TECHNICAL FIELD

[0001] The present invention relates to a process for producing a lithium salt such as lithium carbonate and lithium hydroxide.

BACKGROUND ART

[0002] 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.

[0003] 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. Indeed, demand is currently so high that there is pressure to treat lower grade lithium resources.

[0004] Lithium may be extracted from its ores or brines containing lithium salts by a range of hydrometallurgical processes to produce lithium salts. More modern processes involve recycling of process streams, in particular the leaching reagent. Over time, impurities - such as alkali, alkaline earth, transition metals or heavy metals can build up in the recycled streams and these impurities require removal or reduction to an acceptable level to avoid disruption of the extraction process.

[0005] Lithium can - apart from its extraction from brines - be extracted from a range of minerals. Such minerals include alumino-silicates such as spodumene but lithium can also be found in economically relevant though relatively low quantities in micas and mica type minerals such as the phyllosilicate lepidolite (with approximate chemical formula K(Li,AI)3(AI, Si, Rb)40io(F,OH)2) and zinnwaldite (with approximate formula KLiFeAI(AISi3)Oio(OH,F)2), which can also be considered a relative of siderophyllite or polylithionate. Dark mica found in the Extremadura region of Spain is another lithium mica mineral, difficult to chemically identify in comparison to lepidolite and zinnwaldite. Lithium extraction is considered a complex chemical process, perhaps the more so in the case of lithium mica minerals, with the need for multiple unit operations including calcination, leaching, impurity removal and crystallisation, impurity removal typically involving a number of steps to remove a suite of impurities including calcium and other metals, fluorine, boron and sulphate.

[0006] In the lithium field, process economics drives consideration of the following: increasing extraction efficiency, producing value added products in addition to the lithium salt, reducing costs and combinations of these options.

[0007] It is against this background that the process of the present invention has been developed.

SUMMARY OF INVENTION

[0008] In one aspect, the present invention provides a process for producing a lithium salt from a lithium containing material comprising:

(a) leaching the lithium containing material to form a sulphate containing solution;

(b) separating sulphates of elements contained within said lithium containing material by crystallisation from the sulphate containing solution; and

(c) producing a lithium salt.

[0009] The lithium containing material may include, without limitation, any of “run of mine” (ROM) lithium ore, lithium mineral concentrates, lithium containing clays and lithium containing minerals. Without limitation, lithium containing minerals which may be treated according to the process include pegmatite, lepidolite, zinnwaldite, dark mica and other lithium mica minerals which contain - with other elements - potassium, fluorine and rubidium as well as lithium. Treatment of lithium containing minerals such as spodumene is also possible though the process is preferably directed to lithium minerals containing elements such as potassium, rubidium, caesium, rare earth elements and fluorine in substantial quantity, this being more typical of lithium containing micas or lithium containing micaceous materials.

[0010] A plurality of crystallisation steps are preferably included to separate sulphates in step (b). The sulphates to be separated may be determined, dependent on the mineralogy of lithium mineral(s) present within the lithium containing material and in particular dependent on sodium and/or potassium content of the lithium mineral(s) present within the lithium containing material. Preferably, the sulphate compounds are separated utilising the tendency of the alkali- and alkali-earth salts to form complexes with lower solubility than their simple salt components. In preferred embodiments, in particular relating to lithium mica minerals, the exploited group consists of Glauber’s salt (Na2SO4.10H2O), glauberite (Na2Ca(SO4)2) and/or glaserite, a double salt of potassium and sodium sulphate ((K,Na)3Na(SC )2). Separation of glaserite allows separation of a substantial proportion of potassium entering the process, in particular in the form of potassium present within the treated lithium mineral(s) such as lithium micas. The sulphates are preferably recycled to the process, commercialised as an end product or a combination of these options.

[001 1 ] Sulphates are preferably selectively separated in discrete steps, conveniently by selective crystallisation. In one embodiment, Glauber’s salt may be separated in a first crystallisation step and glaserite separated in a further crystallisation step.

[0012] In one embodiment, the sulphate rich liquor following separation of the lithium salt is directed to a Glauber’s salt crystallisation step. Following separation of Glauber’s salt, which removes a substantial portion of sodium, the liquor from Glauber’s salt crystallisation may be directed to a glaserite crystallisation step conducted with selected ratios of Na, K, SO4 and Li to enable precipitation of glaserite. Glaserite may be useful as a fertiliser but its formation also allows removal of a substantial portion of potassium from the process. Glauber’s salt and/or glaserite may also be recycled to form a mixture with lithium containing minerals as described above as, when roasted and solubilised, they assist extraction of lithium in leaching step (a). Glauber’s salt is preferably recycled following heating to remove water of hydration.

[0013] Alternatively, glaserite separation may precede, in a first crystallisation step, Glauber’s salt separation in a further crystallisation step to produce a solution suitable for the direct production of lithium hydroxide by the addition of an alkali, preferably caustic soda.

[0014] The lithium bearing mineral may contain rubidium and/or caesium. Rubidium and potassium deport together and so rubidium may co-crystallise with glaserite in the glaserite crystallisation step. The glaserite crystallisation step may, if preferred, be conducted prior to production of crude lithium carbonate. Alternatively, rubidium may be removed as an alunite by the addition of aluminium sulphate.

[0015] The lithium containing material to be used as a feed to the conversion process desirably comprises a mixture of lithium bearing minerals and a combination of sulphate(s) and further reagents selected from the group consisting of sulphates separated in step (b), sodium sulphate, potassium sulphate and calcium containing salts. The calcium containing salt(s), which are also termed fluxes the addition of which act to prevent sintering during calcination or roasting, may be selected from the group consisting of lime, limestone, glauberite and gypsum, the latter two compounds also being sulphates. The mixture may further include a binder where required for agglomeration, for example by pelletisation, prior to leaching step (a) or calcination.

