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Title:
BENEFICIATION OF TITANIUM BEARING MATERIALS
Document Type and Number:
WIPO Patent Application WO/2016/112432
Kind Code:
A1
Abstract:
This invention relates to the beneficiation of titanium bearing materials having a substantial component of anatase and/or rutile and/or pseudorutile structure. Such materials include anatase ores and minerals and other sources of anatase, as well as blends or mixtures that include traditional sources of titanium and titanium dioxide such as ilmenite and titanium slag. The invention is of particular, though not exclusive, interest in the processing of anatase materials to titanium dioxide of pigment quality. The process is additionally effective in processing materials having a substantial component of anatase or rutile, e.g. leucoxene.

Inventors:
BERNARD, Nicholas Glen (Jenkin RoadCapel, Western Australia 6271, 6271, AU)
HUGO, Victor Emmanuel (Jenkin RoadCapel, Western Australia 6271, 6271, AU)
ROWLANDS, Sally-Anne Fiona (48A Kingsall Road, Attadale, Western Australia 6156, 6271, AU)
ROODT, Clasina Maria Susanna (Jenkin RoadCapel, Western Australia 6271, 6271, AU)
Application Number:
AU2016/050012
Publication Date:
July 21, 2016
Filing Date:
January 13, 2016
Export Citation:
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Assignee:
ILUKA RESOURCES LIMITED (Level 23 140 St Georges Terrace, Perth, Western Australia 6000, 6000, AU)
International Classes:
C01G23/053; C22B3/08; C22B3/20; C22B34/12
Domestic Patent References:
WO1992008816A11992-05-29
Foreign References:
EP0475104A11992-03-18
DE2855467A11980-09-18
US20040237719A12004-12-02
US4089675A1978-05-16
Other References:
DATABASE WPI Week 200952, 7 July 2009 Derwent World Patents Index; Class E32, AN 2009-L51362
Attorney, Agent or Firm:
FREEHILLS PATENT ATTORNEYS (Level 43, 101 Collins StreetMelbourne, Victoria 3000, 3000, AU)
Download PDF:
Claims:
CLAIMS

1. A process for beneficiating a titanium bearing material having a substantial component of anatase structure, comprising:

digesting the titanium bearing material in 94 to 98% sulphuric acid or oleum with addition of non-exothermic heat sufficient to raise the temperature to 220°C or above to form a resultant mix;

baking the resultant mix at a baking temperature in the range 220°-300°C, for of at least 4 hours, to form a baked mix; and

dissolving the baked mix with water or dilute acid and separating out a liquor containing predominantly titanium sulphate species.

2. The process of claim 1 , further including the step of hydrolysing the titanium sulphate species to obtain a precipitate of hydrated titanium dioxide.

3. The process of claim 2, wherein the process further includes the step of calcining the precipitated hydrated titanium dioxide to selectively produce either anatase Ti02 or rutile Ti02.

4. The process of any one of claims 1 , 2 or 3, wherein the titanium bearing material is selected from the group consisting of: an anatase ore, an anatase containing ore, an upgraded ore having a higher proportion of anatase than before upgrading, an anatase concentrate, or an anatase containing concentrate.

5. The process of any one of the preceding claims, wherein anatase extraction is at least 90%, expressed as oxides, of the anatase structure in the titanium bearing material.

6. A process for beneficiating a titanium bearing material of having a substantial component of rutile or pseudorutile structure, comprising:

digesting the titanium bearing material in 94 to 98% sulphuric acid or oleum with addition of non-exothermic heat sufficient to raise the temperature to 220°C or above to form a resultant mix;

baking the resultant mix at a baking temperature in the range 220°-300°C, for of at least 4 hours, to form a baked mix; and

dissolving the baked mix with water or dilute acid and separating out a liquor containing predominantly titanium sulphate species.

7. The process of claim 5, further including the step of hydrolysing the titanium sulphate species to obtain a precipitate of hydrated titanium dioxide.

8. The process of claim 7, wherein the process further include the step of calcining the precipitated hydrated titanium dioxide to selectively produce either anatase T1O2 or rutile Ti02.

9. The process of any one of claims 6, 7, or 8, wherein the titanium bearing material is selected from the group consisting of: a rutile or pseudorutile ore, a rutile or pseudorutile containing ore, an upgraded ore having a higher proportion of rutile or pseudorutile than before upgrading, a rutile or pseudorutile concentrate, or a rutile or pseudorutile containing concentrate.

10. The process of any one of claims 6 to 9, wherein rutile or pseudorutile extraction is at least 65%, expressed as oxides, of the rutile or pseudorutile structure in the titanium bearing material

1 1 . The process of any one of the preceding claims wherein the step of digesting the titanium bearing material includes agitating the titanium bearing material with the 94 to 98% sulphuric acid or oleum.

12. The process of claim 1 1 , wherein compressed air or steam is used to agitate the titanium bearing material with the 94 to 98% sulphuric acid or oleum.

13. A process according to any one of the preceding claims, wherein there is substantially no addition of set off water to dilute the 94 to 98% sulphuric acid or oleum. to provide exothermic heat of dilution during the digesting and baking steps.

14. A process according to any one of the preceding claims, wherein said non- exothermic heat is substantially not supplemented by exothermic heat of reaction from dissolution of the sulphuric acid.

