Technical Field

The present disclosure relates to methods and systems for the extraction of lithium from a lithiferous species such as lithiferous ore.

Background

The transition away from non-renewable energy sources has seen an increase in the use of battery technologies to store electricity generated by renewable sources such as solar and wind. Bateries are now used to power vehicles, houses, and industrial sites, as both backup and primary power sources. Although several battery technologies can be utilised for such batteries, those based on lithium have shown the greatest commercial success due to the energy densities provided by lithium-based bateries. Future demands for lithium for lithium-ion batteries are expected to exceed supply.

Brines (saiars and lakes) were originally the main source of lithium, but the demand for lithium has resulted in the rapid growth of extracting lithium from lithiferous ores.

Pegmatite ores containing spodumene (LIAISI ₃ AI) and petalite (LIAISI ₄ O ₁₀ ) are now commonly ores used in the extraction of lithium. Although the production of lithium from pegmatite ores is relatively costly relative to extraction from brines, the process allows faster production of lithium chemicals with high extraction efficiency and purity. Nonetheless., despite being able to utilise pegmatite ores, the demand for lithium remains high which has increased the focus on using “secondary'’ lithium ores such as mica-based ores such as lepidolite ((K(LI,AI)3(AI,SI))4O ₁₀ (F,OH) ₂ ). However, the process of extracting lithium from these secondary ores is more complex than that for spodumene and petalite pegmatite ores.

It is to be understood that, if any prior art publication is referred to herein, such reference does not constitute an admission that the publication forms a part of the common general knowledge in the art, in Australia or any other country.

Summary

An embodiment provides a method of treating a lithiferous species such as lithiferous ore or iithiferous concentrate, comprising:

(I) roasting the Iithiferous species with one or more alkali salts to form a roasted Iithiferous species;

(ii) treating the roasted Iithiferous species with a leaching solation to form a leach liquor comprising a water- soluble lithium species:

(ill) adding a source of phosphate to the leach liquor to precipitate lithium phosphate; and

(iv) collecting solid lithium phosphate.

The one or more aikaii salts may include sodium sulphate, potassium sulphate, limestone, lime, gypsum and/or dolomite. The method may further comprise grinding the iithiferous species prior to step (ii) to reduce a particle size of the Iithiferous species. Grinding may be performed after step (I). Roasting may be performed at a temperature ranging from about 750°C to about 1,100°C Step (ii) may further comprise separating the roasted iithiferous species from the leach liquor.

The leaching solution may be water. The leach solution may include filtrates and washings from steps (iii) and/or (iv). Leaching may be performed at a temperature ranging from about 40°C to about 70°C. The water-soluble lithium species may include lithium sulphate and/or lithium hydroxide.

The method may further comprise prior to step (iii) removing non-iithium species from the leach liquor by precipitation Precipitation of non-lithium species may be performed by raising a pH of the leach liquor >9, such as ≥10.5. The non-iithium species may include transition metals, magnesium and calcium. Calcium may be precipitated by addition of a carbonate species.

Step 0v) may comprise washing the solid lithium phosphate with a water wash thereby forming a water wash filtrate Step (iv) may comprise washing the solid lithium phosphate with phosphoric acid wash thereby forming a phosphoric acid wash filtrate. Washing the solid lithium phosphate with phosphoric acid may compose forming a slurry of solid lithium phosphate and adding phosphoric acid to the slurry until a pH of the slurry is <5.4.

In an embodiment, the method may further comprise: collecting the water wash filtrate and collecting the phosphoric acid wash filtrate to form a filtrate stream; crystallising the filtrate stream to form a solid salt mixture; and using the solid salt mixture in step (i).

The source of phosphate may be added up to 10% excess. The source of phosphate may include trisodium phosphate and phosphoric acid. A temperature of the leach liquor In step (ill) may be ≥90°C, After step (ill) the leach liquor may have a lithium concentration of about 120 mg/L. After step (iii) the teach liquor may have a lithium concentration of equal to or greater than 120 mg/L.

'The lithiferous species may include, lepidolite, zinnwaldite and/or iithium-containing clays. The lithiferous species may include spodumene.

The method may further comprise (v) dissolving the solid lithium phosphate in sulphuric acid to form a solution of lithium sulphate and phosphoric acid, and then crystallising solid lithium sulphate from the solution of lithium sulphate and phosphoric acid to form a leachate comprising phosphoric acid. The phosphoric acid in the leachate comprising phosphoric acid may be collected and used in step (iii). The collected phosphoric acid may be combined with sodium hydroxide to form trisodium phosphate. The solid lithium sulphate may be crystallised as lithium sulphate monohydrate by heating the solution of lithium sulphate and phosphoric acid to a temperature above 50°C.

The method may further comprise dissolving the solid lithium sulphate to form a solution of lithium sulphate and combining the solution of lithium sulphate with a carbonate source to precipitate lithium carbonate from a barren liquor. The method may further comprise causticising the solid lithium sulphate by dissolving lithium sulphate to form a causticising solution and adding sodium hydroxide then crystalising lithium hydroxide, for example as lithium hydroxide monohydrate. In an embodiment, prior to adding the carbonate source or causticising, a pH of the carbonation solution or causticising solution may be raised with an alkali to precipitate lithium phosphate to remove any remaining phosphate, then collecting the precipitated lithium phosphate. The alkali may be added to the solution with dissolved lithium sulphate until a pH of 11 is reached.

