EP4702175A1

EP4702175A1 - Processing of brines for lithium recovery

Info

Publication number: EP4702175A1
Application number: EP24795362.3A
Authority: EP
Inventors: Kausar Hitesh SHAH; David Robinson
Original assignee: Reed Advanced Materials Pty Ltd
Current assignee: Reed Advanced Materials Pty Ltd
Priority date: 2023-04-26
Filing date: 2024-04-24
Publication date: 2026-03-04
Also published as: CL2025003296A1; WO2024221046A1; AR132493A1

Abstract

The present invention relates to a method for the processing of lithium containing brines, the method comprising the method steps of: (i) Passing a lithium containing brine to a first sulfate removal step; (ii) Passing a product of step (i) to a boron removal step; (iii) Passing a product of step (ii) to an impurity removal step; (iv) Passing a product of step (iii) directly or indirectly to a first ion exchange step to remove divalent impurities; (v) Passing a product of step (ii) to a second ion exchange step to remove further boron impurities; (vi) Passing a product of step (v) to a second sulfate removal step; (vii) Passing a product of step (vi) to an electrolysis step to produce lithium hydroxide; and (viii) Passing a product of step (vii) to a crystallisation step to produce a lithium hydroxide monohydrate product.

Description

“Processing of Brines for Lithium Recovery”

Field of the Invention

[0001 ] The present invention relates to a method for the processing of brines for lithium recovery.

[0002] More particularly, the method of the present invention is intended for use in the production of a lithium bearing solution suitable for further processing by electrolysis. In turn, it is particularly intended that the processing by electrolysis of the lithium bearing solution provides a lithium hydroxide monohydrate product and/or a lithium carbonate product.

[0003] The present invention further relates to the production of a lithium hydroxide monohydrate and/or lithium carbonate product that is/are of battery grade.

Background Art

[0004] The current process employed by brine producers requires first the conversion of lithium containing brine to lithium carbonate, requiring treatment with sodium carbonate (soda ash) to precipitate the lithium carbonate. This lithium carbonate is then causticised using hydrated lime. This process is known to be expensive and it employs complicated process unit operations. The lithium carbonate produced in this manner by brine producers, using the soda ash reaction on a lithium chloride solution, produces technical grade lithium carbonate. The technical grade lithium carbonate in turn needs to be further purified using an expensive bicarbonation circuit.

[0005] Lithium containing brines obtained from solar brine ponds typically contain a number of impurities, present at what are considered by operators as high levels. As such, these lithium containing brines are not considered suitable for electrolysis.

[0006] In International Patent Application PCT/AU2019/051014 (WO 2020/069558) the present Applicant describes a method for the processing of brines prior to an electrolysis step, that method comprising a number of method steps, in series, in which a brine is directed to each of a first filtration step to remove sulfates, two ion exchange steps for divalent impurity removal and boron removal respectively, and subsequent electrolysis. The process described does not allow for a sufficient lowering of sulfate levels ahead of electrolysis, nor does it remove boron to adequately low levels, when presented with brines of a certain composition. Further, the process described requires stepwise production of lithium carbonate by way of a bicarbonate intermediate.

[0007] The method and products of the present invention have as one object thereof to overcome substantially one or more of the above mentioned problems associated with the methods and products of the prior art, or to at least provide useful alternatives thereto.

[0008] The preceding discussion of the background art is intended to facilitate an understanding of the present invention only. This discussion is not an acknowledgement or admission that any of the material referred to is or was part of the common general knowledge as at the priority date of the application.

[0009] Throughout the specification and claims, unless the context requires otherwise, the word “comprise” or variations such as “comprises” or “comprising”, will be understood to imply the inclusion of a stated integer or group of integers but not the exclusion of any other integer or group of integers.

[0010] Throughout the specification and claims, unless the context requires otherwise, the term “battery grade lithium carbonate” refers to a product having a purity of about 99.5% or higher. Similarly, the term “battery grade lithium hydroxide” refers to a product having a purity of about 99% or higher.

[0011 ] The term brine, or brines, or variations thereof, is to be understood to include a solution of alkali and/or alkaline earth metal salt(s) in water, of a natural or possibly industrial source, which in its broadest form includes at least salar brines, geothermal brines, and liquors from the processing of hard rock lithium minerals such as spodumene, lepidolite and zinnwaldite. The concentrations of the various salts can vary widely. The ions present in brines may include a combination of one or more of a monovalent cation, such as lithium, multivalent cations, monovalent anions, and multivalent anions. Further, it is to be understood that the term brine, or lithium containing brine, may include a solid product comprising a crude, or relatively impure, lithium salt, for example a lithium chloride salt.

Disclosure of the Invention

[0012] In accordance with the present invention there is provided a method for the processing of lithium containing brines, the method comprising the method steps of:

(i) Passing a lithium containing brine to a first sulfate removal step;

(ii) Passing a product of step (i) to a boron removal step;

(iii) Passing a product of step (ii) to an impurity removal step;

(iv) Passing a product of step (iii) directly or indirectly to a first ion exchange step to remove divalent impurities;

(v) Passing a product of step (ii) to a second ion exchange step to remove further boron impurities;

(vi) Passing a product of step (v) to a second sulfate removal step;

(vii) Passing a product of step (vi) to an electrolysis step to produce lithium hydroxide; and

(viii) Passing a product of step (vii) to a crystallisation step to produce a lithium hydroxide monohydrate product.

[0013] In one form of the present invention, the first sulphate removal step rejects about 50% of the sulphates present in the lithium containing brine.

[0014] Preferably, the first sulphate removal step comprises the precipitation of sulphate compounds.

[0015] In one form of the present invention, the first sulfate removal step comprises the addition of precipitating agent to the lithium containing brine to precipitate sulphate compounds. Preferably, the precipitating agent is barium chloride to precipitate barium sulphate. [0016] In one form of the present invention, the first sulfate removal step comprises subjecting the lithium containing brine to a concentration step to precipitate sulphate compounds. Preferably, the concentration step targets a lithium concentration of at least 50 g/L.