[0016] Impurities should removed from the pregnant solution, such impurity removal likely requiring a plurality of impurity removal stages selected from the group consisting of neutralisation, calcium precipitation, ion exchange and crystallisation. Cationic impurities, typically multi-valent metal cations, and some anionic impurities, such as phosphate and fluoride, are conveniently removed by a neutralisation step. Calcium may be precipitated preferably as limestone, conveniently after neutralisation. Ion exchange is conducted to remove impurities, such as remnant calcium following calcium precipitation, magnesium, heavy metal ions, boron and fluoride. Ion exchange may comprise a plurality of ion exchange stages to remove the various types of impurity, for example ion exchange stages for 1 ) removal of calcium and heavy metals, 2) removal of boron and 3) removal of fluoride. Ion exchange stage 3) may require prior acidification. As ion exchange stage 3) may elevate calcium levels, pregnant solution from this ion exchange stage is desirably directed to a calcium precipitation stage prior to delivery of pregnant solution to ion exchange stages 1 ) and 2). Each ion exchange stage preferably comprises a plurality of ion exchange columns, for example running in lead, lag and regeneration modes.

[0017] Prior to leaching step (a), the lithium containing material is preferably subjected to calcination - which refers to heat treatment typically of minerals or mineral concentrates to effect structural changes (including, without limitation, phase changes or transformations, decrepitation or solid-state chemical transformations) which facilitate leaching. Calcination may also refer to roasting which conveniently involves the thermal treatment of the lithium containing material in the admixture with one or more reagents which preferably include at least a portion of the separated sulphates from step (b). The terms calcination and roasting are used interchangeably both in this specification and elsewhere.

[0018] Calcination or roasting temperature depends on the phase change to be induced in the metal containing material. Calcination may be conducted in the temperature range 700 to 1300°C, with temperatures between 900 to 1000°C typically applied to lithium containing minerals, such as lithium micas, rather than spodumene where clinker formation above 1100 to 1300°C may be problematic. The calcination residence time is again mineral dependent but would typically be selected in the range of 30 minutes to 90 minutes.

[0019] Desirably, leaching step (a) comprises an aqueous leach, preferably of a calcined mixture of lithium bearing minerals and a combination of sulphate(s) and further reagents as described above to form a pregnant solution comprising lithium sulphate and impurities; and a leach residue. The leaching step (a) is preferably conducted in a plurality of vessels connected in series and operated in a counter-current mode with calcined or roasted mixture being contacted with pregnant solution from an adjacent downstream leach vessel.

[0020] Where lithium concentration in the pregnant solution is less than a threshold, preferably in the range 20-25 g/L, the solution may be concentrated, by evaporation or membrane processing, to increase lithium concentration to enable economic recovery. With low lithium grade minerals, which may include lithium micas, having Li2O content less than perhaps 1 wt%, 0.8% or 0.7 wt%, there is very likely to be a requirement for such concentration to enable lithium recovery.

[0021] The lithium salt produced by the process may be lithium carbonate or lithium hydroxide, the latter being typically in the form of lithium hydroxide monohydrate. Other lithium salts could be produced if required.

[0022] A crude lithium carbonate may be produced by a carbonation process using a carbonate reagent directly, such as sodium carbonate. Alternatively, or additionally, crude lithium carbonate may be produced from the bleed stream, for example as described in International Application No. PCT/AU2023/050560, the contents of which are hereby incorporated herein by reference for all purposes. [0023] Where a crude lithium carbonate is produced, this may be purified by dissolution in aqueous solution and bicarbonation, preferably with pressurised carbon dioxide, pressure preferably being in the range 5 to 15 bar. Carbon dioxide may also be used at ambient pressure for this process step at the expense of slower kinetics.

[0024] The lithium bicarbonate solution from bicarbonation is purified, in particular to remove insoluble impurities following which the solution is decarbonated to produce purified lithium carbonate in a slurry which may be concentrated, if required, prior to purified lithium carbonate separation. Carbon dioxide released by the decarbonation process is preferably recycled to bicarbonation.

[0025] If lithium hydroxide monohydrate is a desired lithium salt, the purified lithium carbonate may be reacted with a hydroxide, conveniently hydrated lime. This reaction forms a filtrate containing lithium hydroxide, and a precipitate of insoluble limestone. Separated filtrate containing cationic impurities may be treated by ion exchange for impurity removal prior to crystallisation of lithium hydroxide monohydrate. Concentration of the lithium hydroxide solution, for example by evaporation or membrane processing, may be required prior to lithium hydroxide monohydrate crystallisation. While lithium hydroxide monohydrate of desired purity may be obtained in a single crystallisation step, a plurality of crystallisation steps may be required.

[0026] Liquors following separation of sulphates, lithium salt (in particular lithium carbonate and/or lithium hydroxide monohydrate) and impurities in upstream process steps are desirably recycled to those upstream process steps as above described. Alternatively, or additionally, because such liquors are likely to contain residual lithium, further processing may be conducted to recover a substantial portion of such residual lithium.

[0027] In one embodiment, such liquors are delithiated to recover residual lithium content, being treated, for example, by a soluble carbonate or carbon dioxide, to precipitate lithium carbonate which may be separated and recovered with the substantial portion of lithium carbonate produced by the process, whether, preferably, as a crude product or a purified product.

[0028] In another embodiment, where liquors contain residual lithium content, even after precipitation of lithium carbonate or lithium hydroxide, these may be further delithiated as described in International Application No. PCT/AU2023/050560, incorporated herein by reference.