15. A process according to any one of the preceding claims, wherein the baking temperature is in the range 220 to 275°C.

16. The process of any one of the preceding claims, wherein the liquor is treated to remove iron prior to the step of hydrolysing the titanium sulphate species.

17. The process of any one of the preceding claims, wherein ferric iron is not present during the step of hydrolysing the titanium sulphate species.

18. The process of any one of the preceding claims, wherein the process further includes the step of upgrading the titanium bearing material prior to the step of digesting the titanium bearing material.

19. The process of any one of the preceding claims, wherein the process is a continuous process.

20. The continuous process of claim 19, wherein at least the step of digesting the titanium bearing material and the step of baking the resultant mixture are carried out in a continuous reactor.

21 . The continuous process of claim 20, wherein the continuous reactor is a screw reactor.

22. The process of any one of the preceding claims wherein the addition of non- exothermic heat includes preheating the titanium bearing material and/or the sulphuric acid with non-exothermic heat to a temperature of 220°C or above prior to the digesting step.

Description:
Beneficiation of titanium bearing materials

Field of the invention

This invention relates to the beneficiation of titanium bearing materials having a substantial component of anatase and/or rutile and/or pseudorutile structure. Such materials include anatase ores and minerals and other sources of anatase, as well as blends or mixtures that include traditional sources of titanium and titanium dioxide such as ilmenite and titanium slag. The invention is of particular, though not exclusive, interest in the processing of anatase materials to titanium dioxide of pigment quality. The process is additionally effective in processing materials having a substantial component of anatase or rutile, e.g. leucoxene.

Background of the invention

One of the two traditional processes for deriving pigment grade titanium dioxide from titanium bearing ores and other materials such as titanium slag is the so-called Sulphate Process devised in the early 20th century. In this process, the ilmenite or titanium slag is digested in concentrated sulphuric acid to produce a cake containing titanium sulphate species and, especially if ilmenite is the feed material, ferrous and ferric sulphates. The cake is dissolved in water or weak acid, and other solids are separated to derive a liquor, known as a "black liquor", containing titanium sulphate species, particularly titanyl sulphate TiOS0 4 . In the case of an ilmenite feed material, scrap iron is employed to reduce the ferric iron, and the iron is subsequently crystallised out as ferrous sulphate, known as copperas, by reducing the solution temperature.

The titanium sulphate species are hydrolysed by heating the solution, usually above 80°C, to obtain a precipitate of hydrated titanium dioxide. The earlier reduction of ferric iron was necessary as ferric sulphate has a tendency to co-precipitate with the titanium. The wet pulp product of the hydrolysis step is then calcined in an internally fired, inclined rotary kiln in which the pulp is dried and strongly adsorbed water, SO2 and SO3 are driven off and the amorphous TiO(OH) 2 is converted to anatase or rutile pigments according to the applied conditions. For example, seeding is employed in the hydrolysis step to obtain a downstream rutile product, otherwise anatase will result.

The current process for digestion stage involves:

Grinding the ore to provide surface area for the reactions. Mixing the ground ore with the required amount of 98% sulphuric acid in excess to the stoichiometric requirements typically by about 10% for the formation of sulphate species from the metallic elements present (ie Ti, Fe, Mn, V, Al, Mg, Ca etc.). Mixing in the plant is usually carried out with compressed air and/or steam. The typical acid to titania (A:T) ratio for ilmenite is 1 .7-2.0 and for slag 1.6-1.75.

Addition of water (known as set off) to dilute the acid from 98% to between 85 and 95% (the acid attack strength), depending on the mineral being used, to cause an increase in heat of mixture through the heat of solution generally to around 80-130°C. This is often supplemented with direct steam addition. The lower temperature is used for high Fe feeds such as ilmenite as the FeO dissolution reaction is highly exothermic while the T1O2 dissolution reaction is weakly exothermic. The lower FeO slag requires a higher starting temperature (of about 130°C) to achieve the overall >200°C reaction temperature by exothermic reaction.

The reaction then proceeds exothermically such that the temperature rises to 200-220°C, depending on the ore being reacted, generally forming a cake which can have a consistency from treacle through to solid. Compressed air and/or steam mixing continues during this stage.

Once the temperature peaks, the reaction mixture is left to "bake" for ~45 minutes for ilmenite and 5-6 hours for slag. The heat loss at the industrial scale is minimal as the reactors are refractory lined and the external surface area of the reactor compared to the volume of the reactants is low. Thus the peak temperature of 200-220°C is largely retained during the baking stage.

After baking is complete, the cake is dissolved with water or dilute (usually recycled) sulphuric acid. The Ti and other sulphates are thereby included in the solution phase. The amount of acid that is recycled is controlled to ensure that the acid to titanium ratio (A:T) is kept 1 .75-1.85 (where the ratio is H2SO4 to Ti0 2 where all the T1OSO4 is converted to T1O2 and H 2 S0 4 ) as higher acid ratios adversely affect the hydrolysis stage.

The remaining residue is usually filtered and washed to collect any remaining liquor and then disposed of. The residue contains insoluble mineral phases (e.g. silica and alumino-silicates) and any insoluble Ti phases such as rutile and pseudorutile, insoluble forms of Fe such as magnetite and insoluble sulphate species which can include sulphates of Ba, Sr, Ca and the insoluble a-TiOS0 4 .