[0017] In one form of the present invention, boron removal step (iii) comprises a boron solvent extraction step. Preferably, the boron solvent extraction step comprises contacting the lithium containing brine with a an organic extractant suitable to extract boron.

[0018] In one form of the present invention, boron removal step (iii) reduces the boron concentration in the lithium containing brine solution to less than 100 mg/L. In one form of the present invention, boron removal step (iii) reduces the boron concentration in the lithium containing brine solution to less than 80 mg/L. In one form of the present invention, boron removal step (iii) reduces the boron concentration in the lithium containing brine solution to less than 60 mg/L. In one form of the present invention, boron removal step (iii) reduces the boron concentration in the lithium containing brine solution to less than 40 mg/L.

[0019] In one form of the present invention, impurity removal step (iii) removes divalent impurities from the lithium containing brine.

[0020] In one form of the present invention, impurity removal step (iii) comprises a precipitation step in which the lithium containing brine is contacted with an alkali to precipitate one or more impurities. Preferably, the precipitation step will precipitate one or more impurities as hydroxides. More preferably, the alkali is selected from lithium hydroxide, sodium hydroxide, calcium oxide, calcium hydroxide or magnesium hydroxide.

[0021 ] Preferably, the first ion exchange step (iv) removes divalent impurities selected from the group of calcium, magnesium, manganese, strontium, and barium. Still preferably, the ion exchange step (iv) removes the divalent impurities from the lithium brine to a level of less than 0.2 ppm. Still preferably, the ion exchange step (iv) removes the divalent impurities from the lithium brine to a level of less than 0.1 ppm. [0022] Preferably, the second ion exchange step (v) removes boron impurities from the lithium brine to a level of less than 1 ppm. More preferably, the second ion exchange step (v) removes boron impurities from the lithium brine to a level of less than 0.5 ppm. Still preferably, the second ion exchange step (v) removes boron impurities from the lithium brine to a level of less than 0.1 ppm.

[0023] In one form of the present invention, the first ion exchange step (iv) and the second ion exchange step (v) remove divalent impurities from the lithium brine to a level of less than 0.2 ppm and boron impurities from the lithium brine to a level of less than 1 ppm. Preferably, the first ion exchange step (iv) and the second ion exchange step (v) remove divalent impurities from the lithium brine to a level of less than 0.1 ppm and boron impurities from the lithium brine to a level of less than 0.1 ppm.

[0024] In one form of the present invention, the second sulfate removal step (vi) utilises nanofiltration. Preferably, the second sulfate removal step (vi) removes sulphates from the lithium brine to a level of less than 1 gpl. More preferably, the second sulfate removal step (vi) removes sulphates from the lithium brine to a level of less than 500 ppm.

[0025] Preferably, the crystallisation step (viii) comprises separation of the lithium hydroxide monohydrate product from a spent liquor. In one form, the present invention further comprises passing the spent liquor from the lithium hydroxide monohydrate crystallisation step (viii) to a carbonation step (ix) in which the spent liquor is reacted with carbon dioxide to precipitate lithium carbonate. The thus formed lithium carbonate is preferably then dried in a drying step (x).

[0026] In a further form, the present invention further comprises the dewatering and washing of the precipitated lithium carbonate ahead of the drying step (x).

[0027] In one form of the present invention, the lithium containing brine is passed to a silicon removal step prior to the first ion exchange step (iii). Preferably, the product of step (iii) is passed to the silicon removal step prior to the first ion exchange step (iii).

Brief Description of the Drawings [0028] The present invention will now be described, by way of example only, with reference to the accompanying drawing, in which:

Figure 1 is a flow-sheet of a method for the processing of lithium containing brines, the method being in accordance with one embodiment of the present invention;

Figure 2 is a plot of change in pH of the raffinate throughout the course of the boron solvent extraction trial; and

Figure 3 is a plot showing the impact of pH on the extraction of boron during the boron solvent extraction trial.

Best Mode(s) for Carrying Out the Invention

[0029] The present invention provides a method for the processing of lithium containing brines, the method comprising the method steps of:

(i) Passing a lithium containing brine to a first sulfate removal step;

(ii) Passing a product of step (i) to a boron removal step;

(iii) Passing a product of step (ii) to an impurity removal step;

(vi) Passing a product of step (v) to a second sulfate removal step;

(viii) Passing a product of step (vii) to a crystallisation step to produce a lithium hydroxide monohydrate product. [0030] In Figure 1 there is shown a flow-sheet representing a method 10 for the processing of lithium containing brines, the method 10 being in accordance with one embodiment of the present invention. The method 10 comprises the method steps of passing a lithium containing material, for example a raw brine 12, from an offloading and storage facility 14 to a first or primary sulphate removal step 16. In a preferred embodiment, the primary sulphate removal step 16 comprises the precipitation of sulphate compounds. In one embodiment, the first sulphate removal step 16 rejects about 50% of the sulphates present in the lithium containing brine. In an alternative embodiment, the first sulphate removal step 16 rejects 50% or more of the sulphates present in the lithium containing brine.

[0031 ] In one embodiment, the first sulphate removal step 16 comprises the contact of the lithium containing brine with a precipitating agent to precipitate a portion of the sulphates present in the lithium containing brine. In one embodiment, the precipitating agent is selected from one or more of barium chloride, calcium chloride, calcium hydroxide and strontium chloride. In a preferred embodiment, the precipitating agent is barium chloride.

[0032] In the embodiment shown in Figure 1 , a portion of the sulphates present in the lithium containing solution are precipitated as barium sulphate 18 through the addition of barium chloride 20.

[0033] The barium chloride 20 is preferably dosed as a solution and is understood to react with sulphates in the lithium containing brine as follows:

[0034] The dose rate of barium chloride is set below the stoichiometric requirement to ensure that no soluble barium passes downstream. As such, sulphate removal is incomplete in the first sulphate removal step 16. The first sulphate removal step 16 also receives sulphate reject or retentate 22 from a second sulphate removal step to be described hereinbelow. The return of sulphate reject 22 in this manner ensures that ultimately 100% of sulphate from the raw brine 12 reports to the barium sulphate 18 precipitated solid. This barium sulphate 20 is filtered, for example in candle filters, to separate waste solid from a sulphate-depleted filtrate 24.