An embodiment provides a method of treating a I ithiferous species such as lithiferous ore of lithiferous concentrate to form lithium carbonate, the method comprising: (I) roasting the iithiferous species with one or more alkali salts to form a roasted Iithiferous species;

(ii) treai-ng the roasted Iithiferous species with a leaching solution to form a leach liquor comprising a water-soluble lithium species:

(iii) adding a source of phosphate to the leach liquor to precipitate lithium phosphate,

(iv) converting the lithium phosphate to a water-soluble lithium salt and then crystallising or precipitating the water-soluble lithium salt to form solid water-soluble lithium salt and a filtrate;

(v) removing imparities from the solid water-soluble lithium salt; and

(vi) subjecting the purified solid water-soluble lithium salt from (v) to carbonation to form solid lithium carbonate.

In one or more embodiments, the filtrate from step (tv) may he used in step (iii) as at least part of the source of phosphates

In one or more embodiments, step (ii) may include removing solids from the leach liquor to form a first filtrate product. Ths first filtrate product may be treated with lime to raise a pH of the leach liquor to precipitate metal hydroxide impurities. The pH may be raised above 9. The metal hydroxide impurities may include those based on Al, Mn, Fe and Mg. Fluoride may also be removed from the first filtrate product by addition of phosphoric acid to precipitate fiuoride-containing species, such as fluorapatite. Following precipitation of metal hydroxide impurities and fiuoride-containing minerals, the first leachate product may be filtered to remove residue and form a second filtrate product A oarbonate source such as sodium carbonate may be added to the second filtrate product to precipitate calcium species, such as calcite. The second filtrate product may be filtered to remove precipitated calcium species to form a polished liquor solution. The polished liquor solution may then be used in step (iii).

In an embodiment, step (ii) includes; filtering the leach liquor to form a first filtrate product; raising a pH of the first filtrate product to precipitate metal hydroxide impurities; precipitating fiuoride-containing species; filtering the first filtrate product to remove precipitated metal hydroxide impurities and fiuoride-containing species to form a second filtrate product; adding a carbonate source to the second filtrate product to precipitate caloium-containing species; and filtering the second filtrate product, to remove the precipitate caloium-containing species to form a polished leach liquor. In an embodiment, step (iv) may include dissolving the solid lithium phosphate in sulphuric acid to form a solution of iithium sulphate and phosphoric acid, and then precipitating solid lithium sulphate, such as lithium sulphate monohydrate, from the solution of iithium sulphate and phosphoric acid to form a leachate comprising phosphoric acid. The leachate -comprising phosphoric acid may be treated with an alkali hydroxide to convert the phosphoric acid to trisodium phosphate. in an embodiment: step (v) includes dissolving the solid lithium salt to form a lithium- containing solution and precipitating cation and/or anion impurities from the I ithiurn- containing solution.

Step (III) may include forming a filtrate comprising mixed salts that may be added to roasting at step (I). The filtrate comprising mixed salts may be treated to form mixed salt solids, such as by crystallisation. A filtrate formed from collecting solid iithium carbonate may be recycled back to step (iii). The filtrate formed from collecting solid iithium carbonate may be used to form a solution used during step (iii).

Step (vi) may include combining a iithium-rich solution of the purified lithium salt and a source of carbonate to precipitate lithium carbonate The method may further comprise heating the Iithium-rich solution to promote precipitation of lithium carbonate. The iithium-rich solution may be heated to >60°C. The purified lithium salt may be lithium sulphate. In an embodiment, steps (i)-(iii) may be as set forth above.

Brief Description of the Drawir

Embodiments of the disclosure will now be described, by way of example only, with reference to the accompanying non- limiting drawings, in which:

Figure 1 is an embodiment of a process flow diagram.

Figure 1a is an embodiment of a purification step prior to precipitation of iithium phosphate

Figure- 2 is an embodiment c-f a process flow diagram.

Figure 3 is an embodiment of an industrial process flow diagram.

Detailed Description A method or process 10 of treating a Iithiferous ore or concentrate is shown in Figure 1. The Iithiferous ore or concentrate can include spodumene, lepidolite, zinnwaldite, lithium-containing days, and/or other lithium-containing materials. In an embodiment, the iithiferous ore or concentrate is a secondary iithiferous ore. For example, in an embodiment, the Iithiferous ore is non-spodumene ore.

