A process for producing lithium salts

Abstract

A process (1000) for producing a lithium salt (190) by treating a particulate lithium containing material containing lithium bearing minerals comprising pressure leaching (20) the lithium containing material with concentrated sulphuric acid to form a pregnant solution (22) containing lithium sulphate as a source of lithium for a selected lithium salt for production (190) and impurities; removing the impurities in a series of steps (30, 40, 50, 60, 70) including removal (70) of at least one sulphate compound contained in the pregnant solution, said at least one sulphate compound containing at least one of potassium and sodium; and producing the selected lithium salt (190) following impurity removal (30, 40, 50, 60, 70).

Description

A Process for Producing Lithium SaltsTECHNICAL FIELD

[0001] The present invention relates to a process for producing a lithium salt such as lithium carbonate or 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, lithium sulphate 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 or lithium metal. More modem 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)s(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. Lithium extraction is considered a complex chemical process, perhaps the more so for lithium mica and mica type minerals, with the need for multiple unit operations including calcination, leaching, impurity removal, electrolysis forlithium metal and crystallisation for lithium salts, typically involving a number of crystallisation steps.

[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. Where lithium prices are comparatively low, such considerations become more acute.

[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 by treating a particulate lithium containing material containing lithium bearing minerals comprising: pressure leaching the lithium containing material with concentrated sulphuric acid to form a pregnant solution containing lithium sulphate as a source of lithium for a selected lithium salt for production and impurities; removing the impurities in a series of steps including removal of at least one sulphate compound contained in the pregnant solution, said at least one sulphate compound containing at least one of potassium and sodium; and producing the selected lithium salt following impurity removal.

[0009] The pressure leaching step (a) may be conducted in a plurality of pressure vessels or autoclaves, preferably operated in parallel, with the particulate lithium bearing material being preferably contacted with pregnant solution but in some cases may require additional aqueous streams such as condensate or process liquors from downstream processing vessels. The lithium containing material may be presented as a slurry to the autoclave(s), preferably following pre-heating. The slurry comprises the lithium containing material and concentrated sulphuric acid. The slurry may also comprise an additional aqueous stream, such as condensate or process water, directed from at least one downstream processing vessel.

[0010] Pressure leaching step (a) is preferably conducted at temperature above 150°C, more preferably 200°C, preferably below 300°C and most preferably at about 250°C.

[0011] Pressure leaching step (a) is desirably carried out with a molar excess of sulphuric acid relative to acid extractable components including multi-valent metal ions, and mineral acid consumers. The excess will vary depending on the lithium containing material composition and, in particular, its mineralogy as reflected by a chemical formula, for example as exemplified below. In one embodiment for dark mica, at least 100 kg sulphuric acid per tonne of feed dark mica ore and the empirically determined optimum acid requirement is 400 kg sulphuric acid per tonne of feed dark mica ore. Sulphuric acid is desirably dissolved in process water or a source of water available within the process to reduce requirements for fresh water.

[0012] A discharge slurry from the autoclave(s), where used as described above, is typically cooled prior to further processing. Flash cooling is convenient and preferred with recovered heat available for preheating of the slurry of lithium containing material presented to the autoclave(s).

[0013] Conveniently, a substantial proportion of the at least one sulphate compound containing sodium and / or potassium is separated in step (b) by crystallisation and precipitation. The sulphate(s) to be separated - whether by crystallisation or otherwise - may be selected, 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 at least one sulphate compound is 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, the at least one sulphate compound is selected from the group consisting of Glauber’s salt (Na2SO4.10H2O), glauberite (Na2Ca(SO4)2) and / or glaserite, a double salt of potassium and sodium sulphate ((K,Na)3Na(SO4)2). Where, the pregnant solution contains a plurality of sulphate compounds containing sodium and potassium, for example Glauber’s salt and glaserite, the sulphate compounds may be precipitated separately by selective crystallisation. Separation of the at least one sulphate compound follows a primary impurity removal step comprising neutralisation of the pregnant solution.

[0014] In one embodiment, the sulphate rich liquor obtained after a neutralisation involving causticisation, which is the addition of caustic soda (sodium hydroxide) in excess of lithium stoichiometry to the pregnant solution, comprises Glauber’s salt. In this case, the sulphate rich liquor containing Glauber’s salt is directed to a Glauber’s salt crystallisation step for removal of the Glauber’s salt. Crystallisation of Glauber’s salt desirably includes chilling of the sulphate rich liquor in a series of steps to temperatures from less than 10°C and higher than -15°C. In the preferred embodiment, two crystallisation stages are used wherein Glauber’s salt is initially removed after crystallisation at 0°C, by filtration, followed by a second crystallisation and filtration below 0°C, for example at -5°C. In another example, the second crystallisation is conducted at -10°C, followed by filtration. As will be understood by practitioners in the field a wide selection of conditions may be used for Glauber’s salt removal. Sulphate may be removed in other forms in other embodiments.

[0015] Impurities other than the at least one sulphate compound containing sodium and / or potassium, as described above, may be removed from the pregnant solution in a sequence or series of steps comprising a plurality of impurity removal stages. Conveniently, the plurality of impurity removal stages is selected from the group consisting of neutralisation, calcium and magnesium 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, for example using lime and / or limestone, to neutralise excess sulphuric acid. Above a threshold concentration, fluoride may be removed by reaction of the pregnant solution with phosphoric acid and lime. The impurity removal steps, other than separation of the at least one sulphate compound, are preferably conducted prior to the sulphate separation step.