[0035] In one embodiment, the first sulphate removal step 16 comprises subjecting the lithium containing brine to a concentration step to precipitate a portion of the sulphates present in the lithium containing brine. The concentration step comprises, for example, heating the lithium containing brine to boiling temperature to remove water from the lithium containing brine. Other concentration means known in the art may similarly be used to concentrate the lithium containing brine. It is envisaged that the concentration step will also result in the precipitation of a portion of other impurities, including sodium, potassium and magnesium. The concentration step should maximise the precipitation of impurity salts while minimising lithium losses, such as through the crystallisation of lithium salts or complexes.

[0036] In one embodiment, the concentration step targets a lithium concentration of at least 40 g/L. In one embodiment, the concentration step targets a lithium concentration of at least 50 g/L. In one embodiment, the concentration step targets a lithium concentration of at least 55 g/L. In one embodiment, the concentration step targets a lithium concentration of at least 60 g/L. In one embodiment, the concentration step targets a lithium concentration of at least 65 g/L. In one embodiment, the concentration step targets a lithium concentration of about 70 g/L.

[0037] In one embodiment, the concentration step targets a lithium concentration of between 40 g/L and 80 g/L. In one embodiment, the concentration step targets a lithium concentration of between 50 g/L and 80 g/L. In one embodiment, the concentration step targets a lithium concentration of between 50 g/L and 75 g/L.

[0038] It is envisaged that the first sulphate removal step 16 may comprise both a concentration step and the contact of the lithium containing brine with a precipitating agent. It is further envisaged that the concentration step may be conducted as an alternative to contact of the lithium containing brine with a precipitating agent.

[0039] The sulphate-depleted filtrate 24 is passed to a boron removal step. In the embodiment shown in Figure 1 , the sulphate-depleted filtrate 24 is passed to solvent extraction 26. Boron in the raw brine 12 is present as borate salts of lithium and other cations. The sulphate-depleted filtrate 24 must be acidified to convert all boron to boric acid (H3BO3) to allow extraction. This is achieved by addition of an acid solution, for example hydrochloric acid 34 to a pH of about 2.0. The solution is then contacted with an organic extractant suitable to extract boron. The loaded extractant may then be separated from the aqueous phase. A mixture of 2-ethylhexanol extractant with an aliphatic kerosene diluent, for example, may be utilised as the organic extractant in the solvent extraction 26. It is envisaged that a range of reagents known in the art, generally solvating reagents, may be utilised at various concentrations in a diluent, including aromatic containing diluents.

[0040] A solvent extraction circuit employed in solvent extraction 26 consists, for example, of 5 extraction stages, 1 scrub stage and 2 stripping stages. Each stage employs a conventional mixer settler, in which organic and aqueous phases are first mixed to react, then allowed to separate in a settler, with lighter organic phase floating above the heavier aqueous phase. In the extraction stages, boric acid is extracted from the aqueous phase into the organic. Some lithium also transfers to the organic. A boron-depleted aqueous solution 36, called raffinate, progresses to the next impurity removal stage. It is envisaged that boron levels in the boron-depleted aqueous solution 36 are, for example, less than about 40 mg/L.

[0041 ] The boron-loaded organic goes to a scrub stage in which it is mixed with aqueous sodium carbonate solution 38 to remove lithium. This scrub stage also serves to remove entrained chloride from the loaded organic. The resulting aqueous is returned to the solvent extraction feed aqueous. The scrubbed organic goes to the strip stages where it is mixed with a solution of sodium hydroxide 40. This reacts with boric acid to form an aqueous strip solution 27 of sodium borate (borax). Stripped organic is returned to the extraction stage, while the boron loaded aqueous solution is fed to the crystallisation step, to be described hereinbelow.

[0042] It is understood that carryover of organic downstream should be avoided. Organic can foul nanofiltration membranes and potentially also electrolysis membranes, although it is also understood that it is unlikely that any would pass through the brine evaporator. Organic may be both dissolved in the aqueous streams and entrained as a separate phase. Organic in the boron-depleted raffinate 36 is minimised by provision of a post-settler stage followed by carbon adsorption columns.

[0043] Strip solution 27 may be further treated to recover boron products, such as sodium borate. In the embodiment shown in Figure 1 , a sodium metaborate product 28 is crystalised from a loaded strip solution in a crystallisation step 30. The loaded strip solution 27 is first concentrated in an evaporation stage. The falling-film type evaporator is operated under vacuum to enable lower temperature. The process liquor passes through the tubes of a vertical heat exchanger, while heat is provided by steam condensing on the shell side. Liquid and vapour fall through the tubes and pass to a cyclonic separator. Vapours flow to a surface condenser while the concentrated liquor is recirculated through the tubes and pumped to the crystallisation step 30.

[0044] The preconcentrated liquor is flash cooled under high vacuum at around 30°C. The cooling crystalliser is a forced circulation (FC) type draft inlet crystalliser, where slurry is recirculated by an axial flow pump. The recirculating slurry flashes at the surface where crystal growth takes place. Slurry is pumped from the crystalliser and thickened in a hydrocyclone then dewatered in a centrifuge. Solid crystals are screw conveyed to a dryer. The centrate is a solution of sodium hydroxide and sodium metaborate, which is collected and returned to the solvent extraction strip circuit.

[0045] After crystallisation the sodium metaborate product 28 is dried, for example by way of a co-current rotary dryer 31 , and dry crystals are discharged to a bin for packaging 32.

[0046] It is envisaged that other boron removal means known in the art may be implemented in the boron removal step. In one embodiment, boron may be removed through the precipitation of boron containing solids such as calcium borate hydrate. It is envisaged that this could be achieved by increasing the solution pH to ~8.4 with suitable reagents.

