Recovery of lithium from brines

Abstract

The present invention refers to a method for the recovery of lithium from a lithium containing brine, the method comprising the method steps of: (i) subjecting a lithium containing brine to one or more preliminary impurity removal steps to produce an intermediate brine comprising: less than 100 mg / L boron; less than 100 mg / L calcium; less than 100 mg / L magnesium; and less than 100 mg / L strontium; (ii) subjecting the lithium containing brine or the intermediate brine to at least one silicon removal step to reduce the silicon concentration to below 10 mg / L; (iii) treating the intermediate brine in at least one ion exchange step to remove further divalent cation impurities; (iv) treating the intermediate brine in at least one ion exchange step to remove further boron impurities; and (v) passing a purified brine resulting from steps (ii) to (iv) to a lithium recovery step to produce a lithium product and a lithium-depleted brine.

Description

“Recovery of Lithium from Brines”Field of the Invention

[0001] The present invention relates to a method for the recovery of lithium from brines. More particularly, the method of the present invention is intended to treat the brine in a multistage purification process to remove impurities from lithium containing brines prior to the recovery of lithium therefrom.Background Art

[0002] 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 repulped and 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.

[0003] Lithium containing brines obtained from solar brine ponds typically contain a number of impurities. The presence of these impurities impacts the ability to recover lithium from these brines with high purity. Lithium products recovered from such brines therefore require further purification treatments. Alternatively, the brines are treated to remove the impurities ahead of lithium recovery. However, the separation of lithium from other impurities is difficult, which increases the complexity of the purification treatment required. Furthermore, the relatively low ratio of lithium to impurities in the brine makes the purification of such brines inefficient. This result in a trade off between the extent of the purification and the cost of the purification circuit. This will often result in more impurities being left in solution which impact the purity of the lithium product obtained.

[0004] In International Patent Application PCT / AU2019 / 051014(WO 2020 / 069558) the present Applicant describes a method for the processing ofbrines 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 sulphates, two ion exchange steps for divalent impurity removal and boron removal respectively, and subsequent electrolysis. While this process is suitable and does remove a substantial amount of impurities, the treatment of high volumes of brines requires multiple large ion exchange vessels. This makes it difficult to scale the process up to commercial operation.

[0005] 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.

[0006] 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.

[0007] 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.

[0008] 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 term brine should also be understood to refer to solutions that result from lithium concentration processes, such as evaporation, lithium adsorption, lithium ion exchange, lithium carbonate digestion and lithium solvent extraction. 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 lithiumcontaining brine, may include a solid product comprising a crude, or relatively impure, lithium salt, for example a lithium chloride salt.Disclosure of the Invention

[0009] In accordance with the present invention there is provided a method for the recovery of lithium from a lithium containing brine, the method comprising the method steps of:(i) subjecting a lithium containing brine to one or more preliminary impurity removal steps to produce an intermediate brine comprising: less than 100 mg / L boron; less than 100 mg / L calcium; less than 100 mg / L magnesium; and less than 100 mg / L strontium;(ii) subjecting the lithium containing brine or the intermediate brine to at least one silicon removal step to reduce the silicon concentration to below10 mg / L;(iii) treating the intermediate brine in at least one ion exchange step to remove further divalent cation impurities;(iv) treating the intermediate brine in at least one ion exchange step to remove further boron impurities; and(v) passing a purified brine resulting from steps (ii) to (iv) to a lithium recovery step to produce a lithium product and a lithium-depleted brine.

[0010] In one form of the present invention, the lithium recovery step recovers a lithium hydroxide solution. Preferably, the lithium recovery step directly converts lithium chloride in the purified brine to lithium hydroxide.

[0011] In one form of the present invention, the lithium recovery step further comprises the recovery of a solid lithium hydroxide product from the lithium hydroxide solution. In one embodiment, the solid lithium hydroxide product is lithiumhydroxide monohydrate. In one embodiment, the lithium hydroxide monohydrate has a purity of at least 99%, more preferably 99.5%. Preferably, the lithium recovery step comprises subjecting the lithium hydroxide solution to a crystallisation step to produce a solid lithium hydroxide product.

[0012] Additionally or alternatively, the lithium recovery step comprises the recovery of lithium carbonate from the lithium hydroxide solution or the solid lithium hydroxide product. In one embodiment, the lithium carbonate has a purity of at least 99%, more preferably 99.5%.

[0013] In one form of the present invention, the lithium recovery step comprises an electrolysis step to produce a lithium hydroxide solution. Preferably, the electrolysis step comprises a recirculating anolyte stream. More preferably, the electrolysis step comprises a recirculating catholyte stream.

[0014] In an alternative form of the present invention, the lithium recovery step comprises a lithium solvent extraction step to produce a lithium strip solution.Preferably, the lithium solvent extraction step comprises the contact of the purified brine with an organic solution containing a lithium extractant to extract lithium from the purified brine into a loaded organic phase and subsequently recovering a lithium strip solution from the loaded organic phase.

[0015] In one form of the present invention, the method further comprises: treating at least one of the intermediate brine or the lithium-depleted brine in a sulphate membrane filtration step to remove at least a portion of the sulphates.

[0016] Preferably, the sulphate membrane filtration step is an ultrafiltration, nanofiltration or reverse-osmosis filtration step. More preferably, the sulphate membrane filtration step is a nanofiltration step. More preferably, the sulphate membrane filtration step removes sulphate impurities to a level of less than 1 g / L.

[0017] In embodiments where the lithium recovery step comprises a lithium solvent extraction step, the intermediate brine is subjected to the sulphate membrane filtration step prior to the lithium recovery step.

[0018] In embodiments where the lithium recovery step comprises an electrolysis step, at least one of the intermediate brine or the lithium-depleted brine is subjected to the sulphate membrane filtration step. Preferably, treatment of the lithium- depleted brine comprises treatment of the recirculating anolyte stream of the electrolysis step.

[0019] In one form of the present invention, the preliminary impurity removal steps comprise at least one boron removal step. Preferably, the boron removal step is selected from a boron solvent extraction step, a boron precipitation step, a boron membrane filtration step and a boron adsorption step. In one form, the boron solvent extraction step comprises contacting the lithium containing brine with an organic extractant suitable to extract boron. In one form, the boron precipitation step comprises the addition of a suitable precipitation agent. Preferably, the precipitation agent is selected from lime or magnesium hydroxide.

[0020] In one form of the present invention, the preliminary impurity removal steps comprise at least one divalent impurity removal step. Preferably, the divalent impurity removal step is selected from a brine concentration step, a divalent precipitation step, a divalent membrane filtration step and a divalent adsorption step.

[0021] In one form of the present invention, the divalent precipitation step comprises the contact of the lithium containing brine 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 and magnesium hydroxide. Alternatively, or additionally, the divalent precipitation step comprises the contact of the lithium containing brine with a carbonate to precipitate one or more impurities. Preferably, the carbonate is selected from sodium carbonate and lithium carbonate.

[0022] Preferably, the divalent ion exchange step removes divalent impurities selected from the group comprising at least calcium, magnesium and strontium. More preferably, the divalent ion exchange step further removes additional divalent impurities. Additional divalent impurities may include one or more of manganese, barium, radium and silicon. Still preferably, the divalent ion exchange step reducesthe concentration of calcium, magnesium and strontium to less than 1 mg / L each. More preferably, the divalent ion exchange step reduces the concentration of calcium, magnesium, strontium, manganese and barium to less than 1 mg / L each. In some embodiments, the divalent ion exchange step reduces the concentration of silicon to less than 1 mg / L.

[0023] Preferably, the boron ion exchange step removes boron impurities from the lithium brine to a level of less than 10 mg / L.