[0016] Calcium may be precipitated preferably as limestone, conveniently after prior neutralisation, and preferably after the addition of caustic soda (sodium hydroxide) and soda ash (sodium carbonate).

[0017] Ion exchange is preferably conducted to decrease the concentration of residual impurities, such as remnant calcium following calcium precipitation, magnesium, heavy metal ions, boron and fluoride. An ion exchange step may comprise a plurality of ion exchange stages. 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 ofcalcium 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 or removal stage prior to delivery of pregnant solution to ion exchange stages 1 ) and 2).

[0018] Further, it may be desirable to conduct evaporation of the pregnant solution or slurry following leaching step (a). This both concentrates lithium sulphate and sulphuric acid which may assist in conserving sulphuric acid and reducing the volume of liquor to be neutralised in a following neutralisation step for removal of impurities. In one embodiment, this would reduce consumption of lime or limestone conveniently used for neutralisation. A portion of the evaporated pregnant solution is desirably recycled to leaching step (a).

[0019] Sulphuric acid production, for example by sulphur burning, is preferably integrated with the process, in particular leaching step (a), with a view to energy efficiency in the process and consequential reduction of carbon dioxide emissions.

[0020] Desirably, the lithium containing material is not calcined or otherwise heat treated prior to pressure leaching. This reduces energy costs and potential carbon costs associated with energy production.

[0021] The particulate 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 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, rubidium, caesium and rare earth elements as well as lithium. Treatment of lithium minerals such as spodumene is also possible though the process is advantageously directed to lithium minerals containing elements such as potassium, rubidium, caesium and fluorine in substantial quantity, this being more typical of lithium containing micas or lithium containing micaceous materials. Rubidium and / or caesium may be recovered from the sulphate rich liquor where economical to do so. The process is particularly advantageous for producing a lithium salt from dark mica.

[0022] The selected lithium salt may be any lithium salt of commercial interest, preferably lithium hydroxide monohydrate (LHM) or lithium carbonate. The lithium salt is preferably produced at battery grade.

[0023] Where lithium concentration in pregnant solution is less than a threshold, for example in the range 1-10 g / L, the solution may be concentrated, by evaporation or membrane processing, to increase lithium concentration in one or more concentration steps with the object of promoting crystallisation. A primary concentration step is desirably conducted prior to neutralisation and impurity removal and a secondary pregnant liquor concentration step is desirably conducted downstream of the primary concentration step prior to removing sulphate salts, for example after ion exchange as described above. In preferred embodiments, a third concentration step is required after the removal of sulphate and before the lithium salt is produced by crystallisation in a crude form, that is below battery or required grade, with further crystallisation being conducted to deliver the required battery grade product, as described below.

[0024] If lithium hydroxide monohydrate is a desired lithium salt, the purified lithium sulphate may be reacted with a hydroxide, conveniently sodium hydroxide. This reaction forms a filtrate containing aqueous lithium hydroxide and aqueous sodium sulphate. 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 where the first lithium hydroxide monohydrate product crystallised is in a crude form below battery or required grade. The same applies mutatis mutandis to other selected lithium salt products, for example lithium carbonate.

[0025] Liquors following separation of sulphates and lithium salt(s), for example a barren liquor from crystallisation, are desirably recycled to 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.

[0026] The process desirably includes at least one magnetic impurity removal step. A magnetic impurity removal step may be conducted, for example, on all or selectedaqueous streams in the process. Alternatively, or additionally, magnetic impurity removal may be conducted on slurry streams or dry product streams in the process.

[0027] Where liquors contain residual lithium content, even after crystallisation of the preferred lithium salt, preferably lithium hydroxide monohydrate or lithium carbonate, such liquors may be further delithiated as described in International Patent Publication No. W02024000013, the contents of which are hereby incorporated herein by reference for all purposes.

[0028] 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 or dry salts for sale or disposal.

[0029] The above process enables production of a lithium salt from minerals, in particular mica minerals, having complex mineralogy. This may be done consistently with circular economy principles in terms of recycling of process streams, high lithium extraction and high energy efficiency reducing carbon footprint of the process.BRIEF DESCRIPTION OF THE DRAWINGS

[0030] Further features of the process for producing 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:

[0031] Figure 1 is a flowsheet for producing battery grade lithium hydroxide according to one embodiment of the present invention.DESCRIPTION OF PREFERRED EMBODIMENTSFeed Preparation

[0032] Referring to Figure 1 , lithium containing aluminosilicate mineral(s) in the form of run of mine material is beneficiated by techniques such as crushing, grinding, flotation, heavy media separation and magnetic impurity removal in some embodiments. Whole of ore leaching may be conducted in other embodiments and this may only requirecrushing and grinding to produce a particulate feedstock. In either of these embodiments, the resulting lithium containing mineral feedstock 4 is treated in lithium extraction process 1000 for the production of lithium hydroxide 190. It will be understood that process 1000 is not limited to production of lithium hydroxide, lithium carbonate may also be produced using the process with differences in the final production steps of neutralisation and crystallisation. Production of other lithium salts is also possible using process 1000 with final production steps following purification being varied accordingly.