[0029] Following delithiation steps, a final brine is desirably directed either to discharge with composition within acceptable discharge limits or, more preferably, directed to a zero liquor discharge unit to produce anhydrous salts for sale or disposal.

[0030] The process as described as advantages in treating low lithium grade materials, in particular lithium mica minerals or micaceous minerals containing lithium to produce a selection of lithium salts. Sulphates may be recovered as marketable commodities and/or recycled as process reagents to the process.

BRIEF DESCRIPTION OF THE DRAWINGS

[0031] Further features 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:

[0032] Figure 1 is a flowsheet for producing lithium carbonate and/or lithium hydroxide according to one embodiment of the present invention.

[0033] Figure 2 is a flowsheet for producing lithium hydroxide according to a further embodiment of the present invention.

[0034] Figure 3 is a schematic flowsheet showing the preferred counter-current leaching scheme for Figures 1 and 2.

DESCRIPTION OF PREFERRED EMBODIMENTS

[0035] Referring to Figure 1 , a lithium mica mineral run of mine material or concentrate 4 - such as lepidolite or zinnwaldite or dark mica (the latter occurring in psammopelitic metasediments as described by Pesquera, A et al., The metasomatic enrichment of Li in psammopelitic units at San Jose-Valdeflorez, Central Iberian Zone, Spain: a new type of lithium deposit, Sci. Rep, (2020), 10, 10828, the contents of which are hereby incorporated herein by reference - is treated in lithium extraction process 1000 for the recovery of lithium hydroxide 190 and/or lithium carbonate 149. As an example, and with reference to description of separation of potassium and sodium sulphate compounds below, lepidolite may contain up to 6.5% potassium and 1 .25% sodium as well as boron and fluorine. Dark mica also contains boron and fluorine and to a lesser extent rubidium and caesium.

Feed Preparation

[0036] A lithium mica containing mixture 5 is formed in feed preparation stage 1 by admixture, with the lithium mica mineral concentrate 4, of further components which may, in summary, be selected from the group consisting of one or more sulphate compounds, one or more fluxes and, where agglomeration is required, a binder.

[0037] Of particular importance is inclusion in mixture 5 of sulphate compounds 4a which desirably include sulphate compounds which are produced within lithium extraction process 1000. Such sulphates (including their hydrates) may be selected from the group consisting of sodium sulphate, potassium sulphate, glauberite, Glauber’s salt, glaserite, gypsum and mixtures of these. In a preferred embodiment, the sulphate compounds include a mixture of sodium sulphate, potassium sulphate, glauberite, Glauber’s salt, glaserite, gypsum, and calcium sulphates generated in the downstream processing units.

[0038] A preferred flux, within mixture 5, is lime or limestone. A further component, acting as a flux, may be a calcium containing residue from downstream calcium precipitation such as solid phases 37 and 46 described below. These fluxes, in dry form, may be applied as a surface coating on the agglomerated calciner feed mixture.

[0039] As agglomeration is to be performed, mixture 5 includes a binder suitable for binding the various components of the mixture 5 together. This may be added in amount effective to achieve agglomeration. In this case, the selected binder is polyvinyl alcohol (PVA) and this may be present in mixture 5 at a content of between 1 to 7 percent by weight. Other binders, as known in the mineral processing art, may also be used in other embodiments.

[0040] The ratio of the above-described components, which may also be described - with the exception of the binder - as reagents, may affect the calcination operation. In the preferred embodiment, 0.4-0.6 weight units of glauberite would be included for every weight unit of lithium mica mineral 4. Additionally, 0.05-0.2 weight units of lime would be included for every weight unit of lithium mica mineral 4. As would be understood by those skilled in the art reading this disclosure, the optimum weight ratios are a function of mineralogy of the lithium mica mineral 4 or, in other embodiments, other minerals including lithium minerals within the lithium containing material.

[0041] Agglomeration of the lithium mica containing mixture 5 may involve pelletisation to provide pellets suitable for calcination with acceptable levels of dust formation. Pelletising may be carried out using process water, process condensate or raw water. In some embodiments, pellets may be provided with a surface coating, such as of fine limestone to optimise pellet integrity.

Calcination or Roasting

[0042] In one embodiment the agglomerated lithium mica containing mixture 5 is then calcined in calcination step 10, employing a natural gas fired calciner of type known in the lithium extraction art, such as a rotary kiln in preferred embodiments, to produce a material more amenable to lithium extraction. In alternative embodiments, calciners that operate with different mechanisms may be used for the heating duty. The calcination step 10 may be conducted at a temperature in the range 700-1300°C dependent on the lithium mineral’s mineralogy. For micaceous material, the preferred calcination temperature range is 850-1000°C.

[0043] The residence time for calcination of the mixture 5 within the rotary kiln 10 is a period of 20 minutes to 4 hours again dependent on lithium mineral’s mineralogy. For mixture 5 of a lithium mica material, the preferred residence time ranges from 30 to 90 minutes.

Leaching

[0044] The calcined material 16 from the rotary kiln is then cooled to less than 100°C to enable the leach 20 to be conducted in water at atmospheric pressure. The calcined material 16 may be discharged into a slurrying vessel to enable expedient transfer of material to the leaching unit operation or leach circuit 20. Calcined material 16 may be slurried with water that may be fresh water, raw water or a combination of process water and recycle streams FW from the downstream process. Process water and recycle streams are preferred sources of water for slurrying. [0045] The solids concentration of the slurry containing calcined material 16 and water FW ranges from 10 to 40 weight% with a preferred solids concentration of at least 25 weight% for the calcined lithium mica material. The leach temperature is determined, in this embodiment by the rotary kiln discharge temperature, typically ranging from 50°C to 90°C.

