A process for producing a lithium salt

Abstract

A process (10) for producing a lithium salt (190) comprising treating a plurality of lithium containing feedstocks (11,12) in an integrated plant to produce at least one selected lithium salt (190). The plurality of lithium containing feedstocks (11,12) comprises a first feedstock (11) being a lithium salt at a first grade and a second feedstock (12) being a lithium salt at a second grade, said first grade being lower than said second grade.

Description

[0001] A Process for Producing a Lithium Salt

[0002] TECHNICAL FIELD

[0003] The present invention relates to a process for producing a lithium salt.

[0004] BACKGROUND ART

[0005] The following discussion of the background art is intended to facilitate an understanding of the present invention only. The 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.

[0006] Lithium salts - in particular lithium hydroxide, lithium carbonate, lithium chloride and lithium phosphate - are currently in high demand for production of batteries to be used for electrical vehicles and other applications.

[0007] Lithium may be extracted from its ores by a range of hydrometallurgical processes to produce lithium salts. For example, lithium may be leached from a calcined material and, following a sequence of process steps, a crude lithium salt is produced. Alternatively, lithium may be extracted from a brine after evaporation and, following a sequence of process steps, a crude or pure lithium salt is produced.

[0008] There is a wide range of lithium resources available. Ores and concentrates form a major resource. However, there are other resources, for example lithium may be recovered from brines, or materials produced during treatment of lithium battery materials or during lithium battery recycling. Some of these resources may contain low levels of lithium. Lithium extraction plants, which are specifically tailored to such resources, are generally considered complex and therefore expensive in capital terms. Lithium extraction plants also occupy space which may be limited in some locations, particularly in locations of battery recycling plants.

[0009] It is against this background that the process of the present invention has been developed. SUMMARY OF INVENTION

[0010] The present invention provides, in one aspect, a process for producing a lithium salt comprising treating a plurality of lithium containing feedstocks to produce at least one selected lithium salt.

[0011] Lithium containing feedstocks may be selected from a range of lithium containing material sources, whether in solid or solution form. Thus, the process advantageously allows treatment of lithium containing materials, for example, lithium salts from brine extraction, from waste battery recycling or leaching of a lithium ore, lithium containing residue or concentrate. Each lithium salt feedstock - some of which may be in too low a volume to otherwise justify lithium recovery - may contain a different lithium salt, a different form (e.g. solid or liquid) of the same lithium salt and / or a different grade of the same lithium salt, for example different grades of lithium carbonate. This provides a single integrated plant with capacity to treat lithium containing materials from a range of sources, thus reducing space requirements for lithium plants, such space being scarce in some locations. Where a first lithium salt feedstock is in too low a volume to justify dedicated extraction, the process may enable economic recovery by bulking the first lithium salt feedstock with further lithium salt feedstock(s).

[0012] The process may produce a plurality of selected lithium salts, preferably at battery grade. Thus, for example, lithium hydroxide monohydrate (LHM) and lithium carbonate could be produced by the process at a single plant and / or at a single site. The balance between each of the battery grade lithium salts may be selected by a lithium producer as desired, for example according to economic demand for each, desirably battery grade, lithium salt.

[0013] Accordingly, the process may comprise a first group of process steps for producing a first lithium salt and a second group of process steps for producing a second lithium salt. The first and second lithium salts are then conveniently produced in controlled proportion according to economic demand. For example, lithium carbonate may be the first lithium salt produced by a first group of process steps, optionally comprising bicarbonation, purification and carbonation. In the same example, LHM may be the second lithium salt produced, advantageously in the same plant, by a second group of process steps, optionally comprising liming, purification and LHM crystallisation. Other lithium salts could be produced dependent on demand.

[0014] Lithium containing feedstocks or lithium salts produced according to the described process may be selected, without limitation, from the group consisting of lithium chloride, lithium sulphate, lithium carbonate, lithium hydroxide, lithium phosphate, lithium nitrate, lithium acetate, lithium chlorate, lithium formate, lithium hydrogen phosphite, lithium dihydrogen phosphate, lithium oxalate, lithium perchlorate, lithium tartrate and lithium thiocyanate. The number of lithium salts provided to embodiments of the process described herein may be selected by the processor and may be one or more. The selected lithium containing feedstock may, in embodiments, contain a lithium salt selected from the group consisting of industrial grade, technical grade and battery grade lithium salts. A plurality of lithium salts may be present in the feedstock.