[0033] In this preferred embodiment, the lithium aluminosilicate mineral includes a phyllosilicate in the form of fine grained lithium mica mineral - not being classified as lepidolite or zinnwaldite and known as a ‘dark mica’ as described, for example, in 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, Sc / . Rep., (2020), 10, 10828, the contents of which are hereby incorporated herein by reference. A deposit of such material is located near Caceres, Spain. As an example, and with reference to description of separation of potassium and sodium sulphate compounds below, the dark mica may contain about 0.6-1.0 wt% Li2O, 6-10 wt% K2O, CS2O up to 3 wt%, Rb2O up to 0.5 wt% and F up to 8 wt%. The process is not restricted to dark mica and the process may be applied to lithium mica minerals generally including lepidolite, and zinnwaldite.

[0034] Notably, before leaching some mica minerals may require pre-processing such as a thermal treatment or calcination typical of treatment schemes for many lithium minerals which depend on a phase transformation to make the material tractable or leachable for extraction of lithium. However, other mica minerals such as dark mica, the processing of which is described here, do not require pre-treatment by high temperature calcination which is advantageous in terms of avoidance of energy costs associated with heat treatment or calcination. It will be appreciated that the mineralogy of lithium micas is complex and the process described herein has been developed to address such complexities. However, in principle, the process may be applied to other lithium aluminosilicate minerals in other embodiments subject to the mineral tractability to leaching by sulphuric acid without prior calcination. For example, difficulties would likely be encountered with application to a-spodumene leaching in the absence of heat treatment to convert it to [3-spodumene.Leaching

[0035] Leaching involves leaching of the lithium containing mineral feedstock 4 in pressure vessel(s) or autoclave(s) comprised within leach circuit 20. The autoclave(s) may be arranged in series or parallel.

[0036] The lithium containing mineral feedstock 4 is slurried in agitated slurry preparation tank(s) to form a lithium mica containing slurry having a solids density in a wide pumpable range preferably spanning 5 to 60%. Selected solids density may, as appreciated by those skilled in lithium mica hydrometallurgy, be dependent on the pump selection. Slurrying water may be selected from any plant available process water source such as municipal water, condensate, recirculating process liquors, demineralised (or purified) water or hydroxide circuit stream bleed. The slurrying water is preferably selected to reduce the amount of fresh water required as a reagent to a hydroxide circuit 1100 as described further below. In the embodiment shown, the slurrying water 124 is a recycle condensate stream from evaporation stage 120.

[0037] The lithium mica containing slurry is conveniently collected in agitated storage tank(s) that act as buffer storage. From these tanks, slurry is withdrawn at a nominal rate to surge tanks in preparation for pre-heating via heat exchangers (not shown). Slurry water 124 is from a hot source (evaporation stage 120) and available at a temperature >70°C to minimise energy loss in the hydroxide circuit 1100. The preheaters increase the temperature of the slurry, preferably to higher than 150°C, using energy from various streams out of downstream equipment, such as steam from flash vessels that reduce the pressure of the discharged autoclave slurry stream.

[0038] The hot slurry is then fed to one or more pressure vessel(s) or autoclave(s) that operates, in continuous mode, at a temperature preferably higher than 150°C, dependent on the lithium containing mineral feedstock 4. The Applicant has found that, for dark mica as described above, a temperature of 250°C is required for acceptable kinetics. In preferred embodiments, concentrated sulphuric acid is fed into the autoclave at a rate suitable to maintain a selected sulphuric acid to dark mica feed ratio, preferably in excess of 100 kg acid per tonne of ore, more preferably 200 kg acid per tonne of ore, most preferably about 400 kg acid per tonne of ore, the latter being theempirically determined optimum. Depending on the nature of the lithium mineral containing feedstock 4, the residence time of the slurry in the autoclave may range from 30 to 480 minutes. For dark mica, the Applicant has found 90 minutes to be optimum but the process can be conducted in any efficient manner from both temperature and residence time perspectives.

[0039] It will be appreciated that this embodiment for dark mica does not require a heat treatment or calcination of the lithium mineral containing feedstock 4. This allows a saving in costs and yet the Applicant has found that economic extractions of lithium and other elements may be obtained without such heat treatment.

[0040] In the present embodiment, sulphuric acid 18 is generated on-site in a sulphur burner 15 using sulphur 15a as feed reagent. In this way, sulphuric acid production is integrated with lithium salt production and, in particular, leach circuit 20. The highly exothermic nature of sulphuric acid production from sulphur, combined with the quantity of sulphuric acid required for process 1000, provides a means by which most or all processing plant steam is produced in unit 15 and is generally beneficial for the energy efficiency of process 1000 thereby reducing carbon dioxide emissions. Additionally, for the current embodiment for dark mica a significant excess of steam is produced providing an opportunity to generate additional electric power for the process through co-generation as understood in the hydrometallurgy art. Therefore, the embodiment shown in Figure 1 depicts a lithium extraction process that has a significantly lower greenhouse gas emission or carbon footprint compared to current large scale lithium extraction and refining facilities. Alternatively, the sulphuric acid 18 can be purchased and imported to site.