The process 10 includes the steps of roosting 12, leaching 14, filtering 16, lithium phosphate precipitation 18, and collection of lithium phosphate 20, Each of steps 12, 14, 16, 18, and 20 will now be described in more detail, it should be appreciated that the steps described herein may be performed In their own reactor, vessel, tank, or the like, or may include a plurality of reactors, vessels, tanks, or the like, and that reference to processing steps does not limit the disclosure to specific reactors, vessels, tanks, or the like. During roasting 12. iithiferous ore is roasted with one or more alkali salts to form a roasted ore. The alkali salts can include sodium sulphate, potassium sulphate, limestone, lime, gypsum and/or dolomite. Gypsum (calcium sulphate) and sodium sulphate can be a hydrate or an anhydrite. The specific ratio of the alkali salts will be dependent on the roasting conditions and the make-up or composition of the Iithiferous ore or concentrate. For example, an embodiment of an alkali salt mixture is shown in

Table 1 . in an embodiment, the total water content of the alkali salt mixture is up to 25%. In an embodiment, the total water content of the alkali salt mixture is 19%. The inclusion of water in the alkali salt mixture can help to enhance contact of reagents with the Iithiferous ore.

Table 1 : Composition of alkali salt mixture relative iithiferous ore or concentrate (dry),

The alkali salts may be combined or blended in an appropriate mixer to ensure homogeneity of the mixture. The iithiferous ore may be combined with the alkali salts before blending to ensure the iithiferous ore and alkali salts are homogenised. The blended mixture of Iithiferous ore and alkali salts may be pelletised er agglomerated before roasting to reduce the effect of fines in the kiln to reduce losses to dust.

The mixture of alkali salts can be added as fresh and/or dry reagents or recycled from the process streams containing mixed alkaline salts, in an embodiment, the mixture of alkali salts is formed from fresh and/or dry reagents and/or mixed alkali salts recycled from one or more steps in the process 10. For example, following collection of lithium phosphate 20. a filtrate generated from collecting lithium phosphate can be crystallised or filtered (i.e. purified) during crystallisation or filtration 22 to alkali salts present in the filtrate, and this filtrate can be added during the roasting step 12. Note that crystallisation or filtration 22 is not required in all embodiments. in an embodiment, the dry reagents used in the alkali salt mixture have a particle size less than a particle size of the Iithiferous ore. Such a relative particle size can help to allow suitable contact and subsequent reaction during roasting 12. in an embodiment, the Iithiferous ore is ground to P ₁₀₀ of <250 pm prior to roasting 12. In an embodiment, the Iithiferous ore is ground to P ₁₀₀ of <90 pm prior to roasting 12. It should be appreciated that the P ₁₀₀ value will vary depending upon the properties of the Iithiferous ore , the particle liberation characteristics of the source ore and the processing method far that liberation and beneficiation, and the nature of the chemical reaction initiated by the heat of the kiln in the presence of the roasting reagents.

Roasting 12 may be performed at a temperature ranging from about 750°C to about 1,100°C. In an embodiment, roasting is performed between 875 and 975 °C. Roasting may be performed far a period ranging from about 30 minutes to about 180 minutes. Roasting may be performed for a period ranging from about 30 minutes to about 150 minutes. Roasting may be performed far a period ranging from about 30 minutes to about 120 minutes, in an embodiment, roasting a lithium-mica mixture at a temperature of around 875°C for 1 hour yielded lithium extraction of over 92% during leashing 14.

In an embodiment, process 10 includes the step of grinding 24 after roasting 12 to reduce the particle size of the roasted ore. The roasted ore can be ground to increase the contact of the particles during leaching 14 to enhance the extraction of lithium. In an embodiment, the roasted ore is ground to P ₁₀₀ of 200 μm. However, the friable nature of the roast ore may allow direct leaching without grinding. Accordingly, grinding 24 after roasting 12 is not required in all embodiments.

Following roasting 12, and optionally grinding 24 if required, the roasted ore is then subject to leaching 14 with a leaching solution to form a teach liquor such as a pregnant liquor solution (PLS) comprising a water-soluble lithium species. In an embodiment, the leaching solution is residue filtration wash. In an embodiment, the lithium is extracted into the leachate as lithium hydroxide and/or lithium sulphate. Put another way, the leachate may be enriched with lithium sulphate and/or lithium hydroxide, In an embodiment., the leachate following teaching 14 has a lithium-ion concentration ranging from about 1000 ppm to 12000 ppm. in an embodiment, the leachate following leaching 14 has a lithium-ion concentration ranging from about 1000 ppm to 10000 ppm. In an embodiment, the leachate following leaching 14 has a lithium-ion concentration ranging from about 1000 ppm to 7000 ppm. In an embodiment, the leachate following leaching 14 has a lithium-ion concentration ranging from about 1000 ppm to 5000 ppm. In an embodiment, the leachate following leaching 14 has a lithium-ion concentration ranging from about 2000 ppm to 4000 ppm. In an embodiment, the leachate following teaching 14 has a lithium-ion concentration ranging from about 3000 ppm to 4000 ppm. in an embodiment, the leachate following teaching 14 has a lithium-ion concentration of about 4000 ppm.

Leaching 14 may include one or more washing steps. In an embodiment, teaching 14 is performed at a temperature ranging from about 40°C to about 70°C. in an embodiment, leaching 14 is performed at solid content, ranging from 30 wt% and 50 wt.%. In an embodiment, teaching 14 is performed at solid content ranging from 40 wt% and 50 wt%. m an embodiment, leaching 14 is performed at a solids content of about 45 wt%. An advantage of using a higher solids content during teaching 14 and subsequent washing is that it may increase the lithium tenor.

The pregnant liquor solution formed from teaching 14 is subject to filtration 16 e.g. to remove solid residue. Filtration 16 may include removal of non-lithium species from the pregnant liquor solution, for example by precipitation, during filtration 16. In an embodiment, precipitation is performed by raising a pH of the pregnant liquor solution >10.5 prior to filtration 16. The non-lithium species may include transition metals, magnesium and calcium. Fluorine may be removed by adding phosphoric acid. Calcium may be precipitated by the addition of a carbonate species. In this way, filtration 16 acts to remove impurities from the pregnant liquor solution and may include several filtration steps.

Filtration 16 may include polishing of the pregnant liquor solution, in Figure 1 , a pregnant liquor polishing process 30 is shown generally, which is described in more detail with reference to Figure 1a. Following filtering at step 16, further solids can be removed to form a first filtrate product which may include Impurities such as non-lithium species including water-soluble forms of Al, Mn, Fe and Mg. . The impurities in the first filtrate product are precipitated at step 32 by Increasing a pH of the first filter product to be >9.0, such as ≥10,5 to form insoluble metal hydroxides (i.e. precipitates). In an embodiment, a pH of the first filter product is increased by the addition of lime. Phosphoric acid can also be added at step 32 to remove any fluorine or fluoride- containing species from solution e.g. by precipitating fluorapatite. The amount of phosphoric acid added to remove fluorine is such that it prevents the precipitation of lithium phosphate and/or solubilisation of the insoluble metal hydroxides. The first filtrate product is then filtered at step 34 to remove residue and precipitates to form a second filtrate product. If lime is used to increase the pH of the first filtrate product, the second filtrate product contains calcium or a calcium-containing species, in such instances, a carbonate source such as sodium carbonate may then be added to the second filtrate product at step 36 to remove calcium e.g. by the formation of calcite. The precipitated calcium is then filtered at step 38 to form a polished pregnant liquor solution. The polished pregnant liquor is then used in lithium phosphate precipitation at step 18. as described in more detail below. in an embodiment, leachate from filtration 16 is recycled back and used in leaching 14 and used as wash water during solid-liquid separation to remove entrained liquor and collect pregnant liquor solution enriched in lithium sulphate. The leachate from filtration 16 may be combined with water or may be used directly when recycled back and used in leaching 14. For example, leachate from filtration 16 may be used directly in a washing step.

Following filtration 16, and if performed polishing step 30, a source of phosphate is added to the pregnant liquor solution or polished pregnant liquor solution if polishing process 30 Is performed to precipitate lithium phosphate 18 i.e. solid lithium phosphate. The addition of a source of phosphate causes water-soluble lithium species such as lithium sulphate and lithium hydroxide to be converted to lithium phosphate. In an embodiment, the source of phosphate includes one or more of trisodium phosphate, alkaline phosphate sails, and phosphoric acid. In an embodiment, the source of phosphate is added in an equal stoichiometric amount relative to the lithium content of the pregnant liquor solution, in another embodiment, the source of phosphate is added in excess relative a lithium content of the pregnant liquor solution. Adding an excess of phosphate may help to maximise the precipitation of lithium ions from the pregnant liquor solution. In an embodiment, the source of phosphate is added in at leasti .02% stoichiometric excess of the lithium content of the pregnant liquor solution. In an embodiment, the source of phosphate is added in an amount ranging from 1% stoichiometric excess to 10% stoichiometric excess of the lithium content of the pregnant liquor solution. In an embodiment, the source of phosphate is added in an amount ranging from 1 % stoichiometric excess to 5% stoichiometric excess of the lithium content of the pregnant liquor solution, in an embodiment, the source of phosphate is added in an amount ranging from 2% stoichiometric excess to 5% stoichiometric excess of the lithium content of the pregnant liquor solution. In an embodiment, the source of phosphate is added in an amount ranging from 2% stoichiometric excess to 3% stoichiometric excess of the lithium content, of the pregnant liquor solution. In an embodiment, the source of phosphate is added in a 2.5% stoichiometric excess of the lithium content of the pregnant liquor solution.

Lithium phosphate precipitation 18 may occur at ambient temperature e.g. ~25°C. In an embodiment, lithium phosphate precipitation 18 occurs at an elevated temperature e.g. >35°C. in an embodiment, lithium phosphate precipitation 18 occurs at a temperature above 40°C. In an embodiment, lithium phosphate precipitation 18 occurs at a temperature above 45°C. In an embodiment, lithium phosphate precipitation 18 occurs at a temperature above 50°C. in an embodiment, lithium phosphate precipitation 18 occurs at a temperature above 55%. In an embodiment, lithium phosphate precipitation 18 occurs at a temperature above 60%. In an embodiment, lithium phosphate precipitation 18 occurs at a temperature above 65°C. in an embodiment, lithium phosphate precipitation 18 occurs at a temperature above 70%. In an embodiment, lithium phosphate precipitation 18 occurs at a temperature above 75%. In an embodiment, lithium phosphate precipitation 18 occurs at a temperature above 80°C. In an embodiment, lithium phosphate precipitation 18 occurs at a temperature above 85%. In an embodiment, lithium phosphate precipitation 18 occurs at a temperature above 90°C. In an embodiment, lithium phosphate precipitation 18 occurs at a temperature ranging from 60°C to >90%. In an embodiment, lithium phosphate precipitation 18 occurs at a temperature at or below a boiling point of the pregnant liquor solution.