[0047] The boron-depleted raffinate 36 is passed to an impurity removal step to remove a portion of impurities present in the boron-depleted raffinate 36. The impurities removed in the impurity removal step will depend on the particular lithium containing brine. However, it is generally understood that such brines can contain calcium, magnesium, iron, aluminium, potassium and/or strontium as impurities. The main impurities targeted in the impurity removal step are divalent elements impurities, particularly calcium and magnesium. It is envisaged that other impurities may also be removed in the impurity removal step.

[0048] The impurity removal step comprises one or more stages to reduce the concentration of impurities in the lithium containing brine. In one embodiment, the impurity removal step comprises the contact of the brine with an alkali to precipitate one or more impurities. In this context, the term “alkali” should be understood to be a basic, ionic salt of an alkali metal or an alkaline earth metal or a solution thereof. In the embodiment shown in Figure 1 , the impurity removal step comprises a precipitation step 42 that is conducted in two stages. In a first stage, lithium hydroxide 44 is added to raise the pH, and to precipitate magnesium, iron, aluminium, and strontium as hydroxides. It is envisaged that other alkalis, such as sodium hydroxide, calcium oxide or calcium hydroxide can similarly be used in the first stage to increase the pH and precipitate impurities. In a second stage, lithium carbonate 46 is added to further raise the pH and precipitate calcium as carbonate. It is envisaged that other carbonates, such as sodium carbonate, calcium carbonate or carbon dioxide can similarly be used in the second stage to increase the pH and precipitate impurities. Precipitation is preferably conducted at elevated temperature to promote removal of calcium. Heating is preferably achieved by passing the solution through heat exchangers in which hot filtrate and steam are used for heating. The heated solution passes into a train of agitated tanks where lithium hydroxide and lithium carbonate are added to raise the pH and force the divalent metals to precipitate as hydroxide and carbonate solids. Filter aid may also added to the tanks (termed ‘body feed’) to improve the filtration characteristics. It is to be understood that the precipitation step 42 may be undertaken in a single step or stage, for example by way of addition of only lithium hydroxide 44. It is envisaged that a single stage precipitation step 42 will provide a lesser dilution.

[0049] Both the lithium carbonate 46 and lithium hydroxide 44 reagents are produced in, and effectively recycled within, the method 10 of the present invention.

[0050] The first stage precipitation reactions are understood to proceed as follows:

AlCh (aq) + 3LiOH (aq) AI(OH)₃ (s) + 3LiCI (aq)

[0051 ] The second stage precipitation reaction is understood to proceed as follows:

[0052] It is not expected that barium will be present in the feed to the impurity precipitation step 42, although if too much barium chloride 20 had been added in the first sulphate removal step 16 it is expected that it would be precipitated together with other divalent metals in this step.

[0053] A slurry 48 resulting from precipitation step 42 passed to impurity removal filters 50 for separation of clear solution from the solids. The filters 50, for example candle type filters, are preferably firstly pre-coated with filter aid to provide a suitable filtration medium. The process slurry 48 is then fed to the filters. A filtrate 52 flows to an interchange heat exchanger for cooling (not shown), then on to an ion exchange feed tank (not shown). Solids 54 can be further washed to recover residual lithium contained or can be dumped directly into a suitable container 56 for off-site disposal.

[0054] Target divalent impurity levels post-the impurity precipitation step 42 and the filters 50 are, for example, magnesium less than about 1 mg/L and calcium less than about 20 mg/L.

[0055] In one embodiment, the brine is subjected to a silicon removal step (not shown) prior to the first ion exchange step. Preferably, the silicon removal step is conducted following the precipitation step 42, though it is envisaged that it may be conducted prior to the slurry 48 resulting from precipitation step 42 is treated in the silicon removal step prior to the precipitation step 42. The silicon removal step preferably targets a silicon concentration in the brine of less than about 1 mg/L (at a Li concentration of about 52,500 mg/L). Any suitable means for reducing silicon known in the art may be used. In one embodiment, the brine may be treated in an ion exchange step to remove silicon.

[0056] The filtrate 52 will likely contain residual divalent impurities, such as calcium, magnesium and strontium. The filtrate 52 is passed to a first ion exchange step 58 to substantially remove remaining divalent impurities. The removal of these divalent impurities is understood to avoid, or at least reduce, the formation of scale in electrolysis cells employed in an electrolysis step to be described hereinafter. First ion exchange step 58 preferably comprises contact of the filtrate 52 with a suitable ion-exchange resin for extracting divalent cations.

[0057] In the first ion exchange step 58, for example, three ion exchange columns are configured in series. During a loading cycle, feed solution is pumped through the columns and onto the next stage. Once a column is fully loaded, it is rinsed with water, then stripped with hydrochloric acid 34. After stripping the resin is regenerated with lithium hydroxide solution 44 or alternatively, sodium hydroxide solution. The resin employed in step 58 is selected for optimised hardness removal. In addition to the adsorption of calcium, the resin employed may also adsorb strontium, magnesium, manganese and a number of other metals. The process stages of step 58 and the associated reactions are set out in Table 1 below. It is to be understood that (r) refers to the resin phase, while “R” represents the organic functional group in the IX resin.

Table 1 : IX Process Stages

[0058] The effluent solution 53, containing for example magnesium at less than about 0.001 mg/L and calcium at less than about 0.003 mg/L, from the first ion exchange step 58 is passed to a second ion exchange step 60 to remove residual boron impurities that have passed through the precipitation step 42 and the first ion exchange step 58. Second ion exchange step 60 preferably comprises contact of the filtrate 52 with a suitable ion-exchange resin for extracting boron. In the second ion exchange step 60, during the loading cycle, feed solution is pumped through the columns and onto the next stage. Once a column is fully loaded, it is rinsed with water, then stripped with hydrochloric acid. After stripping the resin is regenerated with lithium hydroxide solution 44 or alternatively sodium hydroxide solution.

[0059] The overall cycle in the second ion exchange step 60 is similar to that of the first ion exchange step 58. However, the chemistry is different. The second ion exchange step 60 uses an anion exchange resin for boron removal. The process stages of the second ion exchange step 60 are set out in Table 2 below, together with the associated reactions. Again, it is to be understood that (r) refers to the resin phase, while “R” represents the organic functional group in the IX resin.