[0041] Lithium sulphate containing slurry 22 is continuously discharged from the autoclave(s) into flash vessels, the number of which depends on the required energy recovery. In preferred embodiments, three flash vessels are used covering high pressure flashing, medium pressure flashing and low pressure flashing. Steam from the flash vessels may then ultimately be used to pre-heat the slurry being fed to the autoclave(s) or for other heating duties in the process.

[0042] The discharged lithium sulphate containing slurry or pregnant liquor or solution 22 is then collected in a tank in the leach area before being filtered and washed in a filter comprised within filtration stage 25. Conveniently, the filter is preferably a plateand frame pressure filter, preferably with a core-blow function. Different filtration equipment such as a belt filter may be used in alternative embodiments. The leach residue 26 is filtered, preferably to a moisture level less than the transportable moisture limit of the filter cake while the acidic pregnant liquor 29 is collected in a filtrate tank.

[0043] The pregnant liquor 22 is, in the illustrated embodiment, fed to an evaporation stage 25 which may include one or more leach evaporator(s) to increase the lithium concentration of the lithium sulphate containing liquor to a level suitable for further downstream processing. In alternative embodiments, it may be possible to use other concentration unit operations, for example through membrane processing. As will be appreciated from the above description of the composition of dark mica, the lithium content of pregnant liquor 22, without the indicated recycle of stream 124, would be relatively low typically making such lithium concentration necessary. Desirably, the increase in lithium concentration should be to a value of at least 3 g / L lithium, preferably more than 6 g / L lithium.

[0044] Evaporation stage 25 also results in concentration of sulphuric acid which assists in conserving sulphuric acid and reducing the volume of liquor to be neutralised in neutralisation stage 30 for primary impurity removal of impurities. This would reduce consumption of neutralisation agent as described further below.

[0045] In some cases, a return stream 124 of the evaporator discharge may be fed back to the slurry preparation tank(s) of leach circuit 20, thus increasing the lithium concentration of the feed slurry to the leach circuit 20 and therefore the lithium concentration in the discharge from the leach circuit 20. In embodiments, the return stream 124 may comprise up to 70 wt% of the discharge from evaporation stage 120. For dark mica, the return stream 124 could be in this range too but is preferably in the range 40 to 60% of the discharge from evaporation stage 120, more preferably about 40% of the discharge from evaporation stage 120.Primary Impurity Removal

[0046] The pregnant liquor 29A from leach circuit 20 is treated with a reagent or reagents in a primary impurity removal or neutralisation stage 30 to increase its pH to higher than 6. The reagents may include any combination of causticisation agent such as lime, hydrated lime, limestone, sodium hydroxide, or potassium hydroxide. Othercausticisation agents may be suitable subject to cost and desirability of avoiding addition of impurity elements to the liquor. In this embodiment, limestone is added as a 30 wt% slurry to a target pH of about 5-6 after which hydrated lime 31 from a lime slaker in unit 32 is used for neutralisation to a pH higher than 6. The purpose of the primary impurity removal or neutralisation unit is to remove multivalent cationic impurities as well as some anionic impurities, such as phosphate and fluoride, if required, by precipitation in a primary impurity removal or neutralisation process.

[0047] The primary impurity removal stage 30, in this embodiment, includes one unit operation but more may be provided if required. The temperature of the primary impurity removal stage 30 will typically range from 40°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.

[0048] In some embodiments, including the present, where fluoride is present at elevated levels in lithium mineral containing feedstock 4 and thus the pregnant liquor 29A, a reagent may be added to the pregnant liquor 29A in primary impurity removal stage 30 in an amount sufficient to precipitate substantially all of the fluoride as apatite, fluorite or a hydroxyapatite variant though some fluorine will remain in the treated liquor. Phosphoric acid in combination with hydrated lime is a suitable combination of reagents for removal of fluoride in primary impurity removal stage 30.

[0049] The treated slurry 34 is then subjected to a solid-liquid separation 35, conveniently filtration in a suitable filter, conveniently a plate and frame press filter, preferably with a core-blow function. Different filtration equipment such as a belt filter may be used in alternative embodiments. The solid phase is preferably washed to recover entrained lithium and the separated neutralised liquor 38, or filtrate where filtration is adopted, is fed to calcium precipitation unit 40. Wash liquor from the filter in unit 35 in some embodiments may be directed to unit 40 or alternatively in other embodiments be directed to unit 32 for use as slurry water. The solid gyplime phase 37, may be recycled in part to lime slaking unit 32. Alternatively, the gyplime phase 37 may in the present embodiment have utility as a building material, a component of fertiliser, or as flux in view of its substantial calcium content.

[0050] In some cases, where elevated levels of fluoride are present in the treated pregnant liquor 38, a fluoride ion exchange unit may be included to remove remnantfluoride. Ion exchange columns are included - as known in the art of ion exchange in lithium processing plants - to operate in lead, lag and regeneration modes. These ion exchange columns contain a fluoride selective cation exchange resin, such as a that available from Lenntech under the trade name Lewatit TP-260, to remove remnant fluoride. This resin is a weakly acidic, macroporous cation exchange resin with chelating amino methyl phosphonic acid groups to capture remnant fluoride. The treated pregnant liquor 38 may require a slight acidic adjustment for optimal operation at pH below 6. The flowrate in these columns desirably does not exceed 5 bed volumes per hour though a flowrate effective for fluoride removal may be set as required. Preferably, the Lewatit TP-260 ion exchange resin is conditioned to target fluoride removal by a dilute solution of aluminium sulphate. Regeneration is carried out using a strong acid such as dilute hydrochloric acid, or alternatively, dilute sulphuric acid. As will be understood, this fluoride ion exchange step may not be necessary where fluoride levels in neutralised liquor 38 are low.Calcium and Magnesium Precipitation