Lithium phosphate precipitation 18 may include contacting the pregnant liquor solution with the source of phosphate with a residence time of 10 minutes. Lithium phosphate precipitation 18 may include contacting the pregnant liquor solution with the source of phosphate with a residence time of 15 minutes. Lithium phosphate precipitation 18 may include contacting the pregnant liquor solution with the source of phosphate with a residence time of 20 minutes. Lithium phosphate precipitation 18 may include contacting the pregnant liquor solution with the source of phosphate with a residence time of 25 minutes. Lithium phosphate precipitation 18 may include contacting the pregnant liquor solution with the source of phosphate with a residence time of 30 minutes. Lithium phosphate precipitation 18 may Include contacting the pregnant liquor solution with the source of phosphate with a residence time of 40 minutes Lithium phosphate precipitation 18 may include contacting the pregnant liquor solution with the source of phosphate with a residence time of 50 minutes. Lithium phosphate precipitation 18 may include contacting the pregnant liquor solution with the source of phosphate with a residence time of 60 minutes. A range of residence times may be used depending on the properties of the sithrfemus ore and the composition and concentration of the pregnant liquor solution.

Foilowing precipitation of lithium phosphate, the treated pregnant liquor solution may have a lithium concentration of up to 120 mg/L (120 ppm). In this way, lithium phosphate precipitation 18 may result in the recovery of >90% of lithium in the pregnant liquor solution. In an embodiment, lithium recovery is >95%. In an embodiment, lithium recovery ranges from 95% to 98%.

Once precipitated, the lithium phosphate is collected at step 20. Lithium phosphate can be collected by filtration. The filtered lithium phosphate may be washed. The lithium phosphate may be washed with water. Washing may be achieved by forming a slurry of lithium phosphate, in an embodiment, filtered (i.e. solid) lithium phosphate is washed twice with water using a ratio of [water]: [LI ₃ PO ₄ ] of 1:1. Washing may be performed at elevated temperatures e.g. 40°C. In an embodiment, washing is performed at 60°C. Additives may be added to the water used to wash the lithium phosphate. For example, phosphoric acid can be added to the slurry of water and phosphoric acid until a pH of the slurry is <5.4. The lithium phosphate collected at step 20 may be purified to form battery-grade lithium phosphate. Optionally, the step of collecting lithium phosphate 20 may Include a purification step that upgrades crude lithium phosphate to battery-grade lithium phosphate.

In an embodiment, the filtrate 21 from filtered lithium phosphate is collected and recycled. For example, and as shown in Figure 1 , the filtrate 21 car; be subject to crystallisation and/or filtration at step 22. The products of crystallisation and/or filtration 22 can be considered as forming a secondary stream of alkali salts. The secondary stream of alkali salts may include sodium sulphate, potassium sulphate and rubidium sulphate. In the embodiment shewn in Figure 1. the products of crystallisation and/or filtration 22 are recycled back into roasting 12 via recycling stream 26 to replace the sodium sulphate used in roasting, in an embodiment, part of the recycle stream 26 is bled at step 28 to remove or reduce the amount of recycle stream 26 being delivered back to the alkali salt roast 12. The bleed 28 may be performed on a predetermined cycle. For example, once the filtrate 21 has been recycled a predetermined number of times, some or all of the recycle stream 26 is discharged from the system 10. As another example, after a predetermined volume of filtrate has passed through the crystallisation or filtration step 22, some or all of the recycle stream 26 is discharged from the system 10. The amount of discharge is typically supplemented by the addition of new reagents during the alkali roast 12, leaching 14, and/or lithium phosphate precipitation 18. The amount of bleed may depend on the rubidium in the recycle stream. The rubidium may be extracted for commercial benefit.

An advantage of precipitating lithium phosphate is that precipitation can be performed without concentration steps such as evaporation. Eliminating the need for concentration may help to reduce complexity and required energy inputs when extracting lithium from lithiferous ore. As described in more detail below, lithium phosphate is also a useful form of lithium that can be used to form more commonly traded forms of lithium such as lithium carbonate and lithium hydroxide. Using a source of phosphate to form lithium precipitate can simplify the extraction of lithium for secondary lithium ores.

A method or process 100 of treating a lithiferous ore or concentrate to form lithium carbonate will now be described with reference to Figure 2. The process 100 forms lithium carbonate using a lithium phosphate intermediate. Process 100 utilises process 10 to form lithium phosphate. Process 100 starts with lithiferous ore that is subject to alkali salt roast 12, teaching 14, filtering 16. lithium phosphate precipitation 18. collection of lithium phosphate 20, and if used crystallisation or filtration of filtrate 22. from process 10 as described above to form lithium phosphate.