Table 2: IX Process Stages

[0060] Spent regeneration solution from the first ion exchange step 58 and the second ion exchange step 60 are combined and returned upstream, whereby the lithium hydroxide is used for impurity precipitation. Strip solution 62 from both the first ion exchange step 58 and the second ion exchange step 60 contains impurities and is forwarded to a wastewater treatment plant to be described hereinafter, as is the rinse water employed.

[0061 ] A product 64 from the second ion exchange step 60, for example having a boron content of less than about 0.06 mg/L, is passed to a second sulfate removal step. In the embodiment shown in Figure 1 the second sulfate removal step comprises a nanofiltration step 66 in which the solution is passed through a membrane filter. Membrane pore sizes employed are in the range of 0.1 - 100 nm, allowing high rejection of multivalent ions, including sulphate. The nanofiltration step 66 controls sulphate levels in the feed to an electrolysis step to be described hereinafter. The target levels of sulphate remaining after the nanofiltration step 66 are, for example, less than about 189 mg/L. Sulphate cannot pass through the electrolysis membrane employed, resulting in a buildup of sulphates and other impurities in the anolyte 70. To alleviate the build-up of impurities a purge of anolyte 70 to upstream of the nanofiltration step 66, for example to the first sulfate removal step 16, may be employed.

[0062] It is understood by the Applicants that for good long-term performance of nanofiltration membranes employed in the nanofiltration step 66, the product 64 is preferably cooled and preferably has the pH adjusted by hydrochloric acid to be roughly neutral. The adjusted brine is stored in the nanofiltration feed tank and pumped at high pressure to the NF filtration housings. The brine is separated into a sulphate-lean permeate and a sulphate-rich retentate. The permeate continues forward to a brine evaporator 68, while the retentate 22 is returned upstream to the first sulphate removal step 16, as noted hereinabove.

[0063] To achieve high sulphate concentration in the retentate 22, and thus reduce the volume recycled, multiple stages of nanofiltration in series, for example, are provided in the nanofiltration step 66. As the concentration increases, dilution water may be applied to avoid crystallisation. High purity water (demineralised or clean condensate) is required.

[0064] Through the impurity removal stages, the brine becomes diluted due to addition of reagents. In particular, the 32% hydrochloric acid 34 adds a significant volume of water. For efficient electrolysis, the feed concentration is increased by evaporating the excess water in the brine evaporator 68.

[0065] The brine evaporator 68, for example, includes a double effect, falling film evaporator utilising direct steam, with a final surface condenser. The system runs under vacuum to reduce the operating temperature. Evaporator feed liquor is first preheated, for example, in three stages of heat exchanger. The first two stages use heat from steam condensate and process condensate in plate heat exchangers. The third stage uses steam in a vertical shell and tube exchanger. Evaporation, for example, takes place in two stages or “effects”. The first effect is heated by boiler steam, while the second effect is heated by vapour generated in the first effect. In both effects, steam condenses on the shell side of a vertical heat exchanger while evaporation takes place inside the tubes as recirculating liquor falls downwards. Liquor and vapour are separated in the bottom chamber. Vapour passes to a cyclonic separator and through a demister to remove water droplets. Final vapour from the second effect is condensed using cooling water in the surface condenser. Feed liquor to each stage is pumped into the recirculating liquor stream, and product liquor is pumped from the recirculating stream. Preheated liquor is fed to the first effect, then first effect liquor is fed to the second effect, and second effect liquor goes to the ultra- pure brine storage tank ahead of electrolysis.

[0066] In some embodiments, it is envisaged that the brine specification may be such that the removal of water will result in the precipitation of sodium chloride. In such embodiments, brine evaporator 68 will include a crystallisation unit or stage as known by those skilled in the art.

[0067] A purified lithium chloride solution 72 from the brine evaporator 68 is passed to an electrolysis step 74 to produce lithium hydroxide 76. The lithium hydroxide solution 44 utilised previously in the method 10 is a stream preferably sourced from the lithium hydroxide 76 produced in the electrolysis step 74. In the electrolysis step 74, lithium chloride (the anolyte) is electrolytically split (with the aid of a membrane) to form the lithium hydroxide 76 (the catholyte) on the cathode side of the or each cell employed, and also form both chlorine 78 and hydrogen 80 gases. The chemical reactions taking place during the electrolysis step 74 are indicated below in Table 3.

Table 3: Electrolysis Reaction

[0068] The purified lithium chloride solution 72 of the brine evaporator 68 that is fed to the electrolysis step 74 ideally, for example, has low levels of boron, silica, and divalent cations, such as calcium and magnesium. The target levels of silicon in the electrolysis step 74 feed is less than about 2 ppm, for example less than about 500 ppb (at a Li concentration of about 82,000 mg/L). [0069] The purified lithium chloride solution 72 is largely a solution of lithium, sodium, potassium chloride and small amounts of sulphate. The pH is preferably about neutral. It is understood that keeping the concentration high enables water balance to be maintained and also high current efficiency. The presence of divalent impurities in electrolysis has negative impacts, including shortening of membrane life, an increase in operating voltage and a decrease in current efficiency. Silica impurities also have much the same effect.

[0070] Monovalent impurity cations, particularly sodium and potassium, behave in much the same way as lithium throughout the various impurity removal processes and during the electrolysis step 74. While there is an expectation that a portion of these cations will be removed during the various impurity removal steps, it is not essential that they be completely removed prior to the electrolysis step 74. These monovalent cations are not separated until crystallisation of a lithium hydroxide monohydrate product, to be described hereinafter.

[0071 ] The lithium hydroxide 76, or catholyte, is passed to a catholyte evaporation step 82. Catholyte concentration from the electrolysis step 74 is limited to around 5% LiOH to ensure efficient operation. This is well below the saturation level required for crystallisation. The catholyte evaporation step 82 is provided to increase the concentration to around 1 1% for feed to a crystallisation step, to be described hereinbelow.

[0072] The catholyte evaporation step 82 employs, for example, a four-stage, falling film evaporator utilising mechanical vapour recompression (MVR) direct steam, with a final surface condenser. Catholyte is first preheated in two stages of plate heat exchanger. The first stage uses heat from product liquor and the second uses heat from process condensate. Preheated feed is pumped into the first of four recirculation stages. In each stage, liquor is recirculated from one of the evaporator sump compartments, to the top of the evaporator heater where it flows down inside the tubes. Vapour condensing on the outside of the tubes causes evaporation to occur inside the tubes.

[0073] The vapour and liquid discharge to an integrated vapour separator. Vapour rises through a demister while liquor falls back to the sump. Some liquor overflows to the next stage, while the rest recirculates. Clean vapours from the demister pass to the suction of a single MVR fan where they are compressed and heated into the heater shell. Vapour condenses and collects in the condensate receiver.

[0074] A product of the evaporation step 82 is passed to a crystallisation step 84 that in turn provides a lithium hydroxide monohydrate (LHM) product 86, by way of a drying step 88.

[0075] The crystallisation step 84 employs, for example, two stages of crude crystallisation and redissolution followed by a final stage pure LHM crystalliser. Each crystallisation stage is preferably centred on a forced circulation (FC) crystalliser, comprising a vertical, cylindrical vessel, in which boiling takes place on the slurry surface. Solid crystals form as the solubility limit is exceeded. Crystal slurry is recirculated by an axial flow pump through a vertical shell and tube heat exchanger. Vapour from the crystalliser surface is passed to two mechanical vapour recompression (MVR) fans in series. The heated, compressed vapour is condensed in the shell of the heat exchanger, thereby recovering energy, and heating the recirculating slurry. Crystal slurry is drawn from the recirculation leg and pumped by way of a hydrocyclone into a centrifuge where crystals are separated from the centrate solution and washed.

[0076] Centrate from each centrifuge falls to the centrate tank where it combines with incoming stage feed solution. Crude crystals from stages 1 and 2 are redissolved in process condensate. The dissolving tanks provide process surge as they hold an inventory of solid crystals. Saturated LiOH is then filtered, for example using a pressure leaf filter or a plate and frame filter, and progresses to the next stage. Pure crystals from the third stage are conveyed to the LHM product drying step 88.

[0077] Lithium hydroxide reacts with carbon dioxide to form lithium carbonate which is an impurity in the LHM product and may cause it to not meet specification. Process solutions and solids should not be allowed to contact the atmosphere. Process equipment is generally sealed, and tanks are blanketed with CC>2-free air. Any carbonate formed should be collected by the pressure leaf filters prior to lithium hydroxide crystallisation to avoid contamination of the final product. [0078] Under the crystallisation conditions, sodium and potassium remain in solution while only lithium hydroxide crystallises as a solid. Concentrations of sodium and potassium increase because of evaporation. A purge system, for example a purge stream 90, is provided to control concentrations of these elements and ensure they do not contaminate the LHM product. Crystal-free mother liquor is preferably extracted from a dedicated liquor separator in each crystallisation stage and passed upstream. In this way pure crystalliser purge goes to stage 2 centrate tank, and stage 2 purge goes to stage 1 centrate tank. Stage 1 purge carries all sodium and potassium out of the LHM circuit to a lithium carbonate recovery circuit to be described hereinafter.

[0079] The purge stream 90 also serves to control chloride levels which would otherwise build up as a result of membrane slippage in electrolysis.

[0080] The drying step 88, for example, employs a closed loop shaking fluid dryer/cooler system utilising recirculating CO2 free air as the fluidising and drying gas. The bed temperature and inlet air temperature are controlled to prevent decomposition and loss of water of crystallisation. Clean CO2 free air is recirculated by way of a centrifugal fan through a series of steam air heaters and returned to the fluid bed dryer inlet wind box. Dry product is discharged from the fluid bed dryer by way of a double flap valve to provide an airlock. The gas purge from the dryer is routed to the vent scrubber system. Dryer off-gas is cleaned and cooled by way of two stages of scrubbing. The first stage comprises of a spray scrubber where the gas is quenched and cooled to condense excess moisture and for gas cleaning. A second packed bed condensing stage is used for further gas cleaning and condensing, where fresh makeup water is introduced to provide clean scrub liquor.

[0081 ] The lithium hydroxide monohydrate product 86 is packaged under conditions in which the bin, conveyor and bagging systems employed, for example, are blanketed with dry, CC -free air.

[0082] The purge 90 from the crystallisation step 84 is passed to a lithium carbonate recovery, or carbonation, step 92. The purge 90 from the LHM crystallisers is a concentrated hot solution of lithium, sodium, and potassium hydroxide. The solution is stored in an agitated feed tank. Blanketing with CO2-free air is not required from this point on. [0083] The feed liquor is pumped under flow control to two batch crystallising reactors where lithium carbonate is precipitated through the addition of CO2 94. The draft tube reactor design enables low levels of supersaturation to be maintained to provide good conditions for crystal growth. The reactors operate, for example in continuous operation or as a batch process with an 8-hour operating cycle to allow time for precipitation, discharge, cleaning, preparation, and so on. The CO2 94 is introduced at the bottom draft tube outlet to ensure rapid dispersion of gas.

[0084] After precipitation, the resulting lithium carbonate slurry is discharged batchwise by gravity into the lithium carbonate centrifuge feed tank. Preferably a batch operated peeler centrifuge is used to dewater and wash the lithium carbonate. Washing is required mainly to remove chlorides and the product thereof is fed to a wastewater treatment step 98 that in turn feeds a brine disposal step 100. The wastewater treatment step 98 also receives the strip solution 62 and entrained impurities from the ion exchange steps 58 and 60, described above.

[0085] The vent gas from the lithium carbonate recovery section is routed via a dedicated vent fan to the main LHM vent scrubber.

[0086] A drying device 95, for example a co-current rotary dryer, tunnel kiln, or other dryers known in the art, a is fed from the centrifuge. Air is heated in two stages; the first using steam and the second electrically heated. Hot air passes with the solids from the feed end towards the discharge. Exhaust gas is filtered in a dry filtration system to recover solids and produce a clean gas for discharge.

[0087] Hot, dry solids are discharged by way of a rotary valve into a lump screen. A product cooling conveyor uses cooling water to cool the final product 96 prior to packaging.

[0088] The method of the present invention may be better understood with reference to the following non-limiting examples.

Example 1 - Brine Analysis

[0089] A sample of a lithium containing brine obtained from Argentina was subjected to a chemical analysis and the are presented in 5. Table 4: Lithium Chloride Brine Assays

[0090] It can be seen that the brine contains significant amounts of calcium, magnesium, sodium, strontium, boron and sulfur in the form of sulphate. Each of these impurities must be reduced prior to treatment in an electrolysis process.

Example 2 - First Sulfate Removal Step

[0091 ] The brine of Example 1 was subjected to a combined concentration and sulphate removal process comprising an evaporation circuit and a precipitation circuit. The evaporation circuit comprised six heated reactors arranged in series with vacuum applied to improve the evaporation rate. The evaporation temperature of each reactor was maintained above 100°C to keep the brine solution boiling. The feed rate of the brine was selected to target a 50% reduction of the water content in the brine. The discharge slurry was passed to a cooling tank and the cooled slurry was filtered to remove precipitated solids. The filtrate was then passed to the precipitation circuit in which a 10% barium chloride solution to precipitate barium sulphate (BaSCU). This circuit consisted of three 3.2 L reactors to give a retention time of 60 minutes.

[0092] Three drums of filtrate where produced in the evaporation circuit and two drums of filtrate were produced in the precipitation circuit. Analysis of these filtrates is shown in Table 5.

Table 5: Chemical Assays

[0093] The concentrated brine contained ~63 g/L Li, ~1.9 g/L Na, ~6.6 g/L B, ~6.4 g/L Ca, ~6.4 g/L K and ~16.6 g/L Mg. It was also noted that the total sulphur in solution decreased from - 280 mg/L in the feed to ~ 50 mg/L in the concentrated brine during the evaporation process, which is equivalent to ~80% sulphate removal. It is also noted that no further sulphate removal occurred after adding barium chloride to the evaporated solution. This suggests that evaporation may be used to reduce the concentration of sulphate in the brine solution without the need to add barium chloride. Without wishing to be bound by theory, it is understood that removal of sulphate in the concentration step was due to other impurities, such as calcium, being present in the brine solution at high levels. Brines with lower concentrations of impurities may require treatment with barium chloride to remove sulphates. The concentration of lithium in the brine was more than doubled by evaporation, while sodium in solution decreased by more than 90%, from ~20 g/L to ~1.5 g/L.

Example 3 - Boron Removal Stage

[0094] A test was conducted to determine whether boron can be selectively extracted from the lithium chloride brine using a solvent extraction process. The trial used 2-Ethyl-1 -hexanol (Sigma-Aldrich) as the extractant, diluted in Exxsol D80 (Exxon). The organic was prepared as an organic mixture with 50% v/o 2-Ethyl-1 - hexanol in Exxsol D80. The boron solvent extraction (BSX) circuit consisted of five extraction (E) stages, two scrubbing (B) stages, two stripping (S) stages, and one washing (W) stage. Organic and aqueous streams flowed counter-currently in all circuits. [0095] The pH values in the raffinate (E1 R) were monitored during the extraction process and are shown in Figure 2. The main elements in E1 R were analysed and the trends in concentration are shown in Figure 3. A reduction in the pH was shown to reduce the boron concentration in the raffinate below 50 mg/L.

[0096] The trial demonstrated that solvent extraction could be used to reduce ~7 g/L boron in the feed brine to <50 mg/L (more than 99.3% extraction).

Example 4 - Impurity Removal

[0097] The brine solution resulting from the BSX circuit of Example 3 was subjected to an impurity removal process to target the removal of divalent impurities, particularly calcium and magnesium. The impurity removal process comprised the addition of a 1 M lithium hydroxide solution to form calcium and magnesium hydroxide precipitates, which were separated from lithium chloride solution by settling, decantation and filtration.

[0098] The lithium hydroxide solution and brine solution were pumped into the circuit comprising a train of three 10-L reactors at ambient temperature. The stoichiometric amount of lithium hydroxide solution was added to precipitate divalent elements in the brine solution. The retention time was set at about 1 13 minutes to allow enough time for reaction.

[0099] Calcium and magnesium were removed with an efficiency of >99% by precipitation with a solution of 1 M lithium hydroxide. The calcium and magnesium levels in the brine were around 5000 mg/L and 15000 mg/L, respectively. After the precipitation process, calcium and magnesium concentration were reduced to 30 mg/L and less than 10 mg/L, respectively.

Example 5 - Silicon Removal

[00100] The brine following the impurity removal step of Example 4 still contained silicon which should preferably be removed to improve the purity of the final LiOH product. The brine was subjected to an ion exchange (IX) process to confirm that IX can be used to remove a substantial portion of the remaining silicon in the brine solution. For this test, the brine was contacted with Lanxess Bayoxide® E IN 20 resin. The laboratory test was carried out with a small IX column and results showed that the discharge from the column contained less than 0.2 mg/L of silicon.

Example 6 - Divalent Ion IX and Boron IX

[00101] The brine following the impurity removal step of Example 4 still contained impurities, such as Ca, Mg, Sr and B, which require removal to improve the purity of the final LiOH product. The brine was subjected to a two stage IX process to confirm that IX can be used to remove a substantial portion of these remaining impurities in the brine solution. In the first stage (Ca IX Circuit), the brine was contacted with Lanxess MDS TP208, a macroporous cation exchange resin with chelating iminodiacetic acid groups designed for the selective removal of alkaline earth cations. In the second stage (B IX Circuit), the effluent from the first stage was contacted with Purolite S 108, a macroporous cation exchange resin with chelating N- methylglucamine groups designed for the selective removal of boron. The trial was conducted across several batches. A chemical analysis of samples from the feed brine and the effluent from the B IX Circuit was conducted. The average results across all batches is shown in Table 6

Table 6: Average Solution Assays

[00102] It can be seen the combined Ca IX Circuit and B IX Circuit were successful in reducing the concentration of calcium, magnesium, strontium and boron in the feed brine.