[0051] Since calcium and magnesium levels in neutralised liquor 38 either from the primary impurity removal stage 30 or fluoride ion exchange stage (if used) may typically be elevated interfering with further purification steps, a calcium and magnesium precipitant - conveniently caustic soda 132b and soda ash 41 which will precipitate insoluble limestone and insoluble brucite - is added to the neutralised liquor 38 in precipitation unit 40. Soda ash 41 is obtained from neutralisation reagent storage unit 42 and caustic soda 132b is obtained from sodium hydroxide stock 130.

[0052] The temperature of the calcium precipitation unit 40 may range from 50°C to 95°C depending on the required calcium specification of the final lithium hydroxide or lithium carbonate product. Typically, to achieve a calcium concentration of less than 20 mg / L in stream 48, a temperature exceeding 90°C is required.

[0053] The discharge slurry from calcium precipitation unit 40 is then filtered and the solid phase 43 may be washed to recover entrained lithium.Further Impurity Removal

[0054] Ion exchange stage 50 is provided to remove remnant impurities expected to be calcium, magnesium, heavy metal ions, boron and fluorine unless the fluorine ionexchange step described above is included. Preferably, a series of two independent ion exchange units (not shown) - each with duty-specific ion exchange resins in a selected number of ion exchange columns - are used to remove the impurities and polish the pregnant solution 48 to provide polished pregnant solution 52. The ion exchange units operate individually in lead, lag and regeneration modes.

[0055] In a preferred embodiment, the first ion exchange unit removes calcium and heavy metals in a first set of ion exchange columns. A suitable ion exchange resin for this duty is available under the trade name Puromet MTS9500 from Purolite. The Puromet MTS9500 resin is a macroporous aminophosphonic chelating resin.

[0056] Flowrate is selected for effective removal of calcium and heavy metals, for example at a flowrate of 8-15 bed volumes per hour. In a preferred embodiment, the Puromet 9500 resin is used without conditioning with protons being exchanged. In alternative embodiments, monovalent ions may be used for conditioning. For example, a lithium or sodium containing liquor may be used to condition the ion exchange column(s).

[0057] A second ion exchange unit removes boron, if required, in a second set of ion exchange columns. A suitable ion exchange resin for this duty is available from Sigma Aldrich under the trade name Amberlite IRA 743, a borate specific chelating resin for removal of boron species from aqueous solutions. As with ion exchange unit 62, the flowrate is selected for effective removal of boron and may be 8-15 bed volumes per hour. Amberlite IRA 743 ion exchange resin may be conditioned with dilute sodium hydroxide while regeneration may be achieved using dilute hydrochloric acid in a preferred embodiment or sulphuric acid in an alternative embodiment.Evaporation

[0058] Polished pregnant solution 52 is fed to an evaporation stage 55, which in this embodiment includes a single evaporator, for increasing lithium concentration. As noted previously, dark mica has a low lithium concentration and this is also true of the pregnant liquor 29A and the following lithium ‘rich’ streams. Desirably, lithium concentration in the evaporated pregnant solution 57 is more than 10 g / L, preferably more than 17 g / L. The duty of the evaporation stage 55 will typically range from a volume reduction of 20% to a volume reduction more than 80% depending on theupstream process conditions. In the preferred embodiment, the evaporator duty ranges between 50% to no more than 70% of the feed volume operating at a temperature of higher than 40°C under vacuum, preferably more than 60°C under vacuum, more preferably more than 80°C under vacuum.

[0059] The condensate from evaporation stage 55 is desirably used elsewhere in process 1000, for example in feed preparation stage 1 or as a washing liquor, in particular for filtered solids from leach circuit 20.Causticisation

[0060] The discharged evaporated pregnant solution 57 is fed to causticisation stage 60 where it is treated with sodium hydroxide solution 132a from sodium hydroxide stock 130. Sodium hydroxide solution 132a is conveniently a 50 wt% sodium hydroxide solution, in an agitated mixing tank. The object of causticisation stage 60 is to form a sulphate rich aqueous lithium hydroxide containing stream 66 comprising, in summary, aqueous lithium hydroxide and aqueous sodium sulphate amongst other sulphates. The operating temperature of the causticisation stage 60 is determined, in this embodiment, by the heat of mixing caustic soda as well as the temperature of the discharged evaporated pregnant solution 57 in turn determined by the operating temperature of the evaporator of evaporation stage 55.

[0061] The aqueous lithium hydroxide stream 62 may contain fines and these may be removed by a fines or polishing filter 65. The polished but still sulphate rich aqueous lithium hydroxide stream 66 is then fed to the Glauber’s salt crystallisation stage 70. Glauber’s salt is sodium sulphate decahydrate.Removal of Sulphate - Glauber’s Salt Crystallisation

[0062] Glauber’s salt is crystallised by cooling in crystallisation stage 70 which, in preferred embodiments, comprises first and second crystallisers. The number of crystallisers may be selected and operated to effectively precipitate sulphate from stream 66 as Glauber’s salt. The first crystalliser operates at a first temperature, preferably lower than 10°C, and the second crystalliser operates at a second temperature lower than the first temperature, preferably -2 to -3°C. However, lower temperatures may be required, possibly down to -10°C. The residence time in the Glauber salt crystallisation stage 70 may vary within a range of 1 to 8 hours (preferably2-6 hours) but, in any event, for a sufficient residence time to enable Glauber’s salt crystallisation.