[0024] In one form of the present invention, the silicon removal step is selected from one or more of a silicon precipitation step and a silicon ion exchange step. In one form, the silicon precipitation step comprises the contact of the lithium containing brine or the intermediate brine with a precipitating agent selected from a hydroxide, a carbonate and magnesium chloride. Preferably, the hydroxide is selected from the group of lithium hydroxide, sodium hydroxide, calcium hydroxide, potassium hydroxide and magnesium hydroxide. Preferably, the carbonate is selected from the group of lithium carbonate, sodium carbonate, potassium carbonate and calcium carbonate. Preferably, the silicon removal step reduces the silicon concentration to below 10 mg / L at a lithium concentration of at least 10 g / L. It is envisaged that the sulphate removal step may be one or more of the preliminary impurity removal steps.Brief Description of the Drawings

[0025] 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 flow-sheet of a method for the processing of lithium containing brines, the method being in accordance with a second embodiment of the present invention;Figure 3 is a plot of change in pH of the raffinate throughout the course of the boron solvent extraction trial; andFigure 4 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

[0026] The present invention provides a method for the recovery of lithium from a lithium containing brine, the method comprising the method steps of:(i) Subjecting a lithium containing brine to one or more preliminary impurity removal steps to produce an intermediate brine comprising: less than 100 mg / L boron; less than 100 mg / L calcium; less than 100 mg / L magnesium; and less than 100 mg / L strontium;(ii) subjecting the lithium containing brine or the intermediate brine to at least one silicon removal step to reduce the silicon concentration to below 10 mg / L;(iii) treating the intermediate brine in at least one ion exchange step to remove further divalent cation impurities;(iv) treating the intermediate brine in at least one ion exchange step to remove further boron impurities; and(v) passing a purified brine resulting from steps (ii) to (iv) to a lithium recovery step to produce a lithium product and a lithium-depleted brine.

[0027] Lithium containing brines also contain a range of other impurities. The presence of such impurities can have a negative impact on the recovery of lithium from the brines. One key concern is the co-extraction of these impurities with lithium, thereby impacting the purity of the lithium that is recovered. The other concern is the impact the impurities have on the overall efficiency of the lithium recovery. For example, the presence of impurities can lead to scaling, fouling or degradation of lithium recovery equipment. To avoid such problems, the lithium- containing brine must first be treated to remove impurities. In particular, the lithium - containing brine should be treated to remove divalent cation impurities and boronimpurities prior to lithium recovery. While several impurity removal options are available in the art, the inventors have identified that the specific use of ion exchange is required to reduce the concentration of divalent cations and boron in the brine low enough to avoid the aforementioned problems with lithium recovery. However, the inventors have identified that the treatment of brines that contain a relatively large concentration of impurities using ion exchange has several disadvantages, including loss of efficiency due to resin scaling and fouling, the need for more frequent regeneration and the reduced lifespan of the resins, the need for larger and increased number of vessels to undergo the ion exchange process, the need to facilitate a proportionately larger floor space (and likely covered structures) to incorporate the larger number of vessels and ancillary equipment, the need for more parts and servicing requirements stressed by increased mechanical maintenance demands and the need for larger reagent handling systems to service the increased load on regeneration requirements.

[0028] The inventors of the present invention have identified that the above problems may be avoided by the inclusion of one or more preliminary impurity removal steps upstream of the ion exchange steps to remove boron and divalent cation impurities. The removal of a substantial portion of the impurities in the preliminary impurity removal steps allows the ion exchange steps to be optimised to improve efficiency, while still ensuring suitable removal of impurities. A further advantage of the preliminary removal steps is that they can be tailored to account for variability of impurities present in the brine. For example, individual unit operations can be bypassed when the incoming brine contains a lower concentration of particular impurities, thereby avoiding the operating cost associated operating that unit.

[0029] 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 to a preliminary impurity removal circuit 14 (noted by the dashed box in Figure 1 ). The preliminary impurity removal circuit 14 comprises the treatment of the raw brine 12 in a series of preliminary impurity removal steps to produce an intermediate brine 16 in which:the concentration of boron is less than 100 mg / L; the concentration of calcium is less than 100 mg / L; the concentration of magnesium is less than 100 mg / L; and the concentration of strontium is less than 100 mg / L.

[0030] It is envisaged that multiple impurities can be targeted in any individual preliminary impurity removal step or that individual preliminary impurity removal steps can target specific impurities. It is further envisaged that the individual preliminary impurity steps can be tailored to the impurities contained in the particular brine being treated. For example, if a raw brine contains a concentration of a particular impurity below that required in the intermediate brine, the preliminary impurity removal circuit may not require an impurity removal step that targets that impurity. This is understood to allow for the optimisation of the preliminary impurity circuit to improve efficiency. This is also understood to allow for variability in the raw brine being treated.

[0031] The present invention is not limited to any particular order of impurity removal steps in the preliminary impurity removal steps. However, in some cases it may be preferred to conduct certain impurity removal steps earlier than others. For example, it may be beneficial to conduct impurity removal steps that target multiple impurities first as this may negate the need for subsequent impurity removal steps. Furthermore, the impact that each impurity removal steps has on the chemical properties of the brine, for example pH changes or cation / anion addition, should be considered when deciding the order of the preliminary impurity removal steps.Pre-concentration

[0032] In the embodiment shown in Figure 1 , the preliminary impurity removal circuit 14 comprises a pre-concentration step 18. The pre-concentration step 18 is utilised to increase the concentration of lithium in the raw brine and to precipitate a portion of the impurities present in the raw brine. The pre-concentration step comprises, for example, heating the raw brine to boiling temperature to remove water from the raw brine. Other concentration means known in the art may similarlybe used to concentrate the raw brine. It is envisaged that the concentration step will result in the precipitation of a portion of the divalent impurities present in the raw brine. Other impurities, such as sodium, potassium and sulphates may also precipitate in the pre-concentration step. The pre-concentration step should maximise the precipitation of impurity salts while minimising lithium losses, such as through the crystallisation of lithium salts or complexes. It is understood by the inventors that lithium losses increase with increasing lithium concentration. As such, the pre-concentration step may not be suitable for raw brines that contain relatively high concentrations of lithium.

[0033] In one embodiment, the pre-concentration step targets a lithium concentration of at least 20 g / L. In one embodiment, the pre-concentration step targets a lithium concentration of at least 30 g / L. In one embodiment, the preconcentration step targets a lithium concentration of at least 40 g / L. In one embodiment, the pre-concentration step targets a lithium concentration of at least 50 g / L. In one embodiment, the pre-concentration step targets a lithium concentration of at least 55 g / L. In one embodiment, the pre-concentration step targets a lithium concentration of at least 60 g / L. In one embodiment, the preconcentration step targets a lithium concentration of at least 65 g / L. In one embodiment, the pre-concentration step targets a lithium concentration of about 70 g / L.

[0034] In one embodiment, the pre-concentration step targets a lithium concentration of between 20 g / L and 80 g / L. In one embodiment, the preconcentration step targets a lithium concentration of between 30 g / L and 80 g / L. In one embodiment, the pre-concentration step targets a lithium concentration of between 20 g / L and 75 g / L.Preliminary Boron Removal

[0035] In embodiments where the raw brine comprises a boron concentration above that required in the intermediate brine, the preliminary impurity steps comprise one or more boron removal steps.

[0036] In one embodiment, the one or more preliminary impurity removal steps produce an intermediate brine with a boron concentration of less than 90 mg / L. In one embodiment, the one or more preliminary impurity removal steps produce an intermediate brine with a boron concentration of less than 80 mg / L. In one embodiment, the one or more preliminary impurity removal steps produce an intermediate brine with a boron concentration of less than 70 mg / L. In one embodiment, the one or more preliminary impurity removal steps produce an intermediate brine with a boron concentration of less than 60 mg / L. In one embodiment, the one or more preliminary impurity removal steps produce an intermediate brine with a boron concentration of less than 50 mg / L. In one embodiment, the one or more preliminary impurity removal steps produce an intermediate brine with a boron concentration of less than 40 mg / L.

[0037] In one embodiment, the one or more preliminary impurity removal steps produce an intermediate brine with a boron concentration between 40 mg / L and 100 mg / L. In one embodiment, the one or more preliminary impurity removal steps produce an intermediate brine with a boron concentration between 40 mg / L and 90 mg / L. In one embodiment, the one or more preliminary impurity removal steps produce an intermediate brine with a boron concentration between 40 mg / L and 80 mg / L. In one embodiment, the one or more preliminary impurity removal steps produce an intermediate brine with a boron concentration between 40 mg / L and 70 mg / L. In one embodiment, the one or more preliminary impurity removal steps produce an intermediate brine with a boron concentration between 40 mg / L and 60 mg / L. In one embodiment, the one or more preliminary impurity removal steps produce an intermediate brine with a boron concentration between 40 mg / L and 50 mg / L.