[0015] The lithium salt may, particularly in the case of lithium salts derived from battery waste treatment, contain magnetic particles which are an important impurity. Thus, the process may include a magnetic particle separation step. Conveniently, the magnetic particle removal step is conducted following the neutralisation step, for example on the lithium salt containing slurry. A plurality of magnetic particle separation steps may be conducted if desired.

[0016] In some embodiments, the process involves extracting lithium, conveniently by leaching of a lithium containing material. The lithium containing material may, for example, be a lithium containing waste battery material, a lithium ore, a lithium containing residue (such as a gypsum residue from a sulphate process for lithium extraction, e.g. from lepidolite or other lithium aluminosilicates) or lithium mineral containing concentrate.

[0017] The process conveniently includes the further steps of:

[0018] (a) contacting an aqueous stream containing a lithium salt and impurities with a soluble phosphate to convert the lithium salt to lithium phosphate; and

[0019] (b) precipitating lithium phosphate from step (a). as part of a lithium purification process as described in the Applicant’s co-pending Provisional Application, filed 15 August 2023 under docket 298875 and the contents of which are hereby incorporated herein by reference.

[0020] Such lithium salts may be derived from minerals including spodumene, lepidolite, zinnwaldite, petalite, jadarite and amblygonite; or from the treatment of lithium containing brines. Other preferred embodiments of the invention include purification of lithium salts containing lithium recovered by treatment of used battery materials and including black mass. Lithium salts produced from lithium minerals including lithium bearing micas and clays, brines (whether salar, geothermal or oil-field), lacustrine and battery resources may be treated in the same overall process and plant.

[0021] In another embodiment, there is provided a plant for producing a lithium salt by processes as described above.

[0022] The process allows for a plurality of lithium salt containing feedstocks to be treated in a single process, ideally at a single site comprising an integrated plant, providing production flexibility in terms of feedstocks to be treated. Such a process or plant need not be tied to a single lithium resource and may be configured to produce different lithium salts, for example lithium hydroxide monohydrate and lithium carbonate, in a grade and proportion driven by economic demand. The process can also advantageously be used in conjunction with treatment of battery waste for recovery of lithium and other elements.

[0023] BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Further features of the process for extracting a lithium salt of the present invention are more fully described in the following description of several non-limiting embodiments thereof. This description is included solely for the purposes of exemplifying the present invention. It should not be understood as a restriction on the broad summary, disclosure or description of the invention as set out above. The description will be made with reference to the accompanying drawings in which:

[0025] Figure 1 is a flowsheet for a process for producing a lithium salt according to one embodiment of the present invention. Figure 2 is a flowsheet for recovering lithium from bleed streams from the process of Figure 1 and other lithium containing feedstocks.

[0026] DESCRIPTION OF PREFERRED EMBODIMENTS

[0027] Lithium Production Process

[0028] Referring to Figure 1 , there is shown a process 10 for producing a lithium salt 190. A battery grade lithium salt is suitable for applications such as electric vehicle battery production.

[0029] In the embodiment shown, process 10 consists of three blocks, namely the carbonate purification block (carbonate circuit) 20, the carbonate to hydroxide conversion block (hydroxide circuit) 30 and the lithium recovery / bleed treatment block (lithium recovery circuit) 100. The process 10 may, in other embodiments, be configured in different ways.

[0030] Feed to process 10 is 1 ) lithium carbonate 11 at a first grade; and 2) lithium carbonate 12 at a second grade. The first grade is, in embodiments, lower than the second grade. Typically, neither the first grade nor the second grade are battery grade.

[0031] Lithium carbonate 11 and lithium carbonate 12 are respectively directed to the carbonate circuit 20 and the hydroxide circuit 30. In each case, lithium carbonate 11 and 12 are mixed in tank(s) of feed preparation stage 15 with an aqueous phase to produce a slurry 16 of lithium carbonate at a pumpable solids density. Pumpable solid density may cover a wide range of solid density as appreciated by persons skilled in the art. Pumpable solids density is also dependent on the selection of the pump. The aqueous phase may be selected from any available water produced within process 10 including, for example, condensate, recirculating bicarbonation liquor, demineralised (or purified) water, or a bleed from hydroxide circuit 30.

[0032] Lithium carbonate feed for process 10 is directed to either the carbonate circuit 20 or hydroxide circuit 30 depending on the required final product or the amount and nature of impurities present in lithium carbonate feedstock 11 and 12, if lithium hydroxide monohydrate (LHM) is the required product. Lower grade feedstock 11 deports to the carbonate circuit 20 and higher grade feedstock 12 deports to the hydroxide circuit 30, if LHM is the required product. This selection also applies to lithium carbonate produced from the lithium recovery circuit 40. Additionally, if battery grade lithium carbonate is the desired end product, then the lithium carbonate feedstock is only presented to the carbonate circuit 20.

[0033] Carbonate Circuit 20

[0034] In bicarbonation stage 21 , lithium carbonate slurry 16b from the feed preparation stage 15 is first diluted to a slurry having a solids density correlated with a desired lithium concentration, for example at least 8 g / L Li when the lithium carbonate solids are completely solubilised. Dilution is with an aqueous phase which, in preferred embodiments, may be one or a mixture of purified water, recycled bicarbonation water and / or lithium carbonate wash water. Lithium hydroxide bleed solution 34a may also be added to the lithium carbonate slurry, typically on an intermittent basis.

[0035] The diluted lithium carbonate slurry is then treated with carbon dioxide gas 21a to transform carbonate ions to bicarbonate ions to optimise lithium solubilisation. Carbon dioxide 21a is sourced from reagent storage 60 and, as stream 21 aa, from decarbonation stage 24. In preferred embodiments, the carbon dioxide gas for bicarbonation is introduced under a pressure of 5-15 bar to enhance the kinetics of the bicarbonation reaction and reduce residence time. In alternative embodiments, the carbon dioxide is introduced under ambient conditions (atmospheric pressure) with dissolution typically occurring within 2 hours.

[0036] The bicarbonation liquor 21 b is then passed through a polishing filter 22 to remove insoluble impurities.

[0037] The polished bicarbonate stream 22b is then fed to an ion exchange stage 23. Ion exchange units within ion exchange stage 23 remove impurities such as remnant calcium, magnesium, heavy metal ions, boron and fluorine if present. Therefore, a series of independent ion exchange units, each with duty-specific resins are used to remove these impurities from the polished bicarbonate stream 22b. The ion exchange units of ion exchange stage 23 operate in lead, lag, and regeneration modes. A first set of columns is used to remove calcium, magnesium and heavy metals with a suitable ion exchange resin, for example an aminophosphonic chelating resin such as Purolite MTS 9500 operating at a flowrate of, for example, 8-15 bed volumes per hour.

[0038] A second set of ion exchange columns contain a suitable ion exchange resin, desirably being a borate-specific chelating resin such as Amberlite IRA 743, useful for the removal of boron. This second set of ion exchange columns may also operate at a flowrate of 8-15 bed volumes per hour.

[0039] If required, a third set of ion exchange columns is directed to removal of fluorine. This third set of ion exchange columns may also operate at a flowrate of 8-15 bed volumes per hour.

[0040] The purified lithium containing solution 23b then undergoes magnetic particle removal using inline magnetic pots containing high intensity magnets. Magnetic particles are an important impurity which can be substantially reduced through the magnetic separation treatment.

[0041] Following separation of magnetic particles, which may also be described as magnetic filtration, lithium containing solution 23b is directed to decarbonation stage 24. Here, lithium containing solution 23b is heated, preferably to higher than 90°C, to cause decarbonation of the lithium bicarbonate in solution 23b to produce purified crystallised lithium carbonate. The source of heat in one embodiment may be steam from direct steam injection if clean steam is available. Steam may be cleaned by in-process equipment or processes, or alternatively, be available from a steam generation from a source of local pure water. In alternative embodiments, lower temperatures may be used for decarbonation in combination with a manipulation of the pressure in the tank or tanks in this stage. In one embodiment, pressure manipulation may be achieved by the use of vacuum pumps. The carbon dioxide 21 aa generated by the decarbonation reaction may then be captured, optionally compressed, and advantageously re-used in bicarbonation stage 21 .

[0042] The lithium carbonate within slurry 24b is recovered in solid / liquid separation stage 25, conveniently by filtration, which in one embodiment may comprise thickening before centrifuging. In an alternative embodiment, to obtain a solids density suitable for filtration (for example, 10 wt% solids or more), limited evaporation may be carried out in decarbonation stage 24. Alternatively, solids density may be increased to 10 wt% or more by thickening in a thickener. Once a solids density suitable for filtration is obtained, the slurry 24b is filtered with the aqueous phase 25a, containing all clarified aqueous phases, being recycled to bicarbonation stage 21 .

[0043] Lithium carbonate crystals are washed, preferably with hot purified water of temperature higher than 80 °C, to displace entrained impurities and soluble lithium. Where a thickener is used, the thickener overflow is recycled to the bicarbonation stage 21 and the underflow washed, preferably with purified water. The extent of the lithium carbonate wash may vary from 0.5 times the weight of the crystals to 7 times the weight of the crystals. Washate is recycled to bicarbonation stage 21 .

[0044] In the embodiment shown, the washed lithium carbonate 90 is battery grade. Lithium carbonate 90 is directed to final product stage 35 where it is dried and subjected to magnetic particle removal using solid stream high intensity magnets in a second magnetic separation step. Then, the lithium carbonate is optionally micronised, and then packed for shipping and exported as lithium carbonate 90A.

[0045] In an alternative embodiment, a very pure - higher than battery grade - lithium carbonate is required. In this embodiment, the lithium carbonate 90 is reprocessed in a second and separate carbonate circuit (not shown) conducted as above though the magnetic particle separation step(s) may be omitted because magnetic particles have previously been separated as described above.

[0046] In a further alternative embodiment, lithium hydroxide monohydrate (LHM) may be the target product in which case lithium carbonate 80 - which may be in the form of a filter cake produced in solid / liquid separation stage 25 - is directed to the hydroxide circuit 30.

[0047] A portion of the filtrate, or thickener overflow, is - in preferred embodiments - directed to the lithium recovery circuit 100 as an impurity bleed stream. This impurity bleed stream may be combined with an impurity bleed stream 34a from crystallisation stage 34. The portion directed as bleed is determined by the maximum permissible accumulation of soluble impurities in the circulating process solution and by water balance. Hydroxide Circuit 30

[0048] Lithium carbonate may be directed to hydroxide circuit 30 as a slurry 16a from feed preparation stage 15. Hydroxide circuit 30 may also receive - as shown - lithium carbonate filter cake 80 or a lithium carbonate slurry, for example the slurry 24b.

[0049] The lithium carbonate feed(s) to hydroxide circuit 30 - and including streams 16a and 80 - are treated with hydrated lime, preferably in excess, preferably at a temperature higher than 90°C in liming stage 31. Preferably, hydrated lime 31a is added in stoichiometric excess of at least 2.5% to produce limestone in addition to aqueous lithium hydroxide. The hydrated lime 31a - produced from lime 62 in reagent preparation and storage block 60 - is preferably of high purity having low levels of silica, potassium, zinc, chloride etc. - known impurities of LHM. The residence time for the liming reaction to produce a slurry 31 b containing limestone and an aqueous phase of acceptable lithium hydroxide concentration may be about 1 hour.

[0050] The resulting lithium hydroxide slurry 31 b is directed to solid / liquid separation stage 32 for recovery of the solid limestone, conveniently by filtration. Filtration stage 32 is preferably carried out using a plate and frame filter or, alternatively, a combination of a thickener and a belt vacuum filter, or centrifuge, to separate the limestone 32a from the aqueous lithium containing phase 32b. Limestone 32a is washed to recover soluble lithium. Washing is preferably conducted counter-current and a plurality, for example, two washing stages are preferred. Washing may be conducted using process water, purified water or acidified water such as carbonated water. The obtained limestone cake may additionally be repulped in process water, purified water or carbonated water under ambient pressure conditions, that may practically range from 1.5 bar to 10 bar under a carbon dioxide atmosphere, before conducting additional slurry filtration. Filtrate may be added to a washate tank. Washate is not combined with lithium containing phase 32b but is recycled to a lime preparation (or slaking unit) in reagent preparation and storage block 60.

[0051] Following washing, limestone 32a may be directed to calcination stage 55 where it is calcined - typically at a temperature higher than 890°C - to form lime 61 and carbon dioxide 57. In one embodiment, pre-treatment of the limestone may be utilised to produce pellets, with or without drying, to obtain a free-flowing solid. Lime 61 is directed to the lime slaking unit in reagent preparation and storage block 60. An advantage of regeneration of lime from filtered limestone 32a is the return of entrained lithium in the limestone to the slaking unit and thus the hydroxide circuit 30. Build up of lime-derived impurities in downstream stages 33-35 of hydroxide circuit 30 is also prevented. Such build-up would be problematic in the event that fresh lime, containing typical impurities, continuously entered the hydroxide circuit 30. Scaling of equipment with lime-derived impurities, including silica, is also substantially reduced.

[0052] Filtrate 32b from the solid / liquid separation stage 32 (and liming stage 31 ) contains some cationic impurities (mainly calcium) because of reagent contamination. The embodiment shown includes an ion exchange stage 33 to remove these impurities. It will be understood that impurities are likely to vary with the feed materials and ion exchange - and impurity removal steps generally - may be adapted to impurities as actually present in filtrate 32b. The ion exchange stage 33 operates in lead, lag and regeneration modes using an aminophosphonic chelating resin such as Purolite MTS9500. Other ion exchange resins suitable for impurity removal may be selected. The column(s) of ion exchange stage 33 operate at a flowrate, for example up to 12 bed volumes per hour, to produce a polished aqueous lithium hydroxide stream 33b.

[0053] Lithium hydroxide stream 33b, purified by ion exchange, is then concentrated - in this embodiment - by evaporation. Evaporation is followed by magnetic particle separation, for example using inline magnetic pots containing high intensity magnets. Crystallisation 34 of LHM follows.

[0054] In this embodiment, crystallisation stage 34 involves evaporative crystallisation at suitable temperature to promote economic crystallisation, for example at temperatures ranging from 40°C to 85°C, under vacuum. The residence time of the crystallisation can range from 30 to about 180 minutes, with 60 minutes preferred. Such crystalliser practice is known to those skilled in the art of LHM production.

[0055] The crystallisation stage 34 may comprise a single crystalliser to produce battery grade LHM. However, depending on the upstream processing efficiency - in terms of impurity removal - and desired LHM product purity up to three crystallisers operating in sequence may be required. An impurity bleed 34a is desirably drawn from the crystallisers and transferred to bicarbonation stage 21 or, alternatively, to the lithium recovery circuit 100 as described below. Similarly, condensates from evaporation stages and crystallisers may also be directed to the bicarbonation stage 21. Some of the condensate may be diverted to a wash of the lithium hydroxide crystals when separated from LHM slurry 34b in solid / liquid separation stage 36.

[0056] Descaling, in particular of heat exchangers and crystallisers, is preferably conducted using cleaning-in-place (CIP) equipment. To enable a substantial degree of automation, incorporation of CIP units allow effective removal of scaling, especially silicon scaling. A CIP cleaning cycle is desirably triggered when feed temperature to the lithium hydroxide crystallisation stage 34 is below operational parameters indicating an energy transfer disruption in the heat exchangers which enable evaporative crystallisation.

[0057] Solid / liquid separation stage 36 conveniently involves centrifugal separation with the filtrate 36b being directed to the liming stage 31 , lime slaking unit or other upstream processing units.

[0058] The separated LHM crystals 36b are washed, desirably with purified water, in a wash ratio ranging from about 0.3 to 4 times of the weight of the LHM crystals 36b with a ratio of between 1 and 2 being preferred.

[0059] Carbonate is an undesirable impurity in the final LHM product 36b. However, solutions containing lithium hydroxide as well as lithium hydroxide in solid form readily adsorb carbon dioxide from contact with air. It is therefore desirable that all the process equipment used in the hydroxide circuit 30 after liming stage 31 (which forms limestone and acts as a sink of carbon dioxide) be enclosed and in contact with a carbon dioxide free atmosphere.

[0060] In the embodiment shown, the washed LHM 36b is battery grade. LHM 36b is directed to final product stage 35A where it is dried (typically at temperature lower than 60°C) in a vacuum dryer to preserve crystal integrity. Following drying, LHM 36b is subjected to magnetic particle removal using solid stream high intensity magnets in a second magnetic separation step. Then, the LHM is packed for shipping and exported as LHM 290. Lithium Recovery Circuit 100

[0061] In the embodiment shown, a combined bleed stream 122 from process 10 may be treated for lithium recovery in lithium recovery circuit 100 as shown in Figure 2. Combined bleed stream 122 may comprise a bleed stream from crystallisation stage 34 as described above together with any further bleed stream(s) from process 10, for example

[0062] Lithium recovery circuit 100 may also be provided with a plurality of lithium salt containing feedstocks provided to block 110. That is, lithium recovery circuit 100 allows treatment of a range of lithium containing feedstocks similarly to process 10. Process 10 and lithium recovery circuit 100 are integrated allowing plant flexibility to treat a range of lithium containing feedstocks of varying volume and grade in an economic manner.

[0063] In the embodiment shown, the lithium salts are 1 ) lithium sulphate, 2) lithium chloride and 3) a mixture of lithium hydroxide and lithium carbonate. It will be understood that other lithium salts or mixtures of lithium salts could be provided to block 110. Further, lithium salt feedstocks could be made available to process 100 as aqueous solutions of selected feedstocks. For purposes of exemplification only, lithium salts may be selected from the group consisting of lithium chloride, lithium sulphate, lithium carbonate, lithium hydroxide, lithium phosphate, lithium nitrate, lithium acetate, lithium chlorate, lithium formate, lithium hydrogen phosphite, lithium dihydrogen phosphate, lithium oxalate, lithium perchlorate, lithium tartrate and lithium thiocyanate. The number of lithium salts provided to embodiments of the process described herein may be selected by the processor and may be one or more.

[0064] The solid lithium salts are provided to solids unloading and feed bin 111 and are conveniently separately batched through in the embodiment shown. That is, the lithium sulphate forms one batch, the lithium chloride forms another batch and the mixture of lithium hydroxide and lithium carbonate forms another batch. The salts are likewise dissolved in a general purpose dissolution tank 112 and directed in one embodiment, in sequence to lithium sulphate solution storage tank 115, lithium hydroxide / carbonate solution storage tank 114 and lithium chloride solution storage tank 113. Such a sequence may be selected by the operator of process 100 and need not be followed in other embodiments.

[0065] The lithium salts are dissolved in general purpose dissolution tank 112 in water or an aqueous solution 112a. The aqueous solution 112a used for dissolution may conveniently comprise process liquors such as process washates, or process waters. Such streams may be derived from around the plant in which process 100 is conducted and may themselves contain a small quantity of lithium. The amount of aqueous phase delivered to general purpose dissolution tank 112 is determined by the pumps utilised for such delivery. The amount of aqueous phase may vary, as is known to practitioners in the field. In any event process waters are added until practical dissolution of each lithium salt feedstock is achieved.

[0066] Following dissolution, the solutions are directed to solution storage tanks 113 to 115 as described above.

[0067] Solutions from each of solution storage tanks 113 to 115 may be delivered separately, or together, to line 121 for transfer to the phosphate purification block 120.

[0068] In the embodiment shown, a bleed stream 122 is combined with solutions from each of solution storage tanks 113 to 115. The bleed stream 122 is removed from an upstream lithium extraction process, for example as described in the Applicant’s co-pending International Publication No. W02024000013 incorporated herein by reference though not limited to such a lithium extraction process. Bleed stream 122 may contain, for example, 2.5 g / L lithium or less and may be saturated or close to saturated with salts such as, but not limited to, potassium sulphate or sodium sulphate.

[0069] In stage 125, for example comprising one tank, pH is adjusted to a value determined by calculating the amount of required sodium hydroxide solution 125a, considering a pH of 10.5 is required after stoichiometric phosphoric acid addition in stage 126. Liquor 125b from stage 125 is directed to stage 126 where phosphoric acid 126a from phosphoric acid storage 135 is added at solution temperatures above ambient, but preferably above 80 °C to precipitate lithium phosphate which is highly insoluble in contrast to phosphates of impurities which remain soluble and therefore separable from the lithium phosphate. The pH, in the tank(s) of stage 126, is controlled to above 10, but preferably to 10.5, through the previous addition of sodium hydroxide solution 125a. In other embodiments, phosphoric acid and sodium hydroxide could be added together to the lithium containing solution in stage 126. In further embodiments, a sodium phosphate solution may be used instead of phosphoric acid in combination with sodium hydroxide. Other alkalis could be used and potassium phosphate could be used as an alternative to sodium hydroxide.

[0070] The lithium phosphate slurry 126b is separated by solid / liquid separation stage 127. Step 127 may conveniently involve filtration, for example using filters such as candle filters or plate and frame filters. The lithium phosphate depleted filtrate 127a is fed to a zero-liquor discharge (ZLD) bleed treatment unit 240 or alternative bleed treatment system. ZLD bleed treatment unit 240 produces anhydrous salts, for sale or disposal. Condensate from the ZLD unit 240 may be recycled to the process for washing duty or for slurrying duty.

[0071] The wet lithium phosphate filter cake 127b is, as shown in Figure 2, directed to lithium phosphate storage 128 where it may be dried and / or combined with lithium phosphate solids 151 unloaded into lithium phosphate receival area 150. In alternative embodiments, the wet lithium phosphate filter cake 127b may be fed directly from solid / liquid separation stage 127 to lithium phosphate degradation stage 129.

[0072] Lithium phosphate degradation stage 129 involves treatment of lithium phosphate 127b from solid / liquid separation stage 127 or lithium phosphate storage stage 128 in tank(s) with sulphuric acid 129a. Sulphuric acid for example of concentrations ranging from 10 wt% to 98 wt% acid is added in excess, for example at a 2.5% or higher stoichiometric excess of sulphuric acid. The selection of acid concentration is determined by the subsequent required solids density of the slurry in various embodiments, Treatment with sulphuric acid is at temperatures higher than 20 °C, preferably 40 °C or higher, to produce a slurry 129b consisting of lithium sulphate, unreacted sulphuric acid and phosphoric acid. The reaction scheme is as follows: 2Li3PO4(aq) + 3H2SO4(I) 3Li2SO4(s) + 2H3PO4(I)

[0073] The total residence time in the tank(s) of lithium degradation stage 129 is more than 30 min, preferably 80 min, to complete the required process cycles, including precipitation of lithium sulphate and cooling of the slurry 129b to enable filtration.

[0074] In filtration stage 130, slurry 129b is filtered to produce a lithium sulphate filter cake 130b and a combined phosphoric acid and sulphuric acid liquor 130a. Filtration stage 130 may involve using filters such as a vacuum filter, candle filter, or plate and frame filter. The filter cake 130b may be subjected to a limited wash to displace remnant phosphoric acid and the wash may thus form part of slurry filtrate 130a.

[0075] The filtrate from the wash may be returned together with the slurry filtrate 130a to phosphoric acid storage 135. If required, make up phosphoric acid 136 is directed to phosphoric acid storage 135.

[0076] Lithium sulphate filter cake 130b from the lithium phosphate degradation stage 130 may in one embodiment be recovered as a product, dried, packed and sold. In another embodiment, filter cake 130b may be introduced into a conventional lithium extraction plant; or in another embodiment be recycled to process 120. In the preferred embodiment it is dissolved in the tank(s) of the lithium sulphate dissolution stage 131 using process waters 131a sourced from elsewhere within the plant for conducting process 100. Such process waters 131 a may include condensate, washates or bleeds.

[0077] The generated lithium sulphate solution 131 b is, advantageously, passed through a magnetic particle separation mechanism, such as in-stream magnetic pots, to remove magnetic particles.

[0078] Following magnetic particle separation, lithium sulphate solution 131 b is fed slowly to a lithium carbonate crystallisation stage 132. Lithium carbonate crystallisation stage 132 involves contacting lithium sulphate solution 131 b with soda ash (sodium carbonate) 132. In one embodiment, tank(s) of lithium carbonate crystallisation stage 132 contain a charge of dissolved soda ash at a suitable concentration to precipitate lithium carbonate, for example a concentration of about 300 g / L soda ash. The reaction produces lithium carbonate crystals as a lithium carbonate slurry 132b. The temperature of the lithium carbonate production reaction is higher than ambient and the residence time ranges from 60 min to 180 min, with 90 min being preferred. The obtained lithium carbonate slurry 132b may undergo a first or second magnetic particle separation step before being separated in lithium carbonate filtration stage 133. Filtration of lithium carbonate may involve a filter such as a centrifuge and the obtained wet cake is dried in any suitable dryer, such as a rotary dryer, and the dry lithium carbonate product 190 is packed for sale. In an alternative embodiment, lithium carbonate wet cake, or dry product 190, may be returned to process 120.

[0079] The magnetic particle separation step(s) described above enable production of battery grade lithium salts with exceptionally low levels (< 20ppb) of magnetic particles, this level of magnetic particles being substantially below a typical specification of 100ppb magnetic particles maximum.

[0080] The filtrate 133a from lithium carbonate filtration stage 133 is returned to lithium bleed storage 123 which also collects a bleed stream 123 from a lithium extraction process, for example as described in the Applicant’s co-pending International Publication No. W02024000013 incorporated herein by reference. In alternative embodiments, filtrate 133 may be returned to the lithium salt solution storage tanks 113 to 115.

[0081] Those skilled in the art will appreciate that the process for producing a lithium salt of the invention described herein is susceptible to variations and modifications other than those specifically described. The invention includes all such variation and modifications. The invention also includes all of the steps and features referred to or indicated in the specification, individually or collectively and any and all combinations or any two or more of the steps or features. In particular, the process allows recovery of lithium from a bleed stream from a lithium extraction process allowing losses inherent in previous processes to be reduced or even eliminated.

[0082] Throughout this specification, 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.

[0083] The process of the present invention described herein may include one or more range of values (e.g. temperature, time, pressure etc). A range of values will be understood to include all values within the range, including the values defining the range, and values adjacent to the range which lead to the same or substantially the same outcome as the values immediately adjacent to that value which defines the boundary to the range.

[0084] The process of the present invention is not to be limited in scope by any of the specific embodiments described herein. These embodiments are intended for the purpose of exemplification only. Functionally equivalent methods are clearly within the scope of the invention as described herein.

Claims

CLAIMS1. A process for producing a lithium salt comprising treating a plurality of lithium containing feedstocks in an integrated plant to produce at least one selected lithium salt.

2. The process of claim 1 , wherein said plurality of lithium containing feedstocks comprises a first feedstock being a lithium salt at a first grade and a second feedstock being a lithium salt at a second grade, said first grade being lower than said second grade.

3. The process of claim 1 or 2, wherein said selected produced lithium salts are battery grade.

4. The process of any one of the preceding claims, comprising producing a plurality of selected lithium salts comprising a first lithium salt and a second lithium salt in controlled proportion.

5. The process of claim 4, comprising a first group of process steps for producing said first lithium salt and a second group of process steps for producing said second lithium salt.

6. The process of claim 4 or 5, wherein said first lithium salt is lithium carbonate and said second lithium salt is lithium hydroxide monohydrate (LHM).

7. The process of claim 6, wherein lithium carbonate is produced by the first group of process steps and LHM is produced, by the second group of process steps.

8. The process of claim 7, wherein the first group of process steps comprises bicarbonation, purification and carbonation.

9. The process of claim 7 or 8, wherein the second group of process steps comprises liming, purification and LHM crystallisation.

10. The process of claim 9, wherein the second group of process steps receives lithium carbonate produced by the first group of process steps.

11. The process of claim 9 or 10, wherein liming produces limestone that is washed for recovery of lithium.

12. The process of claim 11 , wherein said limestone is washed with process water, purified water or carbonated water.

13. The process of claim 11 or 12, wherein said limestone is repulped under ambient or higher pressure conditions.

14. The process of claim 13, wherein said higher pressure is 1 .5 to 10 bar.

15. The process of claim 13 or 14, wherein said limestone is repulped under a carbon dioxide atmosphere.

16. The process of any one of claims 8 to 15, wherein said purification step comprises ion exchange.

17. The process of claim 16, wherein said purification step comprises a plurality of ion exchange steps.

18. The process of any one of the preceding claims, wherein said selected lithium salt is selected from the group consisting of lithium chloride, lithium sulphate, lithium carbonate, lithium hydroxide, lithium phosphate, lithium nitrate, lithium acetate, lithium chlorate, lithium formate, lithium hydrogen phosphite, lithium dihydrogen phosphate, lithium oxalate, lithium perchlorate, lithium tartrate and lithium thiocyanate.

19. The process of any one of the preceding claims, wherein said lithium containing feedstock is derived from a source selected from the group consisting of waste battery recycling, leaching of a lithium ore, lithium containing residue or concentrate, and brines.

20. The process of any one of the preceding claims, wherein said selected lithium containing feedstock is selected from the group consisting of lithium chloride, lithium sulphate, lithium carbonate, lithium hydroxide, lithium phosphate, lithium nitrate, lithium acetate, lithium chlorate, lithium formate, lithium hydrogen phosphite, lithium dihydrogen phosphate, lithium oxalate, lithium perchlorate, lithium tartrate and lithium thiocyanate.

21. The process of claim 20, wherein said selected lithium containing feedstock contains a lithium salt selected from the group consisting of industrial grade, technical grade and battery grade lithium salts.

22. The process of any one of the preceding claims, wherein producing said at least one selected lithium salt comprises a magnetic particle removal step to remove magnetic particles.

23. The process of claim 22, comprising a plurality of magnetic particle removal steps.

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