[0063] The Glauber’s salt crystallisation stage 70 may include a flash unit to optimise energy balance through use of waste heat recovery. A flash unit provides an economic method of reducing the temperature of the filtered caustic solution from filtration unit 65, which may be as hot as 95°C. Therefore, using the latent heat of vaporisation of water to achieve cooling may be used in some embodiments.

[0064] The crystalliser discharge slurry 72 is filtered in filtration stage 75, conveniently using a thickener and a centrifuge or centrifuge only to remove Glauber’s salt solids 77 from the discharge slurry 72. Desirably, the filtration stage 75 is optimised to produce a filtrate in the form of discharge aqueous lithium hydroxide stream 78 containing no more than about 35-40 g / L sulphate for feed to lithium hydroxide crystallisation stage 90.

[0065] The Glauber’s salt solids 77 are dissolved and the resulting solution evaporated in sodium sulphate crystallisation stage 80. Crystallisation stage 80 may include a single crystalliser. Sodium sulphate crystals are separated as a wet cake by filtration, which may be a form of pressure or vacuum filtration, a combination of thickening and centrifuging, or centrifuging only as examples of some embodiments. The solids are then dried in dryer 84 and then packaged for sale in packaging stage 88. Dryer 84 is conveniently a fluid-bed dryer, a rotary dryer, or any alternative dryer used to dry crystalline materials, as is known by practitioners in the field.

[0066] A portion of the aqueous phase 85 from crystallisation stage 80, as may be obtained directly from the crystalliser, or from a thickener overflow or a cyclone overflow is fully or partially fed to the bleed stream unit 210 as shown. Alternatively, stream 85 may be recycled upstream.Lithium Hydroxide Crystallisation

[0067] The sulphate depleted aqueous lithium hydroxide stream 78 is then subjected to magnetic impurity removal in the preferred embodiment by in-line pots before evaporation and evaporative crystallisation in crude lithium hydroxide crystallisation stage 90. Preferably, two crystallisers are 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 threecrystallisers - operating in sequence may be required to achieve the desired LHM purity. Preferred crystallisation temperature range is 70°C to 95°C. More preferred is a crystallisation temperature in the range 70 to 75°C under vacuum. Residence time in crystallisation stage 90 may vary from 30 minutes to 3 hours with the preferred residence time being about 60 minutes.

[0068] The crystallised slurry of crude lithium hydroxide monohydrate (LHM) crystallisation stage 90 contains at least 20 wt% crystals, preferably 30 wt% crystals or higher to facilitate separation. In this embodiment, an aqueous purge 94 is obtained from the crystalliser in unit 90, or from cyclone overflow that thickens the crystalliser discharge slurry. Further separation, in the separation stage 95 of this embodiment, involves dewatering and washing in a centrifuge to produce a wet cake 92, and a filtrate 94b that is returned to causticisation unit 60 in the preferred embodiment. The wet cake 92 is washed at a wash ratio sufficient to remove aqueous impurities, with preferred wash ratio ranging from 0.3 to 2 times the weight of the wet cake 92. The aqueous streams from crystallisation and washing are desirably recycled to other stages of process 1000, in particular those involving processes performed under alkaline conditions such as neutralisation stage 30 or causticisation stage 60. As shown, a portion 94 of the aqueous streams is directed to the bleed stream 210. Clarified aqueous streams may be subjected to magnetic impurity removal using in-line pots.

[0069] In alternative embodiments, depending on the upstream processing efficiency, multiple crystallisers may be arranged in series. Between crystallisers, the lithium hydroxide monohydrate is dissolved in deionised or recycled process water shown as occurring in unit 100 in Figure 1. Therefore, the crude lithium hydroxide monohydrate wet cake 92 is directed to lithium hydroxide dissolution and polishing filtration stage 100 where insoluble particulates are removed from the resultant aqueous lithium hydroxide solution. The polished aqueous lithium hydroxide filtrate from the polishing filter in unit 100 may then be subjected to magnetic impurity removal using in-line pots before being fed to the pure lithium hydroxide crystalliser also in stage 100. Preferred crystallisation temperature range is 70°C to 95°C. More preferred is a crystallisation temperature in the range 70 to 75°C under vacuum. Residence time in crystallisation stage 90 may vary from 30 minutes to 3 hours with the preferred residence time being about 60 minutes.

[0070] In the preferred embodiment, separation stage 105 involves dewatering and washing in a thickener followed by a centrifuge, or just in a centrifuge to produce a wet cake 107 and a filtrate 108 together with a separate wash stream. The wet cake 107 from the terminal (final) crystalliser is washed at a wash ratio sufficient to remove soluble impurities, with preferred wash ratio ranging from 0.5 to 2 times the weight of the wet cake 107.