[0038] In one embodiment, the one or more preliminary impurity removal steps produce an intermediate brine with a boron concentration between 10 mg / L and 100 mg / L. In one embodiment, the one or more preliminary impurity removal steps produce an intermediate brine with a boron concentration between 10 mg / L and 90 mg / L. In one embodiment, the one or more preliminary impurity removal steps produce an intermediate brine with a boron concentration between 10 mg / L and 80 mg / L. In one embodiment, the one or more preliminary impurity removal steps produce an intermediate brine with a boron concentration between 10 mg / L and70 mg / L. In one embodiment, the one or more preliminary impurity removal steps produce an intermediate brine with a boron concentration between 10 mg / L and 60 mg / L. In one embodiment, the one or more preliminary impurity removal steps produce an intermediate brine with a boron concentration between 10 mg / L and 50 mg / L. In one embodiment, the one or more preliminary impurity removal steps produce an intermediate brine with a boron concentration between 10 mg / L and 40 mg / L.

[0039] In the embodiment shown in Figure 1 , the preliminary impurity removal circuit 14 comprises a boron solvent extraction step 20. Boron in the raw brine 12 is present as borate salts of lithium and other cations. The raw brine 12 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 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 boron solvent extraction step 20. 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] Boron solvent extraction step 20 consists, for example, of 5 extraction stages, 1 scrub stage and 2 stripping stages. An organic wash stage may also be incorporated in some embodiments. 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 22 or raffinate, progresses to the next impurity removal stage. It is envisaged that boron levels in the boron-depleted aqueous solution 22 should be less than required in the intermediate solution.

[0041] The boron-loaded organic goes to a scrub stage in which it is mixed with a suitable scrub solution, for example ~pH 1 HCI solution, to remove lithium. This scrub stage also serves to remove entrained chloride from the loaded organic. Theresulting 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 a suitable stripping agent, such as sodium hydroxide. This reacts with boric acid to form an aqueous strip solution 24 of sodium borate (borax) or sodium metaborate. Stripped organic is returned to the extraction stage, while the boron loaded aqueous strip solution 24 may be further treated to recover boron products. In the embodiment shown in Figures, the aqueous strip solution 24 is directed to a crystallisation step 26 to recover sodium borate product 28.

[0042] While the embodiment shown in Figure 1 utilises solvent extraction to remove boron impurities from the raw brine, other boron removal means known in the art may be implemented in the preliminary impurity circuit. In one embodiment, boron may be removed through the precipitation of boron containing solids. The raw brine is contacted with a suitable precipitating agent to form boron solids. For example, the raw brine may be contacted with a hydroxide such as Ca(0H)2 / lime or Mg(OH)2 to precipitate calcium borate and / or magnesium borate. It is envisaged that this could be achieved by increasing the solution pH to ~8.4 with suitable reagents. In an alternative embodiment, boron may be removed using a boron membrane filtration step in which the raw brine is passed through a membrane filter suited to the separation of boron from the raw brine. It is envisaged that the membrane filter may be a ultrafiltration, nanofiltration or reverse-osmosis membrane. Suitable membranes to reduce the boron concentration to that required in the intermediate brine are known in the art. In an alternative embodiment, boron may be removed in a boron adsorption step. The raw brine may be contacted with a boron selective adsorbent to selectively remove boron from the raw brine.

[0043] In a preferred embodiment, the preliminary impurity removal steps do not include a boron ion exchange step.Preliminary Calcium Removal

[0044] In embodiments where the raw brine comprises a calcium concentration above that required in the intermediate brine, the preliminary impurity steps comprise one or more calcium removal steps.

[0045] In one embodiment, the one or more preliminary impurity removal steps produce an intermediate brine with a calcium concentration of less than 90 mg / L. In one embodiment, the one or more preliminary impurity removal steps produce an intermediate brine with a calcium concentration of less than 80 mg / L. In one embodiment, the one or more preliminary impurity removal steps produce an intermediate brine with a calcium concentration of less than 70 mg / L. In one embodiment, the one or more preliminary impurity removal steps produce an intermediate brine with a calcium concentration of less than 60 mg / L. In one embodiment, the one or more preliminary impurity removal steps produce an intermediate brine with a calcium concentration of less than 50 mg / L. In one embodiment, the one or more preliminary impurity removal steps produce an intermediate brine with a calcium concentration of less than 40 mg / L. In one embodiment, the one or more preliminary impurity removal steps produce an intermediate brine with a calcium concentration of less than 30 mg / L. In one embodiment, the one or more preliminary impurity removal steps produce an intermediate brine with a calcium concentration of less than 20 mg / L. In one embodiment, the one or more preliminary impurity removal steps produce an intermediate brine with a calcium concentration of less than 10 mg / L.

[0046] In one embodiment, the one or more preliminary impurity removal steps produce an intermediate brine with a calcium concentration between 10 mg / L and 90 mg / / L. In one embodiment, the one or more preliminary impurity removal steps produce an intermediate brine with a calcium concentration between 10 mg / L and 80 mg / / L. In one embodiment, the one or more preliminary impurity removal steps produce an intermediate brine with a calcium concentration between 10 mg / L and 70 mg / / L. In one embodiment, the one or more preliminary impurity removal steps produce an intermediate brine with a calcium concentration between 10 mg / L and 60 mg / / L. In one embodiment, the one or more preliminary impurity removal steps produce an intermediate brine with a calcium concentration between 10 mg / L and 50 mg / / L. In one embodiment, the one or more preliminary impurity removal steps produce an intermediate brine with a calcium concentration between 10 mg / L and 40 mg / L. In one embodiment, the one or more preliminary impurity removal steps produce an intermediate brine with a calcium concentration between 10 mg / L and 30 mg / L. In one embodiment, the one or more preliminary impurity removal steps produce an intermediate brine with a calcium concentration between 10 mg / L and20 mg / L. In one embodiment, the one or more preliminary impurity removal steps produce an intermediate brine with a calcium concentration between 1 mg / L and 90 mg / ZL. In one embodiment, the one or more preliminary impurity removal steps produce an intermediate brine with a calcium concentration between 1 mg / L and 80 mg / / L. In one embodiment, the one or more preliminary impurity removal steps produce an intermediate brine with a calcium concentration between 1 mg / L and 70 mg / / L. In one embodiment, the one or more preliminary impurity removal steps produce an intermediate brine with a calcium concentration between 1 mg / L and 60 mg / / L. In one embodiment, the one or more preliminary impurity removal steps produce an intermediate brine with a calcium concentration between 1 mg / L and 50 mg / / L. In one embodiment, the one or more preliminary impurity removal steps produce an intermediate brine with a calcium concentration between 1 mg / L and 40 mg / L. In one embodiment, the one or more preliminary impurity removal steps produce an intermediate brine with a calcium concentration between 1 mg / L and 30 mg / L. In one embodiment, the one or more preliminary impurity removal steps produce an intermediate brine with a calcium concentration between 1 mg / L and 20 mg / L. In one embodiment, the one or more preliminary impurity removal steps produce an intermediate brine with a calcium concentration between 1 mg / L and 10 mg / L.Preliminary Magnesium Removal

[0047] In embodiments where the raw brine comprises a magnesium concentration above that required in the intermediate brine, the preliminary impurity steps comprise one or more magnesium removal steps.

[0048] In one embodiment, the one or more preliminary impurity removal steps produce an intermediate brine with a magnesium concentration of less than 90 mg / L. In one embodiment, the one or more preliminary impurity removal steps produce an intermediate brine with a magnesium concentration of less than 80 mg / L. In one embodiment, the one or more preliminary impurity removal steps produce an intermediate brine with a magnesium concentration of less than 70 mg / L. In one embodiment, the one or more preliminary impurity removal steps produce an intermediate brine with a magnesium concentration of less than 60 mg / L. In one embodiment, the one or more preliminary impurity removal steps produce anintermediate brine with a magnesium concentration of less than 50 mg / L. In one embodiment, the one or more preliminary impurity removal steps produce an intermediate brine with a magnesium concentration of less than 40 mg / L. In one embodiment, the one or more preliminary impurity removal steps produce an intermediate brine with a magnesium concentration of less than 30 mg / L. In one embodiment, the one or more preliminary impurity removal steps produce an intermediate brine with a magnesium concentration of less than 20 mg / L. In one embodiment, the one or more preliminary impurity removal steps produce an intermediate brine with a magnesium concentration of less than 10 mg / L.

[0049] In one embodiment, the one or more preliminary impurity removal steps produce an intermediate brine with a magnesium concentration between 10 mg / L and 90 mg / / L. In one embodiment, the one or more preliminary impurity removal steps produce an intermediate brine with a magnesium concentration between 10 mg / L and 80 mg / / L. In one embodiment, the one or more preliminary impurity removal steps produce an intermediate brine with a magnesium concentration between 10 mg / L and 70 mg / / L. In one embodiment, the one or more preliminary impurity removal steps produce an intermediate brine with a magnesium concentration between 10 mg / L and 60 mg / / L. In one embodiment, the one or more preliminary impurity removal steps produce an intermediate brine with a magnesium concentration between 10 mg / L and 50 mg / / L. In one embodiment, the one or more preliminary impurity removal steps produce an intermediate brine with a magnesium concentration between 10 mg / L and 40 mg / L. In one embodiment, the one or more preliminary impurity removal steps produce an intermediate brine with a magnesium concentration between 10 mg / L and 30 mg / L. In one embodiment, the one or more preliminary impurity removal steps produce an intermediate brine with a magnesium concentration between 10 mg / L and 20 mg / L. In one embodiment, the one or more preliminary impurity removal steps produce an intermediate brine with a magnesium concentration between 1 mg / L and 90 mg / / L. In one embodiment, the one or more preliminary impurity removal steps produce an intermediate brine with a magnesium concentration between 1 mg / L and 80 mg / / L. In one embodiment, the one or more preliminary impurity removal steps produce an intermediate brine with a magnesium concentration between 1 mg / L and 70 mg / / L. In one embodiment, the one or more preliminary impurity removal steps produce an intermediate brine with a magnesium concentration between 1 mg / L and 60 mg / / L. In one embodiment, the one or morepreliminary impurity removal steps produce an intermediate brine with a magnesium concentration between 1 mg / L and 50 mg / / L. In one embodiment, the one or more preliminary impurity removal steps produce an intermediate brine with a magnesium concentration between 1 mg / L and 40 mg / L. In one embodiment, the one or more preliminary impurity removal steps produce an intermediate brine with a magnesium concentration between 1 mg / L and 30 mg / L. In one embodiment, the one or more preliminary impurity removal steps produce an intermediate brine with a magnesium concentration between 1 mg / L and 20 mg / L. In one embodiment, the one or more preliminary impurity removal steps produce an intermediate brine with a magnesium concentration between 1 mg / L and 10 mg / L.Preliminary Strontium Removal

[0050] In embodiments where the raw brine comprises a strontium concentration above that required in the intermediate brine, the preliminary impurity steps comprise one or more strontium removal steps.

[0051] In one embodiment, the one or more preliminary impurity removal steps produce an intermediate brine with a strontium concentration of less than 90 mg / L. In one embodiment, the one or more preliminary impurity removal steps produce an intermediate brine with a strontium concentration of less than 80 mg / L. In one embodiment, the one or more preliminary impurity removal steps produce an intermediate brine with a strontium concentration of less than 70 mg / L. In one embodiment, the one or more preliminary impurity removal steps produce an intermediate brine with a strontium concentration of less than 60 mg / L. In one embodiment, the one or more preliminary impurity removal steps produce an intermediate brine with a strontium concentration of less than 50 mg / L. In one embodiment, the one or more preliminary impurity removal steps produce an intermediate brine with a strontium concentration of less than 40 mg / L. In one embodiment, the one or more preliminary impurity removal steps produce an intermediate brine with a strontium concentration of less than 30 mg / L. In one embodiment, the one or more preliminary impurity removal steps produce an intermediate brine with a strontium concentration of less than 20 mg / L. In one embodiment, the one or more preliminary impurity removal steps produce an intermediate brine with a strontium concentration of less than 10 mg / L.

[0052] In one embodiment, the one or more preliminary impurity removal steps produce an intermediate brine with a strontium concentration between 10 mg / L and 90 mg / / L. In one embodiment, the one or more preliminary impurity removal steps produce an intermediate brine with a strontium concentration between 10 mg / L and 80 mg / ZL. In one embodiment, the one or more preliminary impurity removal steps produce an intermediate brine with a strontium concentration between 10 mg / L and 70 mg / / L. In one embodiment, the one or more preliminary impurity removal steps produce an intermediate brine with a strontium concentration between 10 mg / L and 60 mg / / L. In one embodiment, the one or more preliminary impurity removal steps produce an intermediate brine with a strontium concentration between 10 mg / L and 50 mg / / L. In one embodiment, the one or more preliminary impurity removal steps produce an intermediate brine with a strontium concentration between 10 mg / L and 40 mg / L. In one embodiment, the one or more preliminary impurity removal steps produce an intermediate brine with a strontium concentration between 10 mg / L and 30 mg / L. In one embodiment, the one or more preliminary impurity removal steps produce an intermediate brine with a strontium concentration between 10 mg / L and 20 mg / L. In one embodiment, the one or more preliminary impurity removal steps produce an intermediate brine with a strontium concentration between 1 mg / L and 90 mg / / L. In one embodiment, the one or more preliminary impurity removal steps produce an intermediate brine with a strontium concentration between 1 mg / L and 80 mg / / L. In one embodiment, the one or more preliminary impurity removal steps produce an intermediate brine with a strontium concentration between 1 mg / L and 70 mg / / L. In one embodiment, the one or more preliminary impurity removal steps produce an intermediate brine with a strontium concentration between 1 mg / L and 60 mg / / L. In one embodiment, the one or more preliminary impurity removal steps produce an intermediate brine with a strontium concentration between 1 mg / L and 50 mg / / L. In one embodiment, the one or more preliminary impurity removal steps produce an intermediate brine with a strontium concentration between 1 mg / L and 40 mg / L. In one embodiment, the one or more preliminary impurity removal steps produce an intermediate brine with a strontium concentration between 1 mg / L and 30 mg / L. In one embodiment, the one or more preliminary impurity removal steps produce an intermediate brine with a strontium concentration between 1 mg / L and 20 mg / L. In one embodiment, the one or more preliminary impurity removal stepsproduce an intermediate brine with a strontium concentration between 1 mg / L and 10 mg / L.Divalent Removal Options

[0053] Brines will typically contain divalent cation impurities, particularly calcium, magnesium and strontium. The one or more impurity removal steps include at least one step to reduce the concentration of these divalent cation impurities to below that required in the intermediate brine. While separate preliminary impurity removal steps may be used to target each of these impurities, it is preferred that multiple divalent cation impurities be removed in a single step. In a preferred embodiment, at least one of the preliminary impurity steps reduces the concentration of both magnesium and calcium in the raw brine. It is further preferred, that at least one of the preliminary impurity steps reduces the concentration of each magnesium, calcium and strontium in the raw brine. Other impurities contained in the brine may also be removed during the removal of the divalent cation impurities, for example, iron, aluminium, silicon or potassium.

[0054] In the embodiment shown in Figure 1 , the boron-depleted raffinate 22 is passed to a divalent precipitation step 30 which comprises the contact of the boron- depleted raffinate 22 with at least one 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 one embodiment, the divalent precipitation step 30 is conducted in multiple stages. In a first stage, raw brine is treated increase the solution pH, preferably to >6. The use of a hydroxide, preferably lithium hydroxide is used to increase the pH. Increasing the pH will result in the precipitation of some impurities, particularly magnesium, iron, aluminium, and strontium as hydroxides. In a second stage, a carbonate, preferably sodium carbonate or lithium carbonate, is added to further raise the pH of the raw brine and precipitate calcium as calcium carbonate. It is envisaged that other carbonates, such as calcium carbonate or carbon dioxide can similarly be used in the second stage to increase the pH and precipitate impurities. In a third stage, a further hydroxide, preferably lithium hydroxide, is added to precipitate the majority of the remining magnesium as magnesium hydroxide. It is envisaged that other alkalis, such as sodium hydroxide, calcium oxide, magnesium hydroxide or calciumhydroxide can similarly be used in the third stage to precipitate magnesium. It is further envisaged that the second stage and the third stage may be conducted simultaneously.

[0055] In embodiments where lithium hydroxide and lithium carbonate are used to precipitate impurities, the precipitation reactions are understood to proceed as follows:AICI3 (aq) + 3LiOH (aq) AI(OH)3(s) + 3LiCI (aq)CaC (aq) + Li2CO3(aq) -> CaCO3(s) + 2LiCI (aq)

[0056] Precipitation is preferably conducted at elevated temperature to promote reaction kinetics. Heating is preferably achieved by passing the solution through heat exchangers in which hot filtrate and / or steam are used for heating. The heated solution passes into a train of agitated tanks where lithium hydroxide and lithium carbonate, or other suitable hydroxides / carbonates, are added to raise the pH and force the divalent metals to precipitate as hydroxide and carbonate solids. It is to be understood that the divalent precipitation step 30 may be undertaken in a single step or stage, for example by way of addition of only lithium hydroxide.