Example 7 - Further Sulphate Removal

[00103] The remaining brine solution contained sulphates as an impurity. To remove these impurities, the effluent resulting from the boron IX step is passed through a nanofiltration unit designed to separate divalent anions (essentially SCU² ) away from other dissolved ions. This process was operated at ambient temperatures and slightly elevated pressures using industry standard equipment and a sulphate selective membrane. The nanofiltration unit was operated at a pressure of ~ 410-450 psi (around 30 atmospheres) and a temperature of 37 - 43 °C. The feed flow rate was ~ 3,400 L per hour with a permeate flow rate of ~ 100 L per hour.

[00104] A set of 22 samples was taken during the nanofiltration test work with each pair of samples representing the permeate and reject streams at different times (hourly) during the operation of the nanofiltration. The results of a chemical analysis of these pairs are shown in Table 7.

Table ?: Nanofiltration Results

[00105] The results showed that nanofiltration demonstrates excellent retention of sulphates, with negligible flow of sulphate through the membrane during the course of the test work. The lithium concentration was fairly consistent throughout the test and little changed between the retentate and the permeate. Some retention of sodium and potassium (and thus build-up in the retentate/feed) was observed during the test.

Example 8 - Electrolysis

[00106] A trial was undertaken to test the viability of electrolysis to convert lithium chloride in brines to lithium hydroxide. The trial was undertaken using an electrochemical cell with a DSA-CI2 anode, a stainless-steel cathode and a perfluorinated cation exchange membrane obtained from Asahi Glass (AGO S-2301 ).

[00107] ICP analysis of the feed brine (3.0 M LiCI), together with the final anolyte (2.8 M LiCI) and cathode overflow (2.5 M LiOH) are shown in Table 8. Table 8: Electrolysis Results

[00108] The results demonstrate that lithium chloride in brine solutions may be converted to lithium hydroxide using electrolysis. The feed brine used in this trial did contain a significant amount of boron. It is estimated that approximately 15% of the boron in the feed brine reported to the catholyte. As expected, the Na and K content in the feed brine has reported to the catholyte in approximate proportion to their concentrations in the feed brine. The results show that the removal of sulphates, silicon, divalent impurities and boron from the brine allowed a high purity lithium hydroxide solution to be produced using electrolysis.

[00109] As can be seen from the above description, the method of the present invention provides a method by which a brines source may be processed to provide a lithium bearing solution that is suitable for further processing by electrolysis, without the need for initial conversion of the brine to lithium carbonate and subsequent causticisation by hydrated lime. The need for a bicarbonation circuit in the production of lithium carbonate is also avoided. Specific mechanisms are adopted for the handling of impurities throughout the method, being combined in a manner that provides greatest efficacy in and for the electrolysis of that lithium bearing solution.

[00110] Modifications and variations such as would be apparent to the skilled addressee are considered to fall within the scope of the present invention.

Claims

1. A method for the processing of lithium containing brines, the method comprising the method steps of:

(i) Passing a lithium containing brine to a first sulfate removal step;

(ii) Passing a product of step (i) to a boron removal step;

(iii) Passing a product of step (ii) to an impurity removal step;

(vi) Passing a product of step (v) to a second sulfate removal step;

2. A method according to claim 1 , wherein the first sulphate removal step rejects 50% or more of the sulphates present in the lithium containing brine.

3. A method according to claim 2, wherein the first sulphate removal step rejects about 50% of the sulphates present in the lithium containing brine.

4. A method according to any of the preceding claims, wherein the first sulphate removal step comprises the precipitation of sulphate compounds.

5. A method according to claim 4, wherein the first sulfate removal step comprises the addition of precipitating agent to the lithium containing brine to precipitate sulphate compounds.

6. A method according to claim 3 or claim 4, wherein the first sulfate removal step comprises subjecting the lithium containing brine to a concentration step to precipitate sulphate compounds.

7. A method according to any of the preceding claims, wherein boron removal step (iii) comprises a boron solvent extraction step.

8. A method according to any of the preceding claims, wherein boron removal step (iii) reduces the boron concentration in the lithium containing brine solution to less than 100 mg/L.

9. A method according to any of the preceding claims, wherein boron removal step (iii) reduces the boron concentration in the lithium containing brine solution to less than 40 mg/L.

10. A method according to any of the preceding claims, wherein impurity removal step (iii) removes divalent impurities from the lithium containing brine.

1 1. A method according to any of the preceding claims, wherein impurity removal step (iii) comprises a precipitation step in which the lithium containing brine is contacted with an alkali to precipitate one or more impurities.

12. A method according to claim 11 , wherein the precipitation step will precipitate one or more impurities as hydroxides.

13. A method according to claim 11 or claim 12, wherein impurity removal step (iii) comprises a precipitation step in which the lithium containing brine is contacted with lithium hydroxide to precipitate one or more impurities as hydroxides.

14. A method according to any of the preceding claims, wherein the first ion exchange step (iv) removes divalent impurities selected from the group of calcium, magnesium, manganese, strontium, and barium.

15. A method according to any of the preceding claims, wherein the second sulfate removal step (vi) utilises nanofiltration.

16. A method according to any of the preceding claims, wherein the crystallisation step (viii) comprises separation of the lithium hydroxide monohydrate product from a spent liquor.

17. A method according to claim 13, wherein the present invention further comprises passing the spent liquor from the lithium hydroxide monohydrate crystallisation step (viii) to a carbonation step (ix) in which the spent liquor is reacted with carbon dioxide to precipitate lithium carbonate.

18. A method according to any of the preceding claims, wherein the lithium containing brine is passed to a silicon removal step prior to the first ion exchange step (iii).

19. A method according to claim 15, wherein the product of step (ii) is passed to the silicon removal step prior to the first ion exchange step (iii).