[0071] The aqueous streams from crystallisation and washing in pure lithium hydroxide crystallisation stage 105, including filtrate 108, are desirably recycled to other stages of process 1000, including crude lithium hydroxide crystallisation stage 90 and those stages involving processes performed under alkaline conditions such as neutralisation stage 30. Clarified aqueous streams may be subjected to magnetic impurity removal using in-line pots.

[0072] Wet cake 107 is directed to drying stage 170 with preferred dryer(s) being a vacuum or plate-type vacuum dryer to preserve crystal integrity. Magnetic impurity removal may be conducted prior to packaging 180 of the dried LHM and dispatched for sale as LHM 190.Bleed

[0073] To allow for steady-state circuit impurity control for process 1000, a bleed stream unit 210 is included to act as a discharge point for the impurities. In one embodiment, the bleed stream unit 210 receives various low to zero lithium containing streams, including filtrate 85, from other process stages as described above. Flash drying may be conducted to produce a dry mixture of salts 246 for sale or disposal, for example in a zero liquor discharge (ZLD) unit such as ZLD unit 240 as known in the art. be utilised to produce anhydrous salts 246 for sale or disposal. Condensate from the ZLD unit 240 may be recycled to the upstream process. For example, in one embodiment, the condensate may be recycled to leach circuit 20 for washing leach residue solids following leaching of the lithium mineral containing feedstock 4.

[0074] In an alternative embodiment, the bleed stream unit 210 comprises a carbonation tank to produce aqueous lithium carbonate upon treatment with sodium carbonate. After filtration using suitable filtration equipment, such as a thickener combined with acentrifuge, the lithium carbonate generated is returned to process stages such as neutralisation stage 30 and / or other impurity removal stages as described above.Lithium Phosphate Precipitation

[0075] In a preferred embodiment, lithium containing liquor 212 from bleed stream unit 210 (and other process liquors such as process washates or process waters) is treated to recover lithium. To this end, lithium containing liquor 212 is first directed to lithium phosphate precipitation stage 220. Phosphoric acid 222 and sodium hydroxide 224 are then added to react with the liquors in mixing tank(s) in the lithium phosphate precipitation stage 220. pH is controlled, preferably to above 10, more preferably to 10.5 or higher. pH 10.5 is preferred. The reaction is preferably conducted at higher than ambient temperature, preferably above 80°C, to precipitate lithium phosphate forming as slurry 226.

[0076] Slurry 226 is filtered in lithium phosphate filtration stage 225, using a suitable filter such as a candle filter or plate and frame filter. Wet lithium phosphate filter cake 228, following washing if desired, is then fed to lithium phosphate degradation stage 230. The filtrate 229 is directed to the ZLD unit 240 for treatment as above described.

[0077] Wet lithium phosphate filter cake 228 is treated with sulphuric acid 232 in lithium phosphate degradation stage 230. Preferred conditions involve treatment with an excess of sulphuric acid, preferably 2.5% excess or greater, at temperature higher than 20°C, preferably 40°C or higher to produce a slurry consisting of lithium sulphate, phosphoric acid, and residual sulphuric acid. Residence time is preferably higher than 30 minutes, more preferably higher than 80 minutes to complete the required process cycle including reaction and cooling of the slurry. The slurry is filtered, for example using a vacuum filter, candle filter or plate and frame filter with the filtrate 234 mainly being phosphoric acid containing some sulphuric acid which may be recycled to lithium phosphate precipitation stage 220.

[0078] The lithium sulphate filter cake 236 may be subjected to a limited wash to displace remnant phosphoric acid with the wash being added to the filtrate 234 recycled to lithium phosphate precipitation stage 220.

[0079] Following any washing, lithium sulphate filter cake is directed to lithium sulphate dissolution stage 250 where it is dissolved using process waters 252 (from elsewhere inprocess 1000) such as condensates, washates or bleeds. The generated lithium sulphate solution 256 may then be returned to upstream units such as evaporation stage 25, neutralisation stage 30 or calcium precipitation unit 40.

[0080] To the Applicant’s knowledge, the process 1000 as described above has a significantly lower greenhouse gas emission footprint compared to current lithium refining facilities. This is achieved at least by:• eliminating the calcination or heat treatment step for lithium containing material in desirable embodiments;• integrating production of sulphuric acid with process 1000; and• recovering and using energy in the leaching and other stages of the process; and

[0081] Those skilled in the art will appreciate that the process for producing a lithium salt as 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.

[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] 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.

[0084] 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 valuesadjacent 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.

Claims

CLAIMS1 . A process for producing a lithium salt by treating a particulate lithium containing material containing lithium bearing minerals comprising: pressure leaching the lithium containing material with concentrated sulphuric acid to form a pregnant solution containing lithium sulphate as a source of lithium for a selected lithium salt for production and impurities; removing the impurities in a series of steps including removal of at least one sulphate compound contained in the pregnant solution, said at least one sulphate compound containing at least one of potassium and sodium; and producing the selected lithium salt following impurity removal.

2. The process of claim 1 , wherein pressure leaching step (a) is conducted in a plurality of pressure vessels or autoclaves, preferably operated in parallel, with particulate lithium bearing material being contacted with pregnant solution.

3. The process of claim 2, wherein said lithium is presented as a slurry to the autoclaves, said slurry comprising the lithium containing material and concentrated sulphuric acid.