It has been generally found that the conventional Sulphate Process cannot be successfully and commercially applied to anatase ores and anatase-containing ores, primarily because the anatase is insufficiently soluble under the conditions of the conventional sulphuric acid digestion step. It is also generally thought that rutile and pseudorutile are substantially insoluble in concentrated sulphuric acid and so cannot be treated by the Sulphate Process.

International patent publication WO 92/08816 and Brazilian patent application PI 9005841 A disclose a Sulphate-like process in which an upgraded concentrate from certain anatase ores can be successfully treated to produce titanium dioxide of pigment grade. According to the disclosure of WO 92/08816, the upgraded anatase concentrate is digested in sulphuric acid and conditions are controlled so that, after the digestion is completed, a crystallised cake of titanium sulphates is produced. This cake is dissolved with water or recycled liquor to obtain a 'black liquor' containing predominantly titanium sulphate species, which is treated by the usual further steps of the Sulphate Process to obtain pigment grade titanium dioxide.

The digestion stage in the process of WO 92/08816 differs from the conventional Sulphate Process in that a mixture of concentrated sulphuric acid, ore and crystallized titanium sulphates, similar to a fine sand, is maintained in suspension, and in a fluid phase, with a large excess of acid, i.e. A:0 from 2: 1 to 10: 1. The suspension is maintained under boiling conditions in an equilibrium that causes the titanium sulphates to crystallise.

The liquor resulting from this process cannot be used in the standard sulphate process "back end" as the acid to titanium (A:T) ratio is too high, which makes hydrolysis ineffective. Also, the use of a large excess of acid is uneconomic due to the higher cost of the excess acid and the need to neutralise (with lime) and dispose of the excess acid. Thus the process would require a redesigned, (and new) plant to generate the final Ti0 2 pigment from the leach solutions.

European patent publication EP 0475104 discloses a process for working up the digestion residue that remains after titanium dioxide has been produced via the Sulphate Process. The digestion residue is effectively the solids that remain after the step of removing the soluble sulphate species generated by the Sulphate Process.

EP 0475104 discloses that the digestion residue can contain from 20 to 60% Ti (as ΤΊΟ 2 ). The Ti is present in insoluble phases, including: rutile, pseudorutile, ilmenomagnetite, leucoxene and insoluble a-TiOS0 4 . The digestion residue is also known to typically contain high proportions of Ca, Mg, Mn, Al, Si, and Fe oxides (such as magnetite), and Ba and Sr sulphates. EP 0475104 further discloses that the Ti0 2 in this digestion residue cannot be extracted under the usual conditions of the Sulphate Process, and is therefore typically rejected or recycled into a pulping process for further extraction albeit at low yield. EP 0475104 proposes a process for recovering Ti0 2 from this digestion residue.

EP 0475104 describes a two-stage process for enhanced recovery of Ti0 2 , including a first stage of treating an ore using the conventional Sulphate Process, and a second stage of extracting further Ti0 2 from the resultant digestion residue. In this second stage, EP 0475104 discloses mixing the digestion residue with sulphuric acid in a Ti0 2 :H 2 S0 4 ratio of from 1 :1 to 1 :3.5 and then supplying heat energy to heat this mixture to a temperature of 120°C to 300°C for a period of 15 minutes to 20 hours. EP 0475104 discloses that the energy is supplied by addition of water to the mixture. The dilution of sulphuric acid in water is an exothermic process which generates sufficient exothermic heat to raise the temperature of the mixture to within the aforementioned range of 120°C to 300°C. After the digestion step, EP 0475104 discloses that Ti0 2 can be recovered according to the usual conditions of the Sulphate Process.

It is an object of the invention to provide a practical application of the Sulphate Process to the processing of titanium bearing ores and other materials having a substantial component of anatase and/or rutile and/or pseudorutile structure, to produce pigment grade rutile or anatase.

Reference to any prior art in the specification is not an acknowledgment or suggestion that this prior art forms part of the common general knowledge in any jurisdiction or that this prior art could reasonably be expected to be understood, regarded as relevant, and/or combined with other pieces of prior art by a skilled person in the art.

Summary of the invention

In a first aspect of the invention there is provided a process for beneficiating a titanium bearing material having a substantial component of anatase structure, comprising: digesting the titanium bearing material in 94 to 98% sulphuric acid or oleum with addition of non-exothermic heat sufficient to raise the temperature to 220°C or above to form a resultant mix;

baking the resultant mix at a baking temperature in the range 220°-300°C, for of at least 4 hours, to form a baked mix; and

dissolving the baked mix with water or dilute acid and separating out a liquor containing predominantly titanium sulphate species.

In an embodiment, the process further includes the step of hydrolysing the titanium sulphate species to obtain a precipitate of hydrated titanium dioxide.

In an embodiment, the titanium bearing material is selected from the group consisting of: an anatase ore, an anatase containing ore, an upgraded ore having a higher proportion of anatase than before upgrading, an anatase concentrate, or an anatase containing concentrate.

In an embodiment, anatase extraction is at least 90%, expressed as oxides, of the anatase structure in the titanium bearing material. That is, at least 90% of the anatase structure in the titanium bearing material is separated out in the liquor.

In a second aspect of the invention, there is provided a process for beneficiating a titanium bearing material of having a substantial component of rutile or pseudorutile structure, comprising:

digesting the titanium bearing material in 94 to 98% sulphuric acid or oleum with addition of non-exothermic heat sufficient to raise the temperature to 220°C or above to form a resultant mix;

baking the resultant mix at a baking temperature in the range 220°-300°C, for of at least 4 hours, to form a baked mix; and

dissolving the baked mix with water or dilute acid and separating out a liquor containing predominantly titanium sulphate species.

In an embodiment, the process further includes the step of hydrolysing the titanium sulphate species to obtain a precipitate of hydrated titanium dioxide.

In an embodiment, the titanium bearing material is selected from the group consisting of: a rutile or pseudorutile ore, a rutile or pseudorutile containing ore, an upgraded ore having a higher proportion of rutile or pseudorutile than before upgrading, a rutile or pseudorutile concentrate, or a rutile of pseudorutile containing concentrate.

In an embodiment, rutile or pseudorutile extraction is at least 65%, expressed as oxides, of the rutile or pseudorutile structure in the titanium bearing material. That is, at least 65% of the rutile or pseudorutile structure in the titanium bearing material is separated out in the liquor.

The inventors have found that use of non-exothermic heat energy provides many advantages over the use of exothermic heat energy as per the traditional Sulphate Process. The term non-exothermic heat refers to heat that is added to the system from an outside source and not generated from a reaction between constituents within the system. Such heat may be supplied by a heating element, heat exchanger, or direct contact between the titanium bearing material and/or 94 to 98% sulphuric acid or oleum with a heated or superheated gas (including steam). The use of a superheated gas is advantageous as it also assists to agitate the mix of the titanium bearing material and the sulphuric acid.

As discussed previously in the background section, in a standard process for digestion of ilmenite, sulphuric acid is mixed with the ilmenite and then diluted. The dilution of sulphuric acid is a highly exothermic reaction which generates sufficient exothermic heat to drive the digestion and baking steps of the Sulphate Process. Obtaining heat energy from this exothermic dissolution reaction is generally considered advantageous in the context of the Sulphate Process as it reduces energy costs, i.e. externally applied heat is not required.

While this process is useful for ultimately extracting T1O2 from ilmenite, the process is ineffective for removing T1O2 from a titanium bearing material having a substantial component of anatase, rutile, or pseudorutile.

The inventors have found that providing non-exothermic heat for the digestion and baking steps of the inventive process has a number of advantages in respect of a titanium bearing material having a substantial component of anatase, rutile, or pseudorutile. In particular, the titanium bearing material and sulphuric acid or oleum can be heated to temperatures higher than that generally adopted in the Sulphate Process (for example 220°C or above) and the sulphuric acid or oleum can be maintained at high concentration. The inventors believe that this allows for efficient recovery of T1O2 from a titanium bearing material having a substantial component of anatase, rutile, or pseudorutile.

In an embodiment of the first and second aspects, the step of digesting the titanium bearing material includes agitating the material with the 94 to 98% sulphuric acid or oleum. Preferably, compressed air and/or steam (e.g. superheated steam) is used to agitate the titanium bearing material with the 94 to 98% sulphuric acid or oleum.

While some residual moisture may be present on the titanium bearing material (whether from upstream processing, or due to steam condensation from agitation), this moisture is present in such small quantity that it is insufficient to substantially dilute the 94 to 98% sulphuric acid or oleum, and thus any exothermic heat that is generated will be insufficient to increase the temperature of the mix to 220°C or above for digestion and baking in the absence of the non-exothermic heat.

In an embodiment of the first and second aspects, there is substantially no addition of set off water to dilute the 94 to 98% sulphuric acid or oleum to provide exothermic heat of dilution during the digesting and baking steps. Preferably there is no addition of set off water.

As above, due to the presence of residual moisture some exothermic heat may be generated. However, the heat is predominantly added as non-exothermic heat. Thus, the heat energy added to raise the temperature from a base temperature (such as from ambient) to 220°C or above is predominantly non-exothermic heat. In such cases, the non-exothermic heat accounts for more than 50% of the total energy required to raise the temperature to 220°C or above, preferably 60%, more preferably 70%, even more preferably 90%, and most preferably 95%. However, in a preferred embodiment of the first and second aspects, said non-exothermic heat is substantially not supplemented by exothermic heat of reaction from dissolution of the sulphuric acid or oleum.

It will be appreciated that this non-exothermic heat may be provided by different mechanisms. In an embodiment, the titanium bearing material and optionally also the sulphuric acid or oleum are preheated with non-exothermic heat e.g. to a temperature of 220°C or above prior to the digesting step. In another embodiment, the non-exothermic heat is added with the sulphuric acid feed. In this case, the sulphuric acid or oleum feed is preheated so that during the digestion step, the temperature is raised to 220°C or above. In an embodiment of the first and second aspects, the baking temperature is in the range 220 to 275°C.

In an embodiment of the first and second aspects, the liquor is treated to remove iron prior to the step of hydrolysing the titanium sulphate species.