[0057] A slurry 48 resulting from divalent precipitation step 30 is passed to appropriate solid liquid separation and / or filtration devices for the separation of a filtrate 16 from the solids 32. The filters devices, for example candle type filters, are preferably firstly pre-coated with filter aid to provide a suitable filtration medium. Solids 32 can be further washed to recover residual lithium contained or can be disposed of directly.

[0058] While the embodiment shown in Figure 1 utilises precipitation to remove divalent impurities from the raw brine, other divalent removal means known in the art may be implemented in the preliminary impurity circuit. In an alternative embodiment, divalent cations may be removed using a divalent membrane filtration step in which the raw brine is passed through a membrane filter suited to the removal of divalent cations. Suitable membrane filtration methods known in the artto reduce the concentration of divalent cations to that required in the intermediate brine may be used, for example ceramic filtration, electrodialysis, ultrafiltration, nanofiltration or reverse-osmosis membrane filtration. In an alternative embodiment, divalent cations may be removed in a divalent adsorption step. The raw brine may be contacted with a divalent selective adsorbent to selectively remove divalent from the raw brine. In an alternative form of the present invention, the raw brine may be removed in a bulk ion exchange step. As would be appreciated by a person skilled in the art, certain ion exchange resins have higher impurity loading capacities but with a higher discharge concentration of impurities. It is envisaged that such resin may be used in the preliminary removal circuit to reduce the concentration of divalent impurities without suffering from the disadvantages associated with the removal of large quantities of impurities. Such an ion exchange step is differentiated from the divalent ion exchange step which utilises an ion exchange resin with a lower impurity loading capacity and a low discharge of impurities.

[0059] In a preferred embodiment, the preliminary impurity removal steps do not include a divalent ion exchange step.Silicon Removal

[0060] The solution treated in the lithium recovery step should contain less than 10 mg / L silicon. In one embodiment, the preliminary impurity removal steps will include a silicon removal step. Additionally, or alternatively, the intermediate brine is treated to remove silicon. It is envisaged that in some embodiments, silicon in the brine will be removed during the removal of other impurities in the preliminary impurity removal steps. For example, the addition of an alkali to precipitate divalent impurities will also precipitate silicon in the raw brine. In one embodiment shown in Figure 1 , the intermediate brine 16 is subjected to a silicon removal step 34. In a preferred embodiment, the silicon removal step in conducted prior to the boron ion exchange step and the divalent ion exchange step.

[0061] In one embodiment, the at least one silicon removal step reduces the silicon concentration to below 9 mg / L. In one embodiment, the at least one silicon removal step reduces the silicon concentration to below 8 mg / L. In one embodiment, the at least one silicon removal step reduces the silicon concentrationto below 7 mg / L. In one embodiment, the at least one silicon removal step reduces the silicon concentration to below 6 mg / L. In one embodiment, the at least one silicon removal step reduces the silicon concentration to below 5 mg / L. In one embodiment, the at least one silicon removal step reduces the silicon concentration to below 4 mg / L. In one embodiment, the at least one silicon removal step reduces the silicon concentration to below 3 mg / L. In one embodiment, the at least one silicon removal step reduces the silicon concentration to below 2 mg / L. In one embodiment, the at least one silicon removal step reduces the silicon concentration to below 1 mg / L. In one embodiment, the at least one silicon removal step reduces the silicon concentration to below 0.5 mg / L.

[0062] In one embodiment, the silicon removal step comprises the addition of a precipitating agent to precipitate silicon. Preferably, the precipitating agent is selected from one or more of a hydroxide, a carbonate and a chloride. In embodiments where the pH of the solution is raised during the removal of other impurities that at least a portion of the silicon in the raw brine with precipitate as silica. In an alternative embodiment, the silicon removal step comprises a silicon ion exchange step. In an alternative embodiment, the silicon removal step comprises a silicon adsorption step, using for example, alumina-silicate or Bayoxide adsorbents. Any other suitable means for reducing silicon known in the art may be used.Boron and Divalent IX

[0063] The one or more preliminary impurity removal steps will reduce the concentration of boron and divalent impurities within the raw brine. The resulting intermediate brine is further treated in at least one boron ion exchange step to further reduce the concentration of boron in the intermediate brine and at least one divalent ion exchange step to further reduce the concentration of divalent impurities in the intermediate brine. The boron ion exchange step and the divalent ion exchange step can be completed in any order. In embodiments, where the silicon removal step comprises a silicon ion exchange step, the silicon ion exchange step is preferably conducted prior to the boron ion exchange step and the divalent ion exchange step.

[0064] In one embodiment, the divalent ion exchange step reduces the calcium concentration in the intermediate brine to below 1 mg / L. In one embodiment, the divalent ion exchange step reduces the calcium concentration in the intermediate brine to below 0.8 mg / L. In one embodiment, the divalent ion exchange step reduces the calcium concentration in the intermediate brine to below 0.6 mg / L. In one embodiment, the divalent ion exchange step reduces the calcium concentration in the intermediate brine to below 0.5 mg / L. In one embodiment, the divalent ion exchange step reduces the calcium concentration in the intermediate brine to below 0.4 mg / L. In one embodiment, the divalent ion exchange step reduces the calcium concentration in the intermediate brine to below 0.3 mg / L. In one embodiment, the divalent ion exchange step reduces the calcium concentration in the intermediate brine to below 0.2 mg / L. In one embodiment, the divalent ion exchange step reduces the calcium concentration in the intermediate brine to below 0.15 mg / L.

[0065] In one embodiment, the divalent ion exchange step reduces the magnesium concentration in the intermediate brine to below 1 mg / L. In one embodiment, the divalent ion exchange step reduces the magnesium concentration in the intermediate brine to below 0.8 mg / L. In one embodiment, the divalent ion exchange step reduces the magnesium concentration in the intermediate brine to below 0.6 mg / L. In one embodiment, the divalent ion exchange step reduces the magnesium concentration in the intermediate brine to below 0.5 mg / L. In one embodiment, the divalent ion exchange step reduces the magnesium concentration in the intermediate brine to below 0.4 mg / L. In one embodiment, the divalent ion exchange step reduces the magnesium concentration in the intermediate brine to below 0.3 mg / L. In one embodiment, the divalent ion exchange step reduces the magnesium concentration in the intermediate brine to below 0.2 mg / L. In one embodiment, the divalent ion exchange step reduces the magnesium concentration in the intermediate brine to below 0.15 mg / L.

[0066] In one embodiment, the divalent ion exchange step reduces the strontium concentration in the intermediate brine to below 1 mg / L. In one embodiment, the divalent ion exchange step reduces the strontium concentration in the intermediate brine to below 0.8 mg / L. In one embodiment, the divalent ion exchange step reduces the strontium concentration in the intermediate brine to below 0.6 mg / L. In one embodiment, the divalent ion exchange step reduces the strontiumconcentration in the intermediate brine to below 0.5 mg / L. In one embodiment, the divalent ion exchange step reduces the strontium concentration in the intermediate brine to below 0.4 mg / L. In one embodiment, the divalent ion exchange step reduces the strontium concentration in the intermediate brine to below 0.3 mg / L. In one embodiment, the divalent ion exchange step reduces the strontium concentration in the intermediate brine to below 0.2 mg / L. In one embodiment, the divalent ion exchange step reduces the strontium concentration in the intermediate brine to below 0.15 mg / L.

[0067] In one embodiment, the boron ion exchange step reduces the boron concentration in the intermediate brine to below 10 mg / L. In one embodiment, the boron ion exchange step reduces the boron concentration in the intermediate brine to below 8 mg / L. In one embodiment, the boron ion exchange step reduces the boron concentration in the intermediate brine to below 6 mg / L. In one embodiment, the boron ion exchange step reduces the boron concentration in the intermediate brine to below 5 mg / L. In one embodiment, the boron ion exchange step reduces the boron concentration in the intermediate brine to below 4 mg / L. In one embodiment, the boron ion exchange step reduces the boron concentration in the intermediate brine to below 3 mg / L. In one embodiment, the boron ion exchange step reduces the boron concentration in the intermediate brine to below 2 mg / L.

[0068] In the embodiment shown in Figure 1 , the intermediate brine 36 resulting from the silicon removal step 34 is passed to divalent ion exchange step 38.Divalent ion exchange step 38 preferably comprises contact of the intermediate brine 36 with a suitable ion-exchange resin for extracting divalent cations from the intermediate brine 36. In the divalent ion exchange step 38, 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, for example. After stripping the resin is regenerated with, for example, lithium hydroxide solution or alternatively, sodium hydroxide solution. The resin employed in divalent ion exchange step 38 is selected for optimised hardness removal. Any resin available in the art that is suitable for the removal of divalent impurities from chloride solutions may be employed in divalent ion exchange step 38. Preferably, the resin is a cation exchange resin. In one embodiment, the resin is a strong acid or weak acid cationexchange resin. Preferably, the resin is a weak acid cation exchange resin. In one embodiment, the resin is a microporous resin. In one embodiment, the resin is a polymeric resin. Preferably, the resin is a polystyrenic or polyacrylic resin. In one embodiment, the resin is a chelating resin. In one embodiment, the resin is a chelating resin with chelating functional groups selected from phosphonic acid groups, amino-phosphonic acid groups, iminodiacetate groups. Suitable commercially available resins include Lanxess™ Lewatit MonoPlus™ TP 308, Purolite™ S9320, Diaion™ CR11 and DuPont™ AmberSep™ IRC747 UPS. In addition to the extraction of calcium, the resin employed may also extract strontium, barium, magnesium, manganese and a number of other metals. Example process stages of divalent ion exchange step 38 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

[0069] The effluent solution 40 from the divalent ion exchange step 38 is passed to a boron ion exchange step 42 to remove residual boron impurities. Boron ion exchange step 42 preferably comprises contact of the effluent solution 40 with a suitable ion-exchange resin for extracting boron. Divalent ion exchange step 38 and boron ion exchange step 42 are separate stages, such that the intermediate brine is contacted with at least one ion-exchange resin for extracting boron impurities and at least one ion-exchange resin for extracting divalent impurities. In the boron ion exchange step 42, 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, typically with hydrochloric acid. After stripping the resin is regenerated with lithium hydroxide solution or alternatively sodium hydroxide solution. The overall cycle in the boron ion exchange step 42 is similar to that of thedivalent ion exchange step 38. However, the chemistry is different. The boron ion exchange step 42 uses an anion exchange resin for boron removal. Any resin available in the art that is suitable for the removal of boron impurities from chloride solutions may be employed in boron ion exchange step 42. Preferably, the resin is an anion exchange resin. In one embodiment, the resin is a strong base or weak base anion exchange resin. In one embodiment, the resin is a microporous resin. In one embodiment, the resin is a polymeric resin. Preferably, the resin is a polystyrenic or polyacrylic resin. In one embodiment, the resin is a chelating resin. In one embodiment, the resin is a chelating resin with chelating functional groups selected from N-methylglucamine groups and polyhydroxy groups. Suitable commercially available resins include Lanxess™ Lewatit MonoPlus™ MK 51 , Purolite™ S108, Purolite™ NRW505, and DuPont™ AmberSep™ IRA743 UPS. Example process stages of the boron ion exchange step 42 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

[0070] Spent regeneration solution from the divalent ion exchange step 38 and the boron ion exchange step 42 are combined and returned upstream, whereby the contained lithium hydroxide can be used for impurity precipitation. Strip solutions from both the divalent ion exchange step 38 and the boron ion exchange step 42 contain impurities and can be forwarded to a wastewater treatment plant, as is the rinse water employed.Sulphate Removal

[0071] Brines typically contain sulphates as impurities which can interfere with the recovery of lithium. In particular, in embodiments where electrolysis is used to recover lithium, sulphate ions are unable to pass through the electrolysismembranes employed. This can result in a build up of sulphates in the anolyte of the electrolysis unit. This buildup of sulphates has a negative impact on the operation of the electrolysis cell. High concentrations of sulphates ultimately can impact or reduce current efficiency and voltage due to potential scaling, corrosion, conductivity imbalance and pH imbalance. While it is possible to purge sulphates in the anolyte loop, this would also result in a high loss of lithium.

[0072] In one embodiment of the present invention, the method comprises a sulphate membrane filtration step to remove sulphates. In the sulphate membrane filtration step, the solution is passed through a suitable membrane filter to reject a substantial portion of sulphate ions. Ultrafiltration membranes, nanofiltration membrane and reverse-osmosis membranes may each be used in the sulphate membrane filtration step. Membrane pore sizes employed are in the range of 0.1 - 100 nm, allowing high rejection of multivalent ions, including sulphate. It is envisaged that the raw brine may be subjected to additional sulphate removal steps prior to the sulphate membrane filtration step. As discussed above, the preconcentration of the raw brine may result in the precipitation of sulphates. Sulphate may also be precipitated from the raw brine or the intermediate brine by the addition of a suitable precipitating agent, such as barium sulphate. However, it is generally expected that the sulphate membrane filtrate step alone will be sufficient. In one embodiment, the sulphate membrane filtration step removes sulphate impurities to a level of less than 1 g / L. In one embodiment, the sulphate membrane filtration step removes sulphate impurities to a level of less than 0.8 g / L. In one embodiment, the sulphate membrane filtration step removes sulphate impurities to a level of less than 0.6 g / L. In one embodiment, the sulphate membrane filtration step removes sulphate impurities to a level of less than 0.5 g / L. In one embodiment, the sulphate membrane filtration step removes sulphate impurities to a level of less than 0.25 g / L.

[0073] In one embodiment, the intermediate brine solution is treated in the sulphate membrane filtration step prior to lithium recovery. In an alternative or additional embodiment, a lithium-depleted brine resulting from the electrolysis step is treated in the sulphate membrane filtration step. In the embodiment shown in Figure 1 , the effluent solution 44 from the boron ion exchange step 42 is treated in a nanofiltration step 46 to remove sulphates. It is envisaged that the intermediate brine solution may be subjected to the nanofiltration step 46 prior to the divalent ionexchange step 38 and / or the boron ion exchange step 42. The use of the nanofiltration step 46 prior to lithium recovery controls sulphate levels in the feed to the lithium recovery step. The target levels of sulphate remaining after the nanofiltration step 46 are, for example, less than about 500 mg / L.

[0074] Subject to the membrane selected in the nanofiltration step 66, it may be advantageous to adjust the brine pH to archive optimum and / or long term performance of the membranes. 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 48 and a sulphate-rich retentate 50. The permeate 48 continues forward to a brine evaporator 52. The retentate 50 may contain lithium values. In the embodiment shown in Figure 1 , the retentate 50 is passed to a sulphate removal step 54, prior to being recirculated to the preliminary impurity removal circuit 14. Sulphate removal step 54 preferably comprises the precipitation of calcium sulphate or barium sulphate.

[0075] To achieve high sulphate concentration in the retentate 50, and thus reduce the volume recycled, multiple stages of nanofiltration in series, for example, are provided in the nanofiltration step 46. As the concentration increases, dilution water may be applied to avoid crystallisation. High purity water (demineralised or clean condensate) is preferentially used. Alternatively, the retentate can be simply disposed.Concentration

[0076] 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. In some embodiments, it may be beneficial to increase the concentration of lithium prior to lithium recovery, particularly electrolysis. In the embodiment shown in Figure 1 , the lithium concentration in the sulphate-lean permeate 48 is increased by evaporating the excess water in the brine evaporator 52. The brine evaporator 52, for example, includes a double effect, falling film evaporator utilising direct steam, with a final surface condenser. 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 and / or potassiumchloride. Residual sulphates may also be precipitated. In such embodiments, brine evaporator 52 will include a crystallisation unit or stage as known by those skilled in the art.Lithium Recovery

[0077] The purified lithium chloride solution resulting from at least the divalent ion exchange step 38 and the boron ion exchange step 42 is passed to a lithium recovery step to recover a lithium product and produce a lithium depleted brine. Throughout the specification and claims, unless the context requires otherwise, the term “lithium-depleted brine”, will be understood to refer to a brine solution that has been treated to remove at least a portion of the lithium therefrom. It should not be understood to require that the brine contains no lithium.

[0078] In the embodiment shown in Figure 1 , the purified lithium chloride solution 56 from the brine evaporator 52 is passed to an electrolysis step 58 to produce lithium hydroxide solution 60. In the electrolysis step 58, lithium chloride (the anolyte) is electrolytical ly split (with the aid of a membrane) to form the lithium hydroxide solution 60 (the catholyte) on the cathode side of the or each cell employed, and also form both chlorine and hydrogen gases. The chemical reactions taking place during the electrolysis step 58 are indicated below in Table 3.

[0079] The purified lithium chloride solution 56 is largely a solution of lithium, sodium, potassium chloride and small amounts of sulphate. 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 operatingvoltage and a decrease in current efficiency. Silica impurities also have much the same effect. 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 58. While there is an expectation that a portion of these monovalent cations will be removed during the various impurity removal steps, it is not essential that they be completely removed prior to the electrolysis step 58. These monovalent cations are not separated until crystallisation of a lithium hydroxide monohydrate product, to be described hereinafter. The process should not be considered to require that monovalent impurities must remain. They can be removed prior to lithium recovery.Sulphates in Anolyte loop

[0080] In a preferred form of the present invention, electrolysis step 58 comprises an anolyte loop, in which a recirculating anolyte stream comprising a partially lithium- depleted brine is recirculated through the anode compartment. In this embodiment, the purified lithium chloride solution is added to the recirculating anolyte stream to replenish the lithium ions consumed in the electrolysis step 58. As discussed above, sulphate ions are rejected in the electrolysis step 58 and so the recirculation of the lithium chloride solution will lead to a buildup of sulphates in the recirculating anolyte stream. The removal of sulphates in the sulphate membrane filtration step prevents a significant buildup of sulphates. In one embodiment, the lithium-depleted brine in the recirculating anolyte stream is subjected to the sulphate membrane filtration step to remove sulphates from the recirculating anolyte stream. It is envisaged that such a membrane filtration step could be used as an alternative to the sulphate removal prior to the lithium recovery step or additionally thereto. In a preferred embodiment, the electrolysis step 58 comprises a catholyte loop, in which a recirculating catholyte stream comprising lithium hydroxide is recirculated through the cathode compartment. In this embodiment, water is added to the recirculating catholyte stream to replenish water in the electrolysis step 58 and a portion of the recirculating catholyte stream is withdrawn as lithium hydroxide solution 60.

[0081] The lithium hydroxide solution 60, or catholyte, is passed to a crystallisation step 62 to precipitate lithium hydroxide solids, preferably as lithium hydroxidemonohydrate, which is filtered from the slurry and dried to produce a solid lithium hydroxide monohydrate product 64.

[0082] The crystallisation step 62 employs, for example, one or two stages of crude crystallisation and redissolution followed by a final stage pure lithium hydroxide monohydrate (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 and optionally repulped. 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. Precipitated lithium hydroxide solids are then filtered, for example using a pressure leaf filter or a plate and frame filter, and subsequently dried.

[0083] A purge solution 65 is generated from the LHM crystalliser used in crystallisation step 62. As would be appreciated by a person skilled in the art, a crystalliser purge is a liquid stream that is withdrawn from the crystalliser to remove dissolved impurities, thereby increasing the purity of the crystallised solid products. The lithium hydroxide solution 60 primarily comprises a mixture of LiOH, KOH and NaOH, with a higher ratio of K / Na:Li than the lithium hydroxide solution 60. It is envisaged that the primary use of the purge solution will be as a reagent for pH adjustment, such as by recirculating at least a portion of the purge solution to the divalent precipitation step 30 as hydroxides required for magnesium precipitation or in any part of the circuit where pH adjustment is required. The recirculation of the purge solution 65 also recirculates lithium back into the circuit, thereby avoiding losses. It is envisaged that the purge solution will be transferred to a storage tank which will then be fed to any other required parts of the flowsheet.

[0084] In some embodiments, it is envisaged that any excess of purge solution available, can be converted back to a chloride in a separate reactor vessel by addition of hydrochloric acid, preferably regenerated from the hydrogen and chloride gas evolved in electrolysis. Figure 2 shows an embodiment of the present invention that incorporates treatment of at least a portion of the purge solution to convert it into a chloride. In this embodiment, the purge solution 102 generated in the crystallisation step 62, or at least a portion thereof, is directed to an acidification step 104, where it is contacted with hydrochloric acid 106. In the embodiment shown in Figure 2, the hydrochloric acid 106 is regenerated from the hydrogen and chloride gas evolved in electrolysis step 58, but this is not essential. Acidification step 104 coverts the hydroxides in the purge solution 102 to chlorides, thereby generating first chloride stream 108. In this embodiment, first chloride stream 108 is treated in crystallisation step 110 to crystallise potassium chloride salt 112. KCI and NaCI each have a lower solubility limit than LiCI in aqueous solutions, which can be exploited to preferentially crystallise KCI and NaCI over LiCI, thereby allowing removal of potassium and sodium ions from the first chloride solution 108. Any suitable crystalliser or concentrator known in the art may be used in crystallisation step 110. Crystallisation step 110 produces a second chloride solution 114, having a reduced potassium and sodium content than first chloride stream 108, which is recirculated back into the main circuit to recover lithium. Second chloride stream is preferably combined with intermediate brine 36, thereby allowing removal of impurities that may be present. It is envisaged that the first chloride stream 108 may be directly recirculated into the main circuit, but that this may result in a build up of potassium in the circuit up to the solubility limit of concentration step 52. The crystallisation of potassium from the purge solution 102 may be used to reduce the concentration of potassium that is recirculated through the electrolysis step 58. Lower concentrations of potassium in the feed solution treated in the electrolysis step 58 has been found to improve the overall efficiency and subsequently power demand of the electrolysis process. Lower concentrations of potassium in the feed solution treated in the electrolysis step 58 also reduces the concentration of potassium in lithium hydroxide solution 60 that is fed to the crystallisation stage 62, this lowers the relative amount of purge required to maintain acceptable purity of the lithium hydroxide.

[0085] The embodiment shown in Figure 1 also includes the possibility to generate lithium carbonate in a carbonation step 66. The primary inputs for the carbonation step 66 are a portion of the lithium hydroxide solution 68 (catholyte) produced in the electrolysis step, a portion of the purge solution 65 and / or a portion of the LHM crystals 70 which are re-dissolved. In a preferred embodiment, the feed liquor is pumped under flow control to two batch crystallising reactors where lithium carbonate is precipitated through the addition of CO2 or Na2COs. 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. When CO2 is used, it is introduced at the bottom draft tube outlet to ensure rapid dispersion of gas. After precipitation, the resulting lithium carbonate slurry is discharged batchwise by gravity into a lithium carbonate centrifuge feed tank. Preferably a batch operated peeler centrifuge is used to dewater and wash the lithium carbonate, thereby producing lithium carbonate product 72. In an alternative embodiment, the recovery step comprises the recovery of lithium as lithium carbonate. In this embodiment, the lithium hydroxide solution 60 generated in the electrolysis step is directed to the carbonation step 66 as described above to produce lithium carbonate. It is envisaged that such embodiment may be used when the recovery of lithium carbonate is preferred over lithium hydroxide.Alternative Lithium Recovery

[0086] In an alternative embodiment of the present invention, the lithium recovery step comprises a lithium solvent extraction step. It is envisaged that the use of an organic solution containing a suitable lithium extractant may be used to extract lithium from the purified brine. Alternatively, solvent extraction may be used to directly convert the lithium chloride solution to a lithium hydroxide solution. For example, a mixture of the quaternary ammonium chloride Aliquat 336 and 2,6-di-tert- butylphenol (1 :1 molar ratio) in the aliphatic diluent Shellsol D70 maybe used to replace chloride ions with hydroxide ions. In such an example, the solvent extraction process preferably involves two steps. In the first step, the organic phase is contacted with an aqueous sodium hydroxide solution. The phenol is deprotonated, and a chloride ion is simultaneously transferred to the aqueous phase, leading toin situ formation of a quaternary ammonium phenolate in the organic phase. The organic phase, comprising the quaternary ammonium phenolate, is contacted in the second step with an aqueous lithium chloride solution. This contact converts the phenolate into the corresponding phenol by protonation with water extracted to the organic phase, followed by a transfer of hydroxide ions to the aqueous phase and chloride ions to the organic phase. As a result, the aqueous lithium chloride solution is transformed into a lithium hydroxide solution.Example 1 - Brine Analysis

[0087] A sample of a lithium containing brine obtained from Argentina was subjected to a chemical analysis and are presented in Table 4.Table 4: Lithium Chloride Brine Assays

[0088] 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 - Pre-Concentration Step

[0089] The brine of Example 1 was subjected to a combined concentration and preliminary 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 evaporationtemperature 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 (BaSCM). This circuit consisted of three 3.2 L reactors to give a retention time of 60 minutes.