4. The process of claim 3, wherein said slurry comprises an additional aqueous stream directed from at least one downstream processing vessel.

5. The process of any one of the preceding claims, wherein pressure leaching step (a) is conducted at temperature above 150°C, more preferably 200°C, preferably below 300°C and most preferably at about 250°C.

6. The process of claim 5, wherein pressure leaching step (a) is carried out with a molar excess of sulphuric acid relative to acid extractable components including multi-valent metal ions, and mineral acid consumers.

7. The process of claim 6, wherein the molar excess of sulphuric acid depends on the lithium containing material composition.

8. The process of claim 7, wherein the lithium containing material is dark mica and the empirically determined optimum acid requirement is 400 kg sulphuric acid per tonne of dark mica.

9. The process of claim 3, wherein a discharge slurry from the autoclave(s) is flash cooled with heat being recovered for preheating said slurry of lithium containing material presented to the autoclave(s).

10. The process of claim 7, wherein a substantial proportion of the at least one sulphate compound separated in step (b) by crystallisation and precipitation.

11. The process of claim 10, wherein said at least one sulphate compound to be separated is dependent on sodium and / or potassium content of the lithium mineral(s) present within the lithium containing material.

12. The process of claim 11 , wherein said at least one sulphate compound containing sodium or potassium contained in said pregnant solution is selected from the group consisting of Glauber’s salt (Na2SO4.10H2O), glauberite (Na2Ca(SO4)2) and glaserite ((K,Na)3Na(SO4)2).

13. The process of claim 12, wherein said pregnant solution contains a plurality of sulphate compounds containing sodium and potassium and said sulphate compounds are precipitated separately by selective crystallisation.

14. The process of claim 11 , wherein separation of said at least one sulphate compound follows a primary impurity removal step comprising neutralisation of the pregnant solution.

15. The process of claim 14, wherein said neutralisation of said pregnant solution comprises causticisation by addition of sodium hydroxide to the pregnant solution.

16. The process of claim 15, wherein sodium hydroxide is added in excess of lithium stoichiometry in the pregnant solution.

17. The process of claim 15, wherein said at least one sulphate compound comprises Glauber’s salt which is separated by crystallisation.

18. The process of claim 17, wherein said crystallisation of Glauber’s salt comprises chilling of the sulphate rich liquor in a series of steps to temperatures from less than 10°C and higher than -15°C.

19. The process of claim 18, wherein said crystallisation of Glauber’s salt comprises two crystallisation stages.

20. The process of claim 19, wherein, in a first crystallisation stage, Glauber’s salt is removed by filtration after crystallisation at 0°C, by filtration; and, in a second crystallisation stage, Glauber’s salt is removed by filtration after crystallisation below 0°C, optionally at -5°C or -10°C.

21. The process of claim 14, wherein said series of steps for removing impurities other than said at least one sulphate compound containing sodium and / or potassium include further steps selected from the group consisting of neutralisation, calcium and magnesium precipitation, ion exchange and crystallisation.

22. The process of claim 21 , wherein said selected series of steps are conducted prior to the removal of said at least one sulphate compound containing sodium and / or potassium.

23. The process of claim 21 , wherein phosphate and fluoride are removed by a neutralisation step for neutralising, optionally by lime or limestone, excess sulphuric acid in the pregnant solution.

24. The process of claim 23, wherein fluoride is removed by reaction of the pregnant solution with phosphoric acid and lime.

25. The process of claim 21 , wherein calcium precipitation, preferably as limestone, is conducted after a prior neutralisation step.

26. The process of any one of claims 21 to 23, wherein said series of steps include an ion exchange step.

27. The process of claim 26, wherein said ion exchange is conducted to decrease the concentration of residual impurities selected from the group consisting of calcium, magnesium, heavy metal ions, boron and fluoride.

28. The process of claim 26 or 27, wherein said ion exchange step comprises a plurality of ion exchange stages.

29. The process of claim 28, wherein said ion exchange step comprises three stages, being:1 ) ion exchange for removal of calcium and heavy metals;2) ion exchange for removal of boron; and3) ion exchange for removal of residual fluoride.

30. The process of claim 29, wherein following ion exchange step 2), the pregnant solution is subjected to acidification.31 . The process of any one of claims 29 or 30, wherein ion exchange step 3) for removal of residual fluoride is conducted before ion exchange step 1 ).

32. The process of claim 29 or 30, wherein ion exchange stage 3) elevates calcium level and pregnant solution from ion exchange stage 3) is directed to a calcium removal stage.

33. The process of claim 32, wherein said calcium removal stage comprises precipitation.

34. The process of any one of the preceding claims, wherein evaporation of said pregnant solution is conducted following leaching step (a) for concentrating lithium sulphate and sulphuric acid and reducing the volume of liquor to be neutralised in a following neutralisation step for primary removal of impurities.

35. The process of claim 34, wherein a portion of the evaporated pregnant solution is recycled to leaching step (a).

36. The process of claim 11 , wherein sulphuric acid production, optionally by sulphur burning, is integrated with leaching step (a).

37. The process of any one of the preceding claims, wherein the lithium containing material is not calcined or otherwise heat treated prior to pressure leaching step a).

38. The process of claim 1 , wherein the lithium containing material is selected from the group consisting of Tun of mine” (ROM) lithium ore, lithium mineral concentