficiency with the composite HAP+ZnS of Example 19 remains the same or was slightly better (for Cd and Ni) compared to that with the unmodified hydroxyapatite material HAP (Ex 1 control).

Examples 20-21 (in accordance with the invention)

Preparation of adsorbents comprising blends of hydroxyapatite and modified hydroxyapatite material with ZnS and

testing for water treatment

7A. Preparation of blends of hydroxyapatite with a modified hydroxyapatite material comprising ZnS

In this example, two adsorbents labelled“HAP+HAP-ZnS” consisting of blends of unmodified hydroxyapatite material HAP with the modified

hydroxyapatite material HAP -ZnS comprising 7 wt% ZnS were made by physically mixing the unmodified hydroxyapatite material HAP of Example 1 with the modified hydroxyapatite material of Example 15 using two different proportions 95: 15 and 80:20 of HAP: HAP -ZnS, for Examples 20 and 21 respectively, in a recipient containing a blade impeller at ambient temperature.

7B. Performance testing of hydroxyapatite mixtures of Examples 16-18

The cationic standard test described in Section 3 A under Example 9 was carried out with the blends HAP +HAP-ZnS of Examples 20-21. The % removal for the 7 metallic cations during the cationic standard test as well as the modified hydroxyapatite of Example 15 (unblended HAP: HAP -ZnS = 0 : 100) and the unmodified hydroxyapatite of Example 1 (HAP: HAP-ZnS = 100 :0) are provided in TABLE 15.

TABLE 15

It was observed as the proportion of the modified hydroxyapatite material was increased in the blend, there was also an increase in the removal in Hg from the water.

Example 22 (in accordance with the invention)

Preparing of a modified hydroxyapatite material with iron sulfide and testing for gas treatment (Hg removal) 8 A. Preparation of the modified hydroxyapatite material with iron sulfide

A mass (73.7g) of a hydroxyapatite material HAP (in the form of particles) was mixed in demineralized water in a container, to obtain a slurry of 10 wt% HAP in water, followed by adding a mass (20. Ig) of iron sulfate . The mixture was stirred at room temperature for 2 hours. Then, a mass of sodium hydrogen hydrate NaHS.H ₂ 0 2,93g corresponding to a molar ratio of S:Fe=0.5 was added, and stirring was continued for 2 hours. The mixture was then filtered on a Buchner filter, the solids were washed with deionized water (2 hours, stirred at 10 rpm) and again filtered on a Buchner filter. The washing operation was repeated twice. After final filtration, the wet modified hydroxyapatite material in particle form for Example 22 was recovered and dried under vacuum during 20 hours et then dried at 100°C during 3 hours. The weight content of the iron sulfide was 7wt%.

8B. Performance testing of Example 22 for Hg removal from gas A gas treatment for Hg removal was carried out using the modified hydroxyapatite material of Example 22.

To carry out the test, a mercury vaporization system was used producing vapors at 20°C containing 0.03 to 0.06 mg/Nm ³ of total mercury from sources of metallic mercury and mercury dichloride. This mercury vaporization system was filled with 170 g of Luminophor powder from Solvay, and 20 g of the HgCk from Signa- Aldrich. The vapors were heated up to 150°C in a tubular furnace to simulate gas emission of an industrial process and were flowed in air at a flowrate of 120 ml/min for up to 60 minutes into a test line containing 170 mg of the modified hydroxyapatite material with iron sulfide of Example 22 or 170 mg of an unmodified hydroxyapatite (similar to the one made in Example 1) as control. At least a portion of the vaporized mercury Hg passing through the hydroxyapatite material was captured, and the remainder of the vaporized mercury not retained on the hydroxyapatite material flowed downstream of the hydroxyapatite material in the test line where a Hydrar® tube (Ref SKC 226-17- 1 A ; 500 mg) was placed. The Hydrar® tube was used for mercury quantification. A mixture of oxides of manganese and copper, also known as hopcalite, contained in the Hydrar® tube trapped the mercury vapor not captured by the hydroxyapatite material. Mercury was then quantified by atomic absorption spectrometer (the so-called "cold vapor"). The assay can be performed in ICP plasma emission spectrometry with cold steam generator or in emission spectrometry conventional ICP plasma but with less sensitivity.

The % removal for Hg during this gas test is provided in TABLE 16.

TABLE 16

For Hg, the removal efficiency compared to 57% with the unmodified hydroxyapatite material HAP (control) was improved (89%) with the modified hydroxyapatite material with iron sulfide of Example 22.

Example 23 (in accordance with the invention)

Large-scale preparation of modified hydroxyapatite material with ZnS and testing for water treatment In this example, a modified hydroxyapatite material with ZnS labelled “HAP-ZnS” was made with a ZnS compound at an industrial scale.

9A. Large-scale production of the modified hydroxyapatite material with zinc sulfide

A suspension containing 21 wt% of a hydroxyapatite material HAP (in the form of particles) was made according to the method in Example 1 in a 200-Liter baffled reactor. This suspension (1093 kg) contained 248 kg of HAP.

A solution containing 20wt% ZnCl ₂ was prepared by mixing 26 kg of ZnC12 in water for a total mass of 130.37 kg.

A solution containing 20wt% NaHS.H ₂ 0 was prepared by mixing 13.88 kg of sodium hydrogen hydrate NaHS.H ₂ 0 in water for a total mass of 69.42 kg.

The solution containing 20wt% ZnCl ₂ was mixed with the HAP suspension at room temperature for 2 hours. Then, the solution of sodium hydrogen hydrate NaHS.H ₂ 0 corresponding to a molar ratio of S:Zn=T was added, and stirring was continued for 2 hours. The modified hydroxyapatite material was left‘as is’ in suspension and its weight content of the zinc sulfide was 7wt%.

9B. Performance testing of the ZnS modified hydroxyapatite material of Example 23

The cationic standard test according to Section 3 A described under Example 9 for water treatment was carried out with the ZnS modified hydroxyapatite material of Example 23, except that the initial concentration for Hg in this test was increased from 1 ppm to 5 ppm and the test was conducted for 1 hour and 20 hours. The % removal for the 7 metallic cations during the cationic standard test is provided in TABLE 17 for the Example 23 that contained 7 wt% ZnS.

TABLE 17

It was observed that the this ZnS modified hydroxyapatite material with S:Zn=l (produced in large-scale operation) performed better in the cationic standard test than the similar ZnS modified hydroxyapatite material (Ex. 15) produced in lab scale.

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.