The lithium phosphate is then subject to dissolution and crystallisation 110. Dissolution is typically achieved using an acid, in an embodiment, sulphuric acid is used to dissolve lithium phosphate to form a solution of lithium sulphate and phosphoric acid, The lithium phosphate may be slurried or repulped prior to dissolution, in an embodiment, the lithium phosphate is slurried or repulped In water up to 30wt% solids, in an embodiment, the lithium phosphate is slurried or repulped in water up to 20wt% solids, in an embodiment, the lithium phosphate is slurried or repulped in water at 5wt% or more solids, hi an embodiment, the lithium phosphate is slurried or repulped in water at 10wt% or more solids, in an embodiment, the lithium phosphate is slurried or repulped in water at 15wt’% or more solids. In an embodiment, the lithium phosphate is slurried or repulped in water at 10wt% to 20wt% solids. in an embodiment, sulphuric acid is added to a slurry of lithium phosphate until all of the lithium phosphate has dissolved. A concentration of the sulphuric acid may be

98%. embodiment, sulphuric acid is added until the sulphate content is at least stoichiometric with the lithium content, in an embodiment, sulphuric acid is added until the sulphate content is mere than the lithium content. Adding the sulphuric acid in excess can help to ensure complete conversions of lithium phosphate to lithium sulphate. The sulphuric acid may be added until the sulphate content Is in 1 % excess of the lithium content. The sulphuric acid may be added until the sulphate content is in 2% excess of the lithium content. The sulphuric acid may be added until the sulphate content is in 3% excess of the lithium content. The sulphuric acid may be added until the sulphate content is in 4% excess of the lithium content. The sulphuric acid may he added until the sulphate content is in 5% excess of the lithium content.

Once lithium phosphate has been dissolved to form a water- soluble lithium salt, the water-soluble lithium salt is then crystaiised or precipitated. In embodiments where sulphuric acid is used to dissolve the irthium phosphate, lithium sulphate can be crystallised. In an embodiment, lithium sulphate is crystallised from the liquor by evaporation. For example, water can be evaporated from the liquor until approximately 90% of the water is evaporated thereby leaving crystaiised lithium sulphate. The % amount of the water evaporation may depend on the concentrations of the components in the solution, in an embodiment, the liquor is evaporated until 50%, 60%, 70%, 80%, 90% or >90% of the water is evaporated. Evaporation can be carried out at atmospheric pressures. However, evaporation may also be carried out under reduced pressure, for example to speed up evaporation or to reduce a temperature required for evaporation. The lithium sulphate formed from crystallisation may be lithium sulphate monohydrate (Li ₂ SO ₄ H ₂ O), Seeding may be used to initiate crystallisation of lithium sulphate.

Evaporation of liquor to crystallise lithium sulphate may be achieved by heating the liquor. In an embodiment, the liquor is heated above 40°C to crystaiise lithium sulphate. In an embodiment, the liquor is heated above 50°C to crystaiise lithium sulphate. In an embodiment, the liquor is heated above 60°C to crystaiise lithium sulphate. In an embodiment, the liquor is heated above 70°C to crystals® lithium sulphate. In an embodiment, the liquor is heated above 80°C to crystaiise lithium sulphate, in an embodiment, the liquor is heated above 90°C to crystaiise lithium sulphate. In an embodiment, the liquor is heated to about 100°C to crystaiise lithium sulphate. In an embodiment, the liquor is heated at a temperature ranging from 50°C to 100°C to crystaiise lithium sulphate, in an embodiment, the liquor is heated at a temperature ranging from 60°C to 100°C to crystalise lithium sulphate. In an embodiment, the liquor is heated at a temperature ranging from 70°C to 100°C to crystaiise lithium sulphate, in an embodiment, thel liquor is heated at a temperature ranging from 80°C to 100°C to crystaiise lithium sulphate. In an embodiment, the liquor is heated at a temperature ranging from 90°C to 100°C to crystaiise lithium sulphate.

Once the lithiums phosphate has been dissolved to form a water-soluble lithium salt and then crystaiised, the solid lithium salt is filtered from the liquor at filtration 112 which forms filtrate stream 122. When acid is used to dissolve lithium phosphate at crystallisation 110, the filtrate stream 122 includes phosphoric acid. Any phosphoric acid present in filtrate stream 122 can be recycled back to lithium phosphate precipitation at step 18. In the embodiment shown in Figure 2, the filtrate stream 122 passes through phosphate regeneration 118. In an embodiment, phosphate regeneration 118 includes adding sodium hydroxide to the phosphoric acid to form trisodium phosphate. The regeneration stream that comprises trisodium phosphate is shown as regeneration stream 124, which is fed directly to lithium phosphate precipitation 18. Phosphate regeneration 118 is not required in ail embodiments. For example, phosphoric acid from filtrate stream 122 can be directly added to lithium phosphate precipitation 18, with sodium hydroxide being added at lithium phosphate precipitation 18 to generate trisodrum phosphate, if required, to facilitate precipitation of lithium phosphate. in an embodiment. the lithium sulphate product collected at filtration 112 is washed in a saturated lithium sulphate solution to remove entrained phosphate and other impurities. For example, the washing and filtration are conducted twice at a [solids][ liquid] wash ratio of 1 :1 and ambient temperature.

Recycling any phosphoric acid present in the filtrate from filtration 112 can help to reduce the required input amount of phosphate required to form lithium phosphate Following filtration 112, impurities can be removed at impurity removal 114 if required to form a purified lithium salt. The impurity removal 114 helps to polish and remove any residual phosphate and other impurities in the lithium sulphate following filtration 112. in an embodiment, crystallised lithium sulphate is dissolved in water and the pH is adjusted to 12 to precipitate and remove any impurities. Fur example, any phosphate present in the crystallised lithium sulphate can be precipitated as lithium phosphate once the pH is adjusted to alkaline conditions. Likewise, impurity removal 114 may involve precipitating cation and/or anion impurities. Any precipitate or solids formed during impurity removal 114 can be filtered off. In an embodiment, any source of phosphate collected during impurity removal 114 is recycled back to lithium phosphate precipitation 18 (not shown). The filtered residue from impurity removal 114 may contain high lithium content e g. 18 wt.% Li. Note that impurity removal 114 is not required in all embodiments, for example if the lithiferous ore is of high grade and/or the solids collected at filtration 112 are of sufficient purity. Following filtration 112, or if needed impurity removal 114, the source of lithium liquor is then subject to carbonation 116. Carbonation 116 can be achieved by lithium salt in the form a lithlum -containing solution such as a lithium-rich solution and then adding a carbonate source or carbonate salt. The carbonate salt may be sodium carbonate. 'The carbonate source may be dosed at a concentration of at least 100 g/L The carbonate source may be dosed at a rate of at least 150 g/L. The carbonate source may be dosed at. a rate of at least 200 g/L The carbonate source may be dosed at a rate of at least 250 g/L. The carbonate scarce may be dosed at a rate of at teas! 300 g/L The carbonate source may be dosed at a rate of about 100 g/L to 400 g/L. The carbonate source may be dosed at a rate of about 200 g/L to 400 g/L. The carbonate source may be dosed at a rate of about 250 g/L to 350 g/L. The carbonate source may be dosed at a rate of about 275 g/L to 325 g/L The carbonate source may be dosed at a rate of about 300 g/L.

Carbonation 116 may include heating the solution of lithium salt and carbonate source to promote precipitation of lithium carbonate. Carbonation may be performed at a temperature above about 50°C. Carbonation may be performed at a temperature above about 60°C. Carbonation may be performed at a temperature above about 70°C. Carbonation may be performed at a temperature above about 80°C. Carbonation may be performed at a temperature of about 90°C. Carbonation may be performed at a temperature ranging from about 50°C to about 100°C. Carbonation may be performed at a temperature ranging from about 60°C to about 100°C. Carbonation may be performed at a temperature ranging from about 70°C to about 100°C. Carbonation maybe performed at a temperature ranging from about 80°C to about 100°C. Carbonation 116 proceeds at aikaii pH. In an embodiment the pH during carbonation is >9. In an embodiment, the pH during carbonation Is >10. In an embodiment, the pH during carbonation is >11. In an embodiment, the pH during carbonation ranges from 10 - 12. In an embodiment, the pH during carbonation is about 11,

Following carbonation 116, lithium carbonate is collected at step 120. Collection of lithium carbonate at step 120 can include washing the lithium carbonate. The lithium carbonate may be washed with carbonation liquor. The lithium carbonate may be washed with water. The lithium carbonate may be washed with [solid]:[liquid] ratio of 1:2 - 1 :1. The lithium carbonate may be washed with [solid]: [liquid] ratio of 1:1.75 - 1:1. The lithium carbonate may be washed with [solid]:[liquid] ratio of 1 :5 - 1:1. The lithium carbonate may be washed with [ solid]:[liquid] ratio of 1 :1.25 - 1:1. The lithium carbonate formed by process 100 may be crude. The crude lithium carbonate may be purified to form battery-grade lithium carbonate.

The carbonation filtrate stream 126 from washing lithium carbonate during collection of lithium carbonate at step 120 can be recycled, either partially or entirely, back to lithium phosphate precipitation 18 to capture any water-soluble lithium present. Returning carbonation filtrate stream 126 back to lithium phosphate precipitation 18 helps to improve the lithium recovery from the process 100. in an embodiment, the carbonation f-ltrate stream 126 recycled to the lithium phosphate precipitation 18 may be conditioned to remove carbonate. In an embodiment, carbonation filtrate stream conditioning is carried out by reducing the pH of the carbonation filtrate stream 126 to 3 with an acid such as sulphuric acid to drive off carbonate as CO ₂ gas, and then raising a pH of the carbonation filtrate stream 126 with an alkaline source such as NaOH to high pH (e.g. >9} before being returned to phosphate precipitation 18. in an embodiment, the lithium carbonate coliected at step 120 is subjected to liming to form lithium hydroxide. instead of carbonation 116 to form lithium carbonation, the lithium suiphate from filtration 112 or optionally from impurity removal 114 can be causticised (i.e. subject to causticisation), for example with sodium hydroxide, to form lithium hydroxide. Causticisation would replace carbonation 116 and may be performed using known methods.

Examples

An example embodiment of a method of treating a ilthiferous ore to form lithium carbonate with now be described with reference to Figure 3 and process 200. Process 200 incorporates steps from process 100 where like reference numbers are used to describe the same or similar steps.