[0046] In preferred embodiments, a counter-current leach operates as follows to increase the lithium concentration of the final discharge liquor 29. Leach circuit 20 involves one or a plurality of leach vessels 22 operated in series to treat the calcined material 16 with pregnant liquor from the adjacent downstream leach vessel, that is, counter-currently. Preferably, one to five - in this embodiment four - leach vessels 22 are included in leach circuit 20.

[0047] Leach circuit 20 also includes wash units W1 to W3 connected to each leach vessel 22 for washing solids to remove entrained liquor (which may result in lithium and other losses in discharged solids) with fresh water FW. Preferably, one to three - here three wash units W1 to W3 are included in leach circuit 20, as shown in Figure 3. A portion of wash water 26, desirably water from final wash W3, is recycled to vessels 22 of leach circuit 20.

[0048] In embodiments, the pregnant liquor 29 also contains wash water used to displace any entrained liquor in the solids present in the leach slurry. The last leach vessel 22 in the series of leach vessels 21 thus undergoes a final solid liquid separation 28 and washing with water W whereafter filtrate pregnant liquor 29 containing lithium and other value and impurity elements is fed to a downstream primary impurity removal vessel in unit 30 while solid leach residue 27 is discharged from the leach circuit 20. Since lime and limestone is included in the calcine feed mixture the pH of the filtrate pregnant liquor 29 is higher than 7, and likely higher than 8 under standard conditions. Therefore, in the preferred embodiment no additional unit operation is required for the removal of multi valent cations, such as iron, that precipitate at these pH levels.

Primary Impurity Removal

[0049] The pregnant liquor 29 from leach circuit 20 is treated with a reagent in a primary impurity removal stage 30 to increase its pH to higher than 10. The reagents may include any causticisation agent such as lime, hydrated lime, limestone, sodium hydroxide, or potassium hydroxide. Other causticisation agents may be suitable subject to cost and desirability of avoiding addition of impurity elements to the liquor. In this embodiment, hydrated lime 31 from lime slaking unit 32 is used as causticisation agent. The purpose of the primary impurity removal is to remove multivalent cationic impurities as well as some anionic impurities, such as fluoride a typical impurity in lithium mica minerals, by precipitation in a primary impurity removal process.

[0050] The primary impurity removal stage 30, in this embodiment, includes one unit operation, neutralisation, but more may be provided if required. The temperature of the primary impurity removal stage 30 will range from 50°C to 90°C, that is at approximately the leach temperature range though some change in temperature from the leach temperature would typically be expected.

[0051] In some embodiments including the present, where fluoride is present in lithium containing mineral concentrate 4 and thus the pregnant liquor 29, a reagent may be added to the pregnant liquor 29 in primary impurity removal stage 30 in an amount sufficient to precipitate substantially all of the fluoride though some fluorine will remain in the treated liquor 38. Phosphoric acid 33 is a suitable reagent for removal of fluoride in primary impurity removal stage 30.

[0052] The treated slurry is then subjected to a solid-liquid separation 35, conveniently filtration. The solid phase may be washed with wash NW to recover entrained lithium and the separated neutralised liquor 38, or filtrate where filtration is adopted, together with any wash liquor is fed to calcium precipitation unit 40. The solid phase 37, having utility as a flux in view of its substantial calcium content especially in an embodiment where limestone or lime are used for neutralisation in neutralisation stage 30, may be recycled to the feed preparation stage 1 for inclusion in mixture 5 as described above.

Calcium Precipitation

[0053] Since calcium levels in filtrate 38 from the fluoride ion exchange unit 66 of ion exchange stage 60 may typically be elevated interfering with further ion exchange steps, a calcium precipitant - conveniently soda ash which will precipitate insoluble limestone - is added to the filtrate 38 in the calcium precipitation unit 40 enabling precipitation of such calcium in a separate unit operation to neutralisation in primary impurity removal stage 30. The temperature of the calcium precipitation unit 40 may range from 50°C to 95°C depending on the constraint of the calcium specification of the final lithium hydroxide or lithium carbonate.

[0054] The slurry from calcium precipitation unit 40 is then filtered and the solid phase 46 washed to recover entrained lithium. Alternatively, solid phase 46 may be recycled to the feed preparation stage 1 for inclusion in mixture 5 with the same benefit as for solid phase 37 as described above. Filtrate 48 is fed to the following ion exchange stage 60.

Further Impurity Removal

[0055] Ion exchange stage 60 is provided to remove remnant impurities expected to be calcium, magnesium, heavy metal ions, boron and fluorine. Therefore, a series of three independent ion exchange units 62, 64 and 66 - each with duty-specific ion exchange resins in a selected number of ion exchange columns - in this embodiment three columns - are used to remove the impurities and polish the pregnant solution 48 to provide polished pregnant solution 49. Ion exchange units 62, 64 and 66 operate individually in lead, lag and regeneration modes.

[0056] Ion exchange unit 62 removes calcium and heavy metals. A suitable ion exchange resin for this duty is available under the trade name Purolite MTS9500. Flowrate is selected for effective removal of calcium and heavy metals, for example at a flowrate of 8-15 bed volumes per hour.

[0057] Ion exchange unit 64 removes boron. A suitable ion exchange resin for this duty is available under the trade name Amberlite IRA 743. As with ion exchange unit 62, the flowrate is selected for effective removal of boron and may be 8-15 bed volumes per hour.

[0058] Ion exchange unit 66 removes remnant fluoride in the pregnant solution 48 and is conducted upstream of calcium precipitation unit 40 as described above. A suitable ion exchange resin for this duty is available under the trade name Lewatit TP-260. The pregnant solution to this ion exchange unit 66 may require a slight acidic adjustment in pH for optimal operation. The flowrate is selected for effective removal of remnant fluorine. The flowrate in the columns of ion exchange unit 66 is desirably lower than for ion exchange units 62 and 64, for example 5 bed volumes per hour as a limit. The fluoride ion exchange unit 66 is, in this embodiment and desirably, utilised prior to calcium precipitation unit 40.