In an embodiment of the first and second aspects, ferric iron is not present during the step of hydrolysing the titanium sulphate species.

In an embodiment of the first and second aspects, the process further includes the step of upgrading the titanium bearing material to separate the titanium bearing material from gangue prior to the step of digesting the titanium bearing material.

In an embodiment of the first and second aspects, the process is a continuous process.

Preferably, the continuous process is further defined in that at least the step of digesting the titanium bearing material and the step of baking the resultant mixture are carried out in a continuous reactor.

Preferably, the continuous process is further defined in that the continuous reactor is a screw reactor.

In an embodiment of the first or second aspects, the process further includes the step of calcining the precipitated hydrated titanium dioxide to produce anatase ΤΊΟ 2 .

In an alternative embodiment of the first or second aspects, the process further includes the step of calcining the precipitated hydrated titanium dioxide to produce rutile ΤΊΟ 2 .

Brief description of the drawings

Figure 1 is a process flow diagram illustrating an embodiment in which the process of the invention is carried out in a mixed tank reactor.

Figure 2 is a process flow diagram illustrating an embodiment in which the process of the invention is carried out in a screw reactor.

Figure 3 is a process flow diagram illustrating an embodiment in which the process of the invention is carried out using a mixing tank and a screw reactor.

Detailed description

In accordance with the invention, it has been found that anatase ores and other anatase-containing and rutile or pseudorutile-containing titanium bearing materials can be successfully treated by the Sulphate Process with certain modifications of the conventional digestion and baking steps. In particular, the conventional digestion step is modified by providing sufficient non-exothermic heat to reach reaction temperatures of 220°C or above for baking. It has also been found that the higher the bake temperature, the shorter the bake time required, getting as low as 4 hours (which is not dissimilar to the existing process 5-6 hours for slag). It has further been found that the longer the time for the subsequent dissolution stage, the higher the yield of the ΤΊΟ2 to the TiOS0 4 solution.

The invention accordingly provides, in the first aspect, a process for beneficiating a titanium bearing material having a substantial component of anatase structure, comprising:

digesting the titanium bearing material in 94 to 98% sulphuric acid or oleum with addition of non-exothermic heat sufficient to raise the temperature to 220°C or above, baking the resultant mix at a baking temperature in the range 220°-300°C, for of at least 4 hours;

dissolving the baked mix with water or dilute acid and separating out a liquor containing predominantly titanium sulphate species; and

thereafter hydrolysing the titanium sulphate species to obtain a precipitate of hydrated titanium dioxide.

In the second aspect, the invention provides a process for beneficiating a titanium bearing material having a substantial component of rutile or pseudorutile structure, comprising:

digesting the material in 94 to 98% sulphuric acid or oleum with addition of non- exothermic heat sufficient to raise the temperature to 220°C or above,

baking the resultant mix at a baking temperature in the range 220°-300°C, for of at least 4 hours,

dissolving the baked mix with water or dilute acid and separating out a liquor containing predominantly titanium sulphate species; and

thereafter hydrolysing the titanium sulphate species to obtain a precipitate of hydrated titanium dioxide. The invention is especially useful when applied to alteration products of ilmenite containing mixtures of two or more of anatase, rutile and pseudorutile. A typical such product is the mineral mixture leucoxene.

In some applications, e.g. minerals deficient in iron, where there is no exothermic heat potentially available for the digestion and baking steps, all of the required heat may be provided externally, i.e. non-exothermically. In other cases, e.g. certain blended mineral products, there may be some exothermic heat of reaction available during digestion and baking.

Typically, there is no addition of water, i.e. set off to dilute the acid and thereby add exothermic heat. It will be appreciated that there may be some amount of water associated with the titanium bearing material, particularly where the titanium bearing material has been subjected to some form of pre-treatment or upgrading. For example, where the titanium bearing material has a substantial component of anatase structure, it is likely that this material will be provided in the form of a filter cake. This filter cake will likely include residual moisture. However, this residual moisture is present in such small quantity that it is insufficient to substantially dilute the 94 to 98% sulphuric acid, and thus any exothermic heat that is generated will be insufficient to increase the temperature of the mix to 220°C or above for digestion and baking in the absence of the non-exothermic heat.

The first aspect of the invention is especially applicable to a variety of titanium bearing materials of predominately anatase structure. Without limitation, these include anatase in occurrences as a primary mineral and as an alteration product of other titanium bearing minerals such as ilmenite, sphene, perovskite and potentially titaniferous magnetite. These occurrences can be associated with: weathering of alkaline intrusive complexes, hydrothermal alteration or sedimentary (placer) deposits, sedimentary metamorphic deposits and bauxite or laterite hosted minerals.

Preferably, the baking temperature is in the range 220 to 275°C, more preferably at least 230°C and most preferably at least 240°C, more preferably at most 260°C, most preferably at most 250°C. Generally, the non-exothermic heat provided during the digestion step is sufficient to maintain the baking temperature within the desired range for the duration of the bake. However, it will be appreciated that in some instances it may be desirable to provide further non-exothermic heat to maintain the desired baking temperature. Typically, the baking step converts the mix to a sulphate cake, i.e. a solid mix of sulphates.

The proportion of sulphuric acid provided is typically sufficient for the stoichiometric requirements of the acid-consuming reaction(s) plus an excess, typically about 10%. The duration of the baking is preferably in the range 2 to 18 hours, more preferably in the range 4 to 12 hours.

The bake is preferably such, for example in relation to A:0 ratio, temperature and duration, that the anatase extraction is at least 90%, more preferably at least 95% (expressed as oxides).

The bake is preferably such, for example in relation to A:0 ratio, temperature and duration, that the rutile or pseudorutile extraction is at least 65%, more preferably at least 80%, most preferably at least 90% (expressed as oxides).

Rutile extraction can reach a value greater than 80% more preferably at least 85%, most preferably at least 90% (expressed as oxides), but can be tailored according to the desired liquor properties and baking conditions.

The titanium bearing material feed for the process may typically be an anatase, or an anatase containing ore such as a leucoxene ore and/or may often be a prepared concentrate. The anatase or anatase containing ore may be treated in a number of different ways prior to the digestion step depending on the form and morphology. Some occurrences, such as those typified by the anatase present in the Murray Basin of Australia, will require some upgrading. Such upgrading may be by conventional mineral sands concentration processes. Weathered alkaline complexes will require some upgrading using conventional techniques such as light crushing, wet magnetic separation, attritioning and desliming, while others such as hydrothermally altered rock deposits would require crushing and grinding and perhaps concentration techniques such as flotation to liberate the anatase from the silica host matrix, or at least to make the anatase accessible to the acid attack in the digestion step.

In the digestion step, the mixture of feed titanium bearing material in sulphuric acid is preferably agitated, e.g. preferably by means of compressed air, steam (typically superheated) or by physical means, such as through the use of an agitator.

Any iron present prior to the hydrolysis of the liquor may be removed if necessary by crystallisation as hydrated ferrous sulphate (copperas). In general, ferric iron is preferably not present for the hydrolysis step as this has a tendency to co-precipitate with the titanium and would be reduced to the ferrous form prior to crystallisation.

The hydrolysis step may be effected by increasing the temperature of the titanium sulphate solution to cause the precipitation of hydrated titanium dioxide, for example to ~80°C. Precipitation of hydrated titanium dioxide may be accelerated by introduction of nuclei, in either anatase or rutile form. In general, the hydrolysis step may be substantially according to the conventional Sulphate Process.

Typically, the precipitated hydrated titanium dioxide once calcined is in the anatase form, but the calcination (see below) may produce either anatase or rutile pigment according to the conditions and according to the nature of the nuclei added in the hydrolysis stage.

Preferably, the precipitated hydrated titanium dioxide is calcined, e.g. in internally fired inclined rotary kilns through which the titanium dioxide pulp travels by gravity. The precipitate may be treated prior to calcination, for example by being filtered and washed and/or being leached under reducing conditions to eliminate any residual ferric iron. The calcination may be substantially according to the conventional Sulphate Process. In the kiln, the hydrated titanium dioxide is initially dried before strongly adsorbed water, SO2 and SO3 are driven off. Conditions in the kiln are controlled to manage crystallite growth, so as to form either anatase or rutile pigment as desired. The temperature is typically in the region of 1000°C.

Prior to the hydrolysis step, the process may, as required, include treating the liquor to selectively separate one or more impurities from the titanium sulphate species. The selective separation may where appropriate be by solvent extraction and/or ion exchange.

The impurities separated in the selective separation treatment of the liquor containing predominantly titanium sulphate species may typically include at least one or more transition metals, e.g. chromium, vanadium and niobium, and/or the elements derived from the rare earth minerals monazite, xenotime, or crandalite in the original ore.

In an embodiment, the selective separation may be of the transition metals. These are expected to be present as soluble sulphates. A suitable solvent extraction system for this purpose would be triazoloquinazolinone or the neutral organophosphorous tri-n- octylphosphine oxide (TOPO). In another embodiment, the selective separation is effected by extracting the titanium sulphate species from the liquor, which retains the impurities. Reagents such as the organophosphoric acid di(2octylhexyl)phosphoric acid (D2EHPA) or the neutral organophosphorous tri-n-octylphosphine oxide (TOPO) are known to extract T1OSO4 from acidic (sulphate and chloride) solutions. TOPO will extract a range of transition metals so may not be selective enough for preventing the transition element oxides co- extracting but it is known that Cr(lll) does not extract from acidic solution of TOPO. After extraction, the titanium sulphate species are stripped for subsequent hydrolysis from the extracting reagent by contacting the pregnant organic solution with a dilute sulphuric acid phase.

Typically, the step of treating the liquor to selectively separate one or more impurities from the titanium sulphate species would involve a number of stages designed to treat the different impurities or elements separately since in most cases a single extraction system would not cover all of the required elements.

It will be appreciated that the process may be a batch process, such as one conducted in one or more batch reactors; a semi-continuous process; or a continuous process, such as one conducted in one or more continuous stirred tank type reactors, and/or one or more plug flow type reactors. Alternatively, some parts of the process may be batch operations, while others are continuous. However, it is preferred that the process is a continuous process.

A preferred type of continuous reactor is a screw reactor. Screw reactors include a helical rotating blade or two intermeshing blades that drive the mixture along the reaction volume of the reactor. The blade assists with mixing, and advantageously maintains the mixture in a granular form, which granules are typically 20 to 50 mm in diameter.

Figure 1 is a process flow diagram of a batch process 100. Titanium bearing material, e.g. an anatase ore or concentrate, or an anatase containing ore or concentrate, is fed into a reactor 102 via first inlet 104. 94 to 98% sulphuric acid or oleum is fed into the reactor 102 via a second inlet 106. In this case, a stirrer 108 is used to mix the titanium bearing material and the sulphuric acid or oleum. However, it will be appreciated that different stirring or mixing systems can be used. Once the mixture has been formed it undergoes digestion and baking within the reactor 102. As previously mentioned, during the digestion step, the mixture of feed titanium bearing material in sulphuric acid is preferably agitated by means of compressed air or steam (not shown). After digestion and baking, the baked mix is withdrawn from the reactor 102 via outlet 110 and thereafter subjected to downstream processing, including hydrolysing the titanium sulphate species to obtain a precipitate of hydrated titanium dioxide.

The titanium bearing material and the sulphuric acid or oleum may be heated prior to being fed into the reactor 102, or may be heated within the reactor 102.

In this embodiment, non-exothermic heat is provided to raise the temperature of the titanium bearing material feed and the sulphuric acid or oleum feed so that on mixing the temperature of the resultant mix is 220°C or above. Preferably, the heating step raises the temperature of each of the titanium bearing material feed and the sulphuric acid or oleum feed to 220°C or above. The non-exothermic heat is generally provided by a heat exchanger or heating element (see heating elements 1 12 and 1 14 on feed streams 104 and 106). In an alternative embodiment, non-exothermic heat is provided to raise the temperature of the mix in the reactor 102. In this case, the reactor 102 includes a heat exchanger or heating element.

Figure 2 is a process flow diagram of a continuous process 200. Titanium bearing material, e.g. an anatase ore or concentrate, or an anatase containing ore or concentrate, is fed into a continuous reactor 202 via first inlet 204. 94 to 98% sulphuric acid or oleum is fed into the reactor 202 via a second inlet 206. In this case, the continuous reactor 202 is a screw reactor, having a central threaded bore 208 for mixing the titanium bearing material and the sulphuric acid or oleum and transporting that mixture from the inlets 204 and 206 within the reactor to the outlet 210. In this case, the reactor includes a first zone 212 and a second zone 214. Mixing of the titanium bearing material and the sulphuric acid or oleum occurs in the first zone 212, with digestion and baking of the resultant mixture occurring within the second zone 214. After digestion and baking, the baked mix is withdrawn from the reactor 202 via outlet 210 and thereafter subjected to downstream processing, including hydrolysing the titanium sulphate species to obtain a precipitate of hydrated titanium dioxide.

It will be appreciated that instead of using a single continuous reactor having a first mixing zone and a second digestion and baking zone, two separate continuous reactors in series could instead be used.

As with the embodiment of Figure 1 , the titanium bearing material and the sulphuric acid or oleum may be heated using non-exothermic heat prior to being fed into the reactor 202, or within the reactor 202. In this embodiment, the reactor 202 includes a heating element 216 in the first zone to heat the mix to the desired temperature prior to the digestion and baking stages. In alternative embodiments, the feed may be pre-heated prior to introduction into reactor 202 or may be heated in the second zone 214 of the reactor 202.

Figure 3 is a process flow diagram of another process 300. In this case, two separate reactors are used. The first reactor 302 is a mixing vessel that receives titanium bearing material via a first inlet 304 and 94 to 98% sulphuric acid or oleum via a second inlet 306. This reactor 302 may be operated as a batch reactor or a continuous stirred tank reactor. After mixing, the resultant mix exits reactor 302 and is fed into screw reactor 308 via line 310 for digestion and baking. After digestion and baking, the baked mix is withdrawn from the reactor 308 via outlet 312 and thereafter subjected to downstream processing, including hydrolysing the titanium sulphate species to obtain a precipitate of hydrated titanium dioxide.

As above, non-exothermic heat may be provided at various stages of the process to provide a titanium bearing material/sulphuric acid or oleum mixture with a temperature of 220°C or above. For example, the individual feeds to vessel 302 may be preheated; or heating of the resultant mixture may take place in vessel 302, line 310, or a first zone of vessel 308. In this embodiment, reactor 302 includes a heating element 314 to heat the titanium bearing material and the sulphuric acid or oleum as it is mixed to the desired temperature prior to being fed into reactor 308 for the digestion and baking stages.

In all of the above described processes, it will be appreciated that the feed of titanium bearing material into the reactors may contain residual moisture due to upstream processing. For example, in some instances the titanium bearing material stream will have been subjected to an upstream beneficiation processes, such as flotation, filtration, solid-liquid extraction, etc. In these cases, the titanium bearing material may include some entrained moisture. However, when combined with sulphuric acid, the quantity of entrained moisture is insufficient to substantially dilute the sulphuric acid and thus unable to generate exothermic heat to raise the temperature of the mix to 220°C or above.