Lithiferous ere such as zinnwaldite is mixed with gypsum, caicite. sodium sulphate, and water according to the ratios and order listed in Table 2 and roasted at a temperature ranging from 875°C to 975°C for 30-60 minutes in roast step 12. Following roasting 12, if required the roasted ore is subject to grinding to PI 00 of 200 pm depending on roasted ore properties.

Table 2: Composition of alkali sail mixture relative lithiferous ore.

The roasted ore is then leached with wafer at step 14 at a temperature ranging from 40°C to 70°C to extract lithium sulphate and lithium hydroxide from the roasted ore

The teach slurry is then filtered off, has a solids content of about 44% and is filtered off and washed with water 208. Following washing, the residua 210 is discarded from the process 200. The filtrate from filtration 16 is then subject to polishing (e.g. polishing process 30) by:

I removing solids from teaching 14 to form a first filtrate product;

IL treating the first filtrate product with lime to raise the pH to remove metai impurities from solution (e.g. AL Mn, Fe Mg) by formation of insoluble metal hydroxides followed by addition of phosphoric acid (2g/L) to remove any fluorine by precipitation of fluorapatite ;

Ill filtering to remove residue and form a second nitrate product; iv adding sodium carbonate to the second filtrate product to remove calcium by precipitating calcite, v, filtering following sodium carbonate to remove residue and form a polished pregnant liquor solution.

Trisodium phosphate (and/or other alkaline phosphate salts and/or phosphoric acid) is then added to the leachate from filtration 16 at phosphate conversion 18 (i.e. lithium phosphate precipitation), and the resulting solution heated ≥90°C to precipitate lithium phosphate, which is then collected and washed twice with water at a [solid]: [water] ratio of 1:1 at a temperature of 60°C for 60 minutes. Following precipitation of lithium phosphate, the lithium content of the solution drops from about 4000mg/L to about 120mg/L..

The lithium phosphate from step 18 is filtered off at filtration 212. The filtrate including washings from filtration 212 is collected and crystallised at step 22 to form a solid salt mixture that includes sodium sulphate, potassium sulphate and rubidium sulphate. This solid salt mixture is then recycled via recycle stream 26 back to the alkali roast 12. The ratio of the components used in Table 2 for roasting may be adjusted depending on the composition of the solid self mixture.

Collected lithium phosphate is repulped in water with a solids content of 10% - 20%. ulphuric acid (98%) is then added to the lithium phosphate pulp to perform acidbased dissolution and crystallisation 110 until the sulphate content is stoichiometric with the lithium content plus 2% excess to ensure complete conversion of lithium phosphate to lithium sulphate. Water is then evaporated at a temperature ranging from 70°C to 100°C, but generally closer to 100°C, until approximately 90% of the water is evaporated to crystallise lithium sulphate, generally in the form of sulphate monohydrate, at crystallisation step 214. The crystallised lithium sulphate is then filtered at filtration 112 and washed with saturated lithium sulphate The nitrate stream 122 from filtration 112 contains phosphoric acid and is then passed to phosphate regeneration 118 where sodium hydroxide is added to regenerate trisodium phosphate that is then passed via regeneration stream 124 to phosphate conversion 18.

Crystallised lithium sulphate is then polished at impurity removal 114 by dissolving the solids tn water at a temperature of 90°C and adjusting the pH to 11 with sodium hydroxide. Adjusting the pH causes any remaining water-soluble phosphates to precipitate as lithium phosphate. Any precipitated lithium phosphate can be recycled back to phosphate conversion 18. The solution is then filtered at. filtration 218 to remove the precipitate and the resulting lithium sulphate-rich filtrate is collected and passed to carbonation 116. A portion of the lithium sulphate-rich filtrate is typically recycled via stream 222 for washing at filtration 112.

During carbonation 116, sodium carbonate is added to the lithium-rich solution e.g. lithium sulphate-rich, at a dosing rate of 300 g/L and the solution is agitated at 90°C to increase lithium carbonate recovery by decreasing the solubility of the lithium carbonate. The lithium carbonate is then filtered at lithium carbonate filtration 220 and washed three times with water a [solids]: [water] wash ratio of 1:1.5 to 1:1. The filtrate from lithium carbonate filtration 220 is subject to conditioning to remove carbonate by first reducing a pH of the carbonation filtrate stream 126 to pH 3 with sulphuric acid to drive off carbonate as CO ₂ gas. and then raising a pH of the carbonation filtrate stream 126 with NaOH to high pH (e g. >9) before being returned to phosphate precipitation

18.

The overall conversion of lithium Torn iithiferous ere to lithium carbonate in process 100 arte process 200 follows equations 1-4.

In the claims that follow and in the preceding description of the disclosure., except where the context requires otherwise due to express language or necessary implioatiou, the word “comprise” or variations such as “comprises” or “comprising” is used in an inclusive sense, i.e. to specify the presence of the stated features but not to preclude the presence or addition of further features in various embodiments. Modifications and variations as would be apparent to a skilled addressee are deemed to be within the scope of the present disclosure.