Evaporation

[0059] Polished pregnant solution 49 is fed to an evaporation stage 70, which in this embodiment includes a single evaporator, for increasing lithium concentration. Desirably, lithium concentration in the evaporated pregnant solution 78 is more than 20 g/L, preferably more than 25 g/L to enable economic lithium recovery. The duty of the evaporation stage 70 will typically range from a volume reduction of 20% to a volume reduction more than 60% depending on the upstream process conditions. The condensate from evaporation stage 70 may be used in feed preparation stage 1 or as a washing liquor, in particular for filtered solids from leach circuit 20.

[0060] For micaceous materials, as lower grade lithium minerals and including the lithium mica material (lepidolite or dark mica) treated in embodiments, evaporation is necessary because the lithium concentration in the pregnant solution 49 should significantly exceed the solubility limit of lithium in an aqueous lithium carbonate environment following evaporation. This is to ensure economically significant precipitation of lithium carbonate in the first lithium carbonate precipitation stage 80. Alternative pregnant lithium solution concentration techniques, such as through use of membrane processing, may be used in other embodiments.

First Lithium Carbonate Precipitation

[0061] The evaporated pregnant solution 78 is fed to a first lithium carbonate precipitation stage 80. The object of precipitation stage 80 is precipitation of a crude lithium carbonate 82.

[0062] In one embodiment, a tank within the lithium carbonate precipitation stage 80 is already charged with a dissolved carbonate, conveniently soda ash at a concentration ranging from 200-320 g/L. Preferably, the soda ash concentration is about 300 g/L. The temperature for the precipitation stage 80 is preferably higher than 90°C and residence time is sufficient, for example 90 minutes, to enable substantially complete precipitation of lithium carbonate as a lithium carbonate slurry 82. [0063] Solid crude lithium carbonate 86 is separated from the slurry, for example by filtration 84. The lithium carbonate filtrate liquor 88 is fed to lithium carbonate decomposition unit 90 while the crude lithium carbonate 86 is washed at the filter(s) to displace entrained impurities. Washing may involve washing with hot water washate 147a from the pure lithium carbonate filtration stage 145. Alternatively, or additionally, heated process water or condensate from evaporation stage 70 may be used for washing. A preferred extent of the wash may vary from 0.5 times to 7 times the weight of the solid crude lithium carbonate 86, depending on the acceptable level of water- soluble impurities.

[0064] In one embodiment, the washate 85 from lithium carbonate filtration 84 is used as a make up liquor to dissolve soda ash 81 for lithium carbonate precipitation 80.

[0065] In another embodiment, the solid lithium carbonate 86 is suitable as battery grade product, in which case it may be dried and packed for shipping.

[0066] In another embodiment, where lithium hydroxide monohydrate is the desired product, the solid lithium carbonate 86 may be fed to the liming unit. However, in another embodiment, where purity of solid lithium carbonate 86 is insufficient, prior bicarbonation is preferred.

Lithium Carbonate Decomposition

[0067] The crude lithium carbonate crystallisation filtrate 88 is treated with sulphuric acid 92 in the lithium carbonate decomposition unit 90 until substantially all lithium carbonate has been decomposed thus producing a rich aqueous sulphate solution 98 suitable for sulphate separation by precipitation in sulphate removal stage 100 which produces sulphates that are usefully exploited in the leach circuit 20.

Sulphate Separation

[0068] The rich aqueous sulphate solution 98 is fed to a Glauber’s salt crystallisation unit (GSU) 105 in sulphate removal stage 100 downstream of lithium carbonate recovery. The GSU 105 may include a flash evaporator to optimise energy balance.

[0069] The GSU receives solution 98 and cools it to close to the freezing point of water, desirably lower than 2°C. In a preferred embodiment, the GSU 105 temperature is in the range -2°C to -3°C. The residence time in the GSU 105 may be in the range 1 hour to 4 hours, with 2 hours being selected in a preferred embodiment. The slurry generated by crystallisation in the GSU 105 is separated, conveniently using a centrifuge 107, to remove Glauber’s Salt from the slurry 106. The process conditions within the GSU result in a remnant solution 108 having no more than 35-40 g/L sulphate ion.

[0070] Separated solid Glauber’s salt 109 may, in embodiments including the present, be recycled to feed preparation stage 1. Such recycle 109 preferably occurs after removal of the water of hydration by heating the solids to 40°C or above.

Glaserite Crystallisation

[0071] Glauber’s salt filtrate 108 is fed to a glaserite precipitator 110 which, for example, operates at a temperature of 20°C to 60°C, preferably 30°C to 40°C. Glaserite precipitator 110 desirably operates under vacuum.

[0072] For effective glaserite precipitation avoiding precipitation of lithium triple salts, glaserite precipitator 110 operates with controlled proportions of sodium, potassium, and lithium sulphates. The proportions of each sulphate are within the range 30-70 wt% Na2SO4, 10-60 wt% IJ2SO4 and 15-50 wt% K2SO4. To achieve such proportions, particularly in continuous mode, it may be necessary to recycle precipitated salts such as Glauber’s salt 109 as described above and/or solutions containing potassium and lithium, such as from the bleed stream 119 within the bleed treatment system (including units 210, 215, 250 in addition to other units as described in International Patent Application No. PCT/AU2023/050560 incorporated herein by reference) to achieve optimum glaserite precipitation behaviour.