[0090] Three drums of filtrate were 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

[0091] 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 / LExample 3 - Boron Removal Stage

[0092] 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 as the extractant, diluted in Exxsol D80 (Exxon). The organic was prepared as an organic mixture with 50% v / v 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.

[0093] The pH values in the raffinate (E1 R) were monitored during the extraction process and are shown in Figure 3. The main elements in E1 R were analysed and the trends in concentration are shown in Figure 4. A reduction in the pH was shown to reduce the boron concentration in the raffinate below 50 mg / L.

[0094] 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 - Divalent Impurity Removal

[0095] 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.

[0096] 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 113 minutes to allow enough time for reaction.

[0097] Calcium and magnesium were removed with an efficiency of >99% by precipitation with a solution of 1 M lithium hydroxide. The calcium and magnesiumlevels 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

[0098] 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 lithium hydroxide 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

[0099] 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 lithium hydroxide 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

[0100] 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 - Sulphate Membrane Filtration

[0101] 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 SO42’) 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. Due to the low sulphate level in the feed brine, the retentate was returned into the feed brine, so that the feed sulphate concentration slowly increased with time, resulting in a corresponding increase in the retentate sulphate concentration.

[0102] 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 7: Nanofiltration Results

[0103] 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

[0104] 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 (AGC S- 2301 ).

[0105] 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

[0106] 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.Example 9 - Electrolysis

[0107] A second electrolysis trial was conducted a larger scale to test impact that lithium concentration had on the electrolysis process. A purified brine sample (600L, 5.8 M Li) was directed through a first divalent IX stage and was purified to approximately 10 M lithium, batchwise via a rotary evaporator, resulting in the crystallisation of a portion of the sodium in the brine. The brine was then re-diluted to 5.8 M lithium and passed through a further IX stage. The solution assays indicate very minor reduction of calcium and magnesium impurities were achieved, but that over half the sodium was removed. A summary of the solution assays at each stage is provided in Table 9.Table 9: Lithium Chloride Brine Solution Assays

[0108] The trial was undertaken for 1 ,000 hrs using an electrochemical cell with a DSA-CI2 anode, a stainless-steel cathode and a perfluorinated cation exchange membrane obtained from Asahi Glass (AGC S-2301 ). Starting anolyte of 3 M LiCI and the processed 5.8 M brine was fed at a constant flow to replenish the lithium concentration as it was depleted. The catholyte product solution analysis is summarised in Error! Reference source not found.. Aside from the expected sodium and potassium, there were no unusual impurities in the 2 M LiOH catholyte produced.Table 10: Lithium Hydroxide Catholyte Solution Assays

[0109] The analysis of the end solutions, membrane, and anode all indicated very stable performance during the course of the 1 ,000-h testExample 10 - Crystallisation

[0110] A sample of approximately 110 kg lithium hydroxide catholyte produced from the 1 ,000-h electrolysis campaign in Example 9 was subjected to a lithium hydroxide monohydrate (LHM) crystallisation test. The filtered feed was preconcentrated at atmospheric conditions and then charged to the crystalliser where water was further evaporated under the set process conditions (80 °C). The feed liquor was added intermittently, water was evaporated from the system in a true continuous manner and the purge liquor intermittently removed from the boiling contents of the crystalliser. After 2 hours with continuous feed addition, the remaining slurry was removed from the crystalliser. The solids which had formed (under semi-continuous conditions) were centrifuged and sampled. These solids were then repulped and sampled again. Repulping was done using a battery grade impurity level lithium hydroxide solution, which was made up and was not produced in this process. The mother liquor prior to repulping was recharged to the vessel, with the process being repeated for a total of eight crops. The averaged compositions of the Stage 1 semi-continuous results are presented in Error!Reference source not found..Table 11 : Averaged Chemical Analysis of Stage 1 Semi-continuous Samples

[0111] To conduct the second stage, the repulped solids produced in the first stage were dissolved in deionised water to just below the saturation value at 80 C(«3.8 wt. % Li) and then filtered through the colloidal cartridge filter to remove any Li2COs and other insoluble components. This ensured the Stage 2 feed to the crystalliser was clean and free of any particles. The polished filtrate was used as the feed to the crystalliser. The final solids were washed with wash water applied at a ratio of 25 g deionised water per 100 g of solids and at ambient temperature (15 °C - 20 °C). The averaged compositions of the Stage 2 semi-continuous results are presented in Table 12.Table 12: Averaged Chemical Analysis of Stage 2 Semi-continuous Samples

[0112] The LHM produced in the second stage semi-continuous crops was sufficiently pure (i.e. met the required specification) such that a third stage of crystallisation was not required. Sodium and potassium concentrations in Stage 1 solids were above the battery grade LHM specifications, as expected, which confirmed that a multi-stage process is required to achieve the desired composition. In the second stage, the removal of sodium and potassium achieved a product composition that was well within the required battery grade LHM specification. The carbonate content across the campaign was also low, demonstrating the low carbonate formation during the LHM crystallisation process.

[0113] 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.

[0114] Modifications and variations such as would be apparent to the skilled addressee are considered to fall within the scope of the present invention.

Claims

CLAIMS1 . A method for the recovery of lithium from a lithium containing brine, the method comprising the method steps of:(i) subjecting a lithium containing brine to one or more preliminary impurity removal steps to produce an intermediate brine comprising: less than 100 mg / L boron; less than 100 mg / L calcium; less than 100 mg / L magnesium; and less than 100 mg / L strontium;(ii) subjecting the lithium containing brine or the intermediate brine to at least one silicon removal step to reduce the silicon concentration to below 10 mg / L;(iii) treating the intermediate brine in at least one ion exchange step to remove further divalent cation impurities;(iv) treating the intermediate brine in at least one ion exchange step to remove further boron impurities; and(v) passing a purified brine resulting from steps (ii) to (iv) to a lithium recovery step to produce a lithium product and a lithium-depleted brine.

2. A method according to claim 1 , wherein the lithium recovery step comprises an electrolysis step to produce a lithium hydroxide solution.

3. A method according to claim 1 , wherein the lithium recovery step comprises a lithium solvent extraction step to produce a lithium strip solution.

4. A method according to any one of the preceding claims, wherein the method further comprises:treating at least one of the intermediate brine or the lithium-depleted brine in a sulphate membrane filtration step to remove at least a portion of the sulphates.

5. A method according to claim 4, wherein the sulphate membrane filtration step is an ultrafiltration, nanofiltration or reverse-osmosis filtration step.

6. A method according to claim 4 or claim 5, wherein the sulphate membrane filtration step removes sulphate impurities to a level of less than 1 g / L7. A method according to any one of the preceding claims, wherein the preliminary impurity removal steps comprise at least one pre-concentration step.

8. A method according to claim 7, wherein the pre-concentration step targets a lithium concentration of at least 20 g / L.

9. A method according to any one of the preceding claims, wherein the preliminary impurity removal steps comprise at least one boron removal step.

10. A method according to claim 9, wherein the boron removal step is selected from a boron solvent extraction step, a boron precipitation step, a boron membrane filtration step and a boron adsorption step.11 . A method according to any one of the preceding claims, wherein the preliminary impurity removal steps comprise at least one divalent impurity removal step.

12. A method according to claim 11 , wherein the divalent impurity removal step is selected from a brine concentration step, a divalent precipitation step, a divalent membrane filtration step and a divalent adsorption step.

13. A method according to any one of the preceding claims, wherein the at least one ion exchange step to remove further divalent cation impurities reduces the concentration of calcium, magnesium and strontium to less than 1 mg / L each.

14. A method according to any one of the preceding claims, wherein the at least one ion exchange step to remove further boron impurities removes boron impurities from the lithium brine to a level of less than 10 mg / L.

15. A method according to any one of the preceding claims, wherein the silicon removal step is selected from one or more of a silicon precipitation step and a silicon ion exchange step.

16. A method according to claim 15, wherein the silicon precipitation step comprises the contact of the lithium containing brine or the intermediate brine with a precipitating agent selected from a hydroxide, a carbonate and magnesium chloride.

Images