EXAMPLES

Example 1 A rutile and anatase concentrate was milled and mixed with concentrated sulphuric acid at a mass ratio of 1.5 acid to 1 ore. The resulting mixture was baked at 250°C for eight (8) hours to produce a sulphate cake. The cake was dissolved with 10% sulphuric acid to produce a solution of titanyl sulphate. This resulted in a total extraction of 98% of anatase, 92% of rutile and 92.0% of total Ti0 2 . The feed and dissolution residue assays are provided in table 1 .

Table 1 : Feed and residue assays for Example 1

Example 2

A rutile and anatase concentrate was milled and mixed with concentrated sulphuric acid at a mass ratio of 1.5 acid to 1 ore. The resulting mixture was baked at 250°C for four (4) hours to produce a sulphate cake. The cake was dissolved with 10% sulphuric acid to produce a solution of titanyl sulphate. This resulted in a total extraction of 98% of anatase, 84% of rutile and 86.7% of total Ti0 2 . The feed and dissolution residue assays are provided in table 2.

Relative to example 1 , the substantial reduction in duration of the bake has not significantly affected the anatase recovery but rutile recovery is somewhat less. Table 2: Feed and residue assays for Example 2

Example 3

A rutile and anatase concentrate was milled and mixed with concentrated sulphuric acid at a mass ratio of 1.2 acid to 1 ore. The resulting mixture was baked at 220°C for twelve (12) hours to produce a sulphate cake. The cake was dissolved in water to produce a solution of titanyl sulphate. This resulted in a total extraction of 98% of anatase, 85% of rutile and 84.4% of total Ti0 2 . The feed and dissolution residue assays are provided in table 3.

Relative to example 1 , the reduction in acid and temperature but increase in duration has dissolved rutile recovery similarly to example 2 but not substantially affected anatase recovery.

Table 3: Feed and residue assays for Example 3 Anatase (%) 36 3 98

Rutile (%) 33 16 85

Ti0 2 (%) 76.2 37.7 84.4

Fe 2 0 3 (%) 2.10 0.45 93.5

Si0 2 (%) 1 1.6 39.9 <1

Zr0 2 (%) 5.37 12.07 30.6

P2O5 (%) 0.199 0.075 88.4

Al 2 0 3 (%) 2.01 1 .51 77.0

Nb 2 0 5 (%) 0.264 0.136 84.2

Cr 2 0 3 (%) 0.072 0.38 83.6

Example 4

A rutile and anatase concentrate was milled and mixed with concentrated sulphuric acid at a mass ratio of 1.5 acid to 1 ore. The resulting mixture was baked at 180°C for twelve (12) hours to produce a sulphate cake. The cake was dissolved with 10% sulphuric acid to produce a solution of titanyl sulphate. This resulted in a total extraction of 38% of anatase, 18% of rutile and 30.7% of total Ti0 2 . The feed and dissolution residue assays are provided in table 4.

Relative to examples 1 to 3, the further reduction in temperature to 180°C has resulted in very poor recovery of both anatase and rutile, despite the 12 hour duration.

Table 4: Feed and residue assays for Example 4

Example 5

A rutile and anatase concentrate was milled and mixed with concentrated sulphuric acid at a mass ratio of 1.0 acid to 1 ore. The resulting mixture was baked at 250°C for eight (8) hours to produce a sulphate cake. The cake was dissolved with 10% sulphuric acid to produce a solution of titanyl sulphate. This resulted in a total extraction of 93% of anatase, 74% of rutile and 74.3% of total Ti0 2 . The feed and dissolution residue assays are provided in table 5.

Relative to example 1 , this example demonstrates how reduction in acid relative to ore to merely stoichiometric proportions significantly affects both anatase and rutile dissolution and recovery.

Table 5: Feed and residue assays for Example 5

AI 2 o 3 (%) 2.01 1 .184 76.7

Nb 2 o 5 (%) 0.264 0.182 72.7

Cr 2 0 3 (%) 0.072 0.045 75.5

Example 6

A rutile and anatase concentrate was milled and mixed with concentrated sulphuric acid at a mass ratio of 1.0 acid to 1 ore. The resulting mixture was baked at 220°C for twelve (12) hours to produce a sulphate cake. The cake was dissolved with 10% sulphuric acid to produce a solution of titanyl sulphate. This resulted in a total extraction of 92%) of anatase, 70% of rutile and 72.0% of total Ti0 2 . The feed and dissolution residue assays are provided in table 6.

This example, relative to example 5, highlights how lower temperature can be balanced by longer duration of treatment.

Table 6: Feed and residue assays for Example 6

Example 7 A rutile concentrate was milled and mixed with concentrated sulphuric acid at a mass ratio of 1 .5 acid to 1 ore. The resulting mixture was baked at 250°C for eight (8) hours to produce a sulphate cake. The cake was dissolved with 10% sulphuric acid to produce a solution of titanyl sulphate. This resulted in a total extraction of 73% of rutile and 70.9% of total Ti0 2 . The feed and dissolution residue assays are provided in table 8.

This example indicates lower recovery of rutile where anatase is not present than for the mixed ore of example 1.

Table 7: Feed and residue assays for Example 7

It will be understood that the invention disclosed and defined in this specification extends to all alternative combinations of two or more of the individual features mentioned or evident from the text or drawings. All of these different combinations constitute various alternative aspects of the invention.