[0073] Co-crystallisation of other elements, such as rubidium, may occur in glaserite precipitator 110. Rubidium build up in the circuit is partially controlled in the glaserite precipitator 110 because of the tendency for deportation of rubidium with potassium. Both rubidium and potassium are mainly and efficiently removed by a bleed stream unit 250 described below, and to a lesser extent in the leach residue from unit 28.

[0074] In an alternative embodiment, the glaserite precipitator 110 may be located upstream of first lithium carbonate precipitation stage 80 under conditions, conveniently achieved by introduction to glaserite precipitator 110 of recycle streams as described above for glaserite precipitator 110 above. The objective is to achieve a solution 108 having composition allowing glaserite precipitation.

[0075] The crystallised glaserite is then separated as a wet cake, conveniently by a centrifuge, from the slurry from glaserite precipitator 110. The filtrate 119 contains a significantly reduced amount of potassium together with a reduced amount of rubidium in this embodiment. The glaserite wet cake 118 may be dried and sold as fertiliser or, alternatively, recycled to feed preparation stage 1 for inclusion in the lithium mica containing mixture 5).

[0076] The filtrate 119 from glaserite precipitator 110 is, in embodiments, directed as a bleed to a lithium carbonate precipitation unit 210 for recovery of lithium to minimise lithium losses with further treatment for optimum lithium recovery carried out as described in International Application No. PCT/AU2023/050560, the contents of which are incorporated herein by reference.

[0077] The sulphate removal steps above are necessary for purification of the solution for lithium salt production as described below but also to recover sulphate salts for use in the leach circuit 20 or for export. Such use in the leach circuit 20 reduces requirements for raw sulphates, such as sodium sulphate, for use in the process and enhances process economics. Sale of sulphates may also enhance process economics.

Bicarbonation

[0078] In embodiments including the present, crude lithium carbonate 86, as well as any lithium carbonate solids recovered from the bleed, is suspended in water at a solid content sufficient to produce a lithium concentration of at least 8 g/L once solubilised. The slurry is treated with carbon dioxide in a bicarbonation stage 130 where carbonate ions are converted to bicarbonate ions, further solubilising lithium in a bicarbonated liquor 138. In a preferred such embodiment, the carbon dioxide may be introduced to the bicarbonation stage 130 at a pressure of 5-15 bar to enhance the kinetics of conversion of carbonate ions to bicarbonate ions. In another embodiment, the carbon dioxide may be introduced to the bicarbonation stage 130 at ambient temperature and pressure conditions to achieve the same dissolution effect, typically within 1 -2 hours. [0079] The bicarbonated liquor 138 is then passed through a polishing filter to remove insoluble impurities, likely as fine particles.

Second Lithium Carbonate Crystallisation

[0080] Filtered bicarbonated liquor 138 is then heated in decarbonation stage 140, preferably to a temperature sufficient to cause decarbonation of the lithium bicarbonate to precipitate purified lithium carbonate. The selected temperature for decarbonation is higher than 80°C, preferably higher than 90°C. Carbon dioxide produced by decarbonation can usefully be recycled, for re-use, to the bicarbonation stage 130.

[0081] To obtain a solids density, following decarbonation, suitable for filtration (10 wt% or more), the solution may require concentration. Evaporation may be carried out within the decarbonation stage 140 or a unit operation such as thickening may be employed.

[0082] Once acceptable solids density is obtained, the slurry is filtered 145 with the aqueous phase 146 recycled to the bicarbonation stage 130 while the solids are washed, desirably with deionised water 147 to displace entrained impurities. Alternatively, where thickening is employed, thickener overflow is recycled to the bicarbonation stage 130 and the thickener underflow washed, again with deionised water. The extent of the wash may vary from 0.5 times the weight of the lithium carbonate solids to 7 times the weight of the lithium carbonate solids. The washate 147a is preferably directed to the crude lithium carbonate filtration step 84 described above.

[0083] In one embodiment, a portion of the filtrate or thickener overflow may be diverted, as a bleed 146a, to minimise lithium losses as described in International Patent Application No. PCT/AU2023/050560 incorporated herein by reference. Alternatively, and as shown, bleed 146a may be directed to zero liquor discharge (ZLD) unit 250 which operates as described below.

[0084] In one embodiment, the product lithium carbonate 149 is suitable as a battery grade product in which case the product is dried and packed for shipping. If lithium hydroxide is a required product, the product lithium carbonate 149 and/or the product lithium carbonate 86 is directed to liming stage 150 as described below. Production of Lithium Hydroxide

[0085] Where lithium hydroxide is the desired product lithium salt, lithium carbonate wet cake from decarbonation stage 140 and/or lithium carbonate product 86 is treated in liming stage 150 with hydrated lime 152 from lime slaking unit 32A (which may be the same as lime slaking unit 32) at a temperature higher than 50°C, preferably not exceeding 75°C, to produce limestone as a flux 6 for mixture 5 or a saleable product as well as aqueous lithium hydroxide following separation of the limestone, conveniently by filtration 155. Desirably, the source 151 of hydrated lime is of high purity with low levels of impurities such as silica, sodium, potassium, chloride and so on. The residence time for liming stage 150 is desirably between 30 minutes to 2 hours with a residence time of 1 hour being convenient.

[0086] The filtration 155 of lithium hydroxide is preferably carried out using a plate and frame filter or, alternatively, a combination of a thickener and either a belt vacuum filter or a centrifuge to separate the limestone from the caustic aqueous phase. In one embodiment the limestone is washed with water 156 at a ratio that ranges from 0.5 to 2 times the weight of the limestone in a two stage counter-current decantation thickener unit. Limestone may be calcined at higher than 890°C to generate lime for use in the lime slaking unit to produce hydrated lime for liming stage 150. An advantage of generating lime in this way is that any lithium entrained in the limestone is returned to the process minimising lithium losses.

[0087] Washate 157 may be recycled to leach circuit 20 while the limestone solids are recycled, as a flux 6, to feed preparation stage 1 for admixture with lithium containing material 4.

[0088] The filtrate from liming stage 150 may contain some cationic impurities (mainly calcium) because of reagent contamination and an ion exchange unit 1155 may be included to remove such cationic impurities. As with other ion exchange units in the process, the ion exchange unit 1155 may be operated in lead, lag and regeneration modes using an ion exchange resin, for example that available under the trade name Purolite MTS9500. The ion exchange columns are operated at a flowrate effective to remove cationic impurities, for example 6 to 12 bed volumes per hour to produce a polished aqueous lithium hydroxide stream. [0089] The filtrate 1156, purified by ion exchange, is then subjected to evaporation 160 followed by evaporative crystallisation 165 at temperature ranging from 70°C to 95°C, preferably not exceeding 75°C and under vacuum. The residence time for the evaporative crystallisation may be from 30 minutes to 3 hours, conveniently about 60 minutes.

[0090] Preferably, a single crystalliser may be operated to produce battery grade lithium hydroxide monohydrate (LHM) 190 of desired purity. However, depending on upstream processing efficiency, a plurality of crystallisers - desirably no more than three crystallisers - operating in sequence may be required to achieve the desired LHM purity. LHM is then separated from the liquor, preferably by centrifuge or other filtration step 170. Filtrate 172 is then returned to the process, preferably to lime slaking unit 32, 32A or other upstream process stages.

[0091] Condensate 162 from the evaporator and the crystalliser(s) is desirably recycled to stages such as leach filtration 28, PIR filtration 35, IX column washing, bicarbonation stage 130, and pelletisation. Some of the condensate 162 may also be used to wash crystallised LHM. As to washing of the LHM crystals, with condensate 162 or other suitable washing liquor, this is conducted with a wash ratio preferably ranging from 0.5 to 2 times the weight of the LHM solids. The product LHM 190 is then dried, preferably in a vacuum dryer, to preserve crystal integrity and then packed as a dry material for sale. The atmosphere in all units upstream of and including the liming reactors is in the preferred embodiment composed of CO2 free air or other inert gases such as nitrogen, to prevent the formation of lithium carbonate.

Lithium Recovery in Bleed

[0092] It is desirable to minimise lithium losses in aqueous streams within the process. To this end, in one embodiment, filtrate 119 from the glaserite precipitator 110 is fed to a lithium carbonate bleed crystallisation unit 210 to reduce lithium concentration in the bleed stream. The flow rate is selected to enable lithium carbonate crystallisation and, to this end, may be relatively slow. Alternatively, the unit process is conducted in batch processing mode. Conveniently, the lithium carbonate crystallisation unit 210 may comprise tank(s) containing a charge of dissolved soda ash 212 at a concentration ranging from 200 to 320 g/L, conveniently 300 g/L, as described above for the first lithium carbonate crystallisation stage 80. The crystallisation temperature is preferably higher than 90°C and the residence time may, for example, be 90 minutes.

[0093] The obtained lithium carbonate slurry is then filtered 215 using a centrifuge, plate and frame pressure filters or belt filters, to obtain a lithium carbonate wet cake 219 and a lithium depleted liquor 218. The obtained lithium carbonate wet cake 219 is conveniently - and as in this embodiment - directed to bicarbonation stage 130.

Bleed Treatment Unit

[0094] In one embodiment, lithium depleted liquor 218 from filter 215 is treated, together with bleed 146a, in a bleed treatment unit to concentrate the brine to within acceptable brine discharge limits. A zero liquor discharge (ZLD) unit 250 may, as known in the art, be utilised to produce anhydrous salts 256 for sale or disposal. Condensate 258 from the ZLD unit 250 may be recycled to the upstream process. For example, in one embodiment, the condensate 258 from unit 250 may be recycled to leach circuit 20 for washing residue solids with wash 26 following leaching of the lithium containing mixture 5. In an alternative embodiment, as described above, lithium depleted liquor 218 may be processed to recover lithium in several units as described in Australian Provisional Application No. 2022901813 as incorporated herein by reference.

Direct Production of Lithium Hydroxide

[0095] As described above with reference to Figures 1 and 2, lithium hydroxide monohydrate 190 was indirectly produced from lithium hydroxide via lithium carbonate. Alternatively, referring to Figure 2, lithium hydroxide 390 may be obtained from evaporated pregnant solution 78 from evaporation stage 70 in process 1100 as follows.

[0096] Pregnant solution 78 is fed to glaserite precipitator 310 which operates at 20°C to 60°C, preferably 30°C to 40°C. Preferably, glaserite precipitator 310 operates under vacuum. For effective glaserite precipitation avoiding precipitation of lithium triple salts, glaserite precipitator 310 operates with controlled proportions of sodium, potassium, and lithium sulphates. The proportions of each sulphate are within the range 30-70 wt% Na2SO4, 10-60 wt% U2SO4 and 15-50 wt% K2SO4. To achieve such proportions, particularly in continuous mode, it may be necessary - as shown in Figure 3 - to recycle salts precipitated such as Glauber’s salt as described above and/or solutions containing potassium and lithium, such as from the bleed stream 119 within the bleed treatment system (including units 210, 215, 250 in addition to the units described in International Patent Application No. PCT/AU2023/050560 incorporated herein by reference) to achieve optimum glaserite precipitation behaviour.

[0097] Other impurities, such as rubidium, are likely to co-crystallise in the glaserite precipitator 310. Rubidium build-up in the steady state circuit is desirably and conveniently controlled in the glaserite precipitator 310 because of the deportation of rubidium with potassium. Both of these elements may be efficiently removed by the bleed stream unit 250, for example a ZLD unit 250 as described above. Alternatively, an alunite precipitation unit may be used to remove rubidium and potassium.

[0098] Glaserite wet cake and a potassium depleted filtrate 316 is separated from the slurry generated in glaserite precipitator 310, preferably by a centrifuge 315. The glaserite wet cake 318 may then be dried and sold as fertiliser. Alternatively, glaserite wet cake 318 may be recycled to feed preparation stage 1 for inclusion in mixture 5 for roasting. A portion of glaserite wet cake 318 may be recycled to the glaserite precipitator 310 for controlling the potassium tenor for glaserite crystallisation.

[0099] Potassium depleted filtrate 316 is treated with sodium hydroxide in causticisation stage 320 at a stoichiometric excess, for example 2.5% to 5% stoichiometric excess, to the lithium content in the concentrated pregnant solution 78. Residence time may be no more than 30 minutes. The sodium sulphate rich solution 319 is then fed to Glauber’s salt crystalliser 330, which - in this embodiment - follows glaserite separation by filtration 315.

[00100] The Glauber’s salt crystalliser 330, which may include a flash evaporator to optimise the circuit’s energy balance, receives pregnant liquor solution 319 and crystallises Glauber’s salt by cooling, desirably at a temperature less than 2°C. In a preferred embodiment, the crystallisation temperature in Glauber’s salt crystalliser 330 is -2°C to -3°C. residence time in Glauber’s salt crystalliser 330 may be in the range 1 to 4 hours, for example 2 hours. Glauber’s salt 337 is separated from the product slurry 332, preferably by centrifuge 335. The separated liquor stream 338 has no more than 35-40 g/L sulphate ions.

[00101] Glauber’s salt 337 is recycled to feed preparation stage 1 for inclusion in mixture 5 for roasting. Preferably, such recycle 337 occurs after heating of the Glauber’s salt to a temperature of 40°C or greater to remove the water of hydration. A portion of the product slurry 326 may be returned to the glaserite precipitator 310 to achieve the required solution composition for glaserite crystallisation.

[00102] Separated liquor stream 338 is then subjected to evaporation 340 and then evaporative crystallisation 350 at temperature in the range 70°C to 95°C, in preferred embodiments at 75°C under vacuum. Evaporation stage 340 may be omitted if lithium concentration in separated liquor stream 338 is greater than about 20 g/L. A bleed 342 may be required from the evaporator 340 if impurity levels - such as of sodium and potassium - are unacceptably high in the discharge. Evaporative crystallisation 350 residence time may be selected in the range 30 minutes to 3 hours, preferably 60 minutes.

[00103] Preferably, a single crystalliser may be operated to produce battery grade lithium hydroxide monohydrate (LHM) 390 of desired purity. However, depending on upstream processing efficiency, a plurality of crystallisers - desirably no more than three crystallisers - operating in sequence may be required to achieve the desired LHM purity. LHM 390 is then separated from the liquor 358, preferably by centrifuge or other filtration step 360. Filtrate 362 is then returned to the process, preferably to causticisation stage 320 or other upstream process stages.

[00104] As to washing of the LHM crystals, with condensate or other suitable washing liquor, this is conducted with a wash ratio preferably ranging from 0.5 to 2 times the weight of the LHM solids. The product LHM 390 is then dried, preferably in a vacuum dryer, to preserve crystal integrity and then packed as a dry material for sale.

[00105] It is desirable to minimise lithium losses in aqueous streams within the process. To this end, in one embodiment, such streams, for example a bleed 342 from the evaporation and evaporative crystallisation stages 340 and 350 may be fed to a lithium carbonate bleed crystallisation unit 210 to reduce lithium concentration in the bleed stream. In this embodiment, lithium carbonate is crystallised in a slurry 212 by sparging of liquor 342 with carbon dioxide 212A in a carbonation tank. The crystallisation temperature is higher than 20°C and preferably more than 80°C to prevent lithium bicarbonate formation. [00106] Lithium carbonate 219A is then separated, by filtration or centrifugation 215, from obtained lithium carbonate slurry 212 after which the lithium depleted liquor 218 may, as above described, be directed to zero liquid discharge (ZLD) unit 250 or may be treated as described in Australian Provisional Application No. 2022901813 incorporated herein by reference. The obtained lithium carbonate wet cake 219A is, in this embodiment, directed to primary impurity removal stage 30 or, alternatively, to the lime slaking unit 32.

[00107] The zero liquor discharge (ZLD) unit 250 may, as known in the art, be utilised to produce anhydrous salts 256 for sale or disposal. Condensate from the ZLD unit 250 may be recycled to the upstream process. For example, in one embodiment, the condensate 258 may be recycled to leach circuit 20 for washing residue solids following leaching of the lithium containing mixture 5.

[00108] The embodiments of the process described above is expected to achieve at least the following advantages:

1 ) Sulphate roast reagents are recycled within the process.

2) Requirement for sulphuric acid transport to the processing facility is avoided.

3) Ability to pelletise kiln feed provides a mechanism for dust control of fine material within the kiln.

[00109] Those skilled in the art will appreciate that the process 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, features, formulations and compounds 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.

[00110] 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.

[00111] Each document, reference, patent application or patent cited in this text is expressly incorporated herein in their entirety by reference, which means that it should be read and considered by the reader as part of this text. That the document, reference, patent application or patent cited in this text is not repeated in this text is merely for reasons of conciseness.

[00112] The invention described herein may include one or more range of values (eg. size, displacement and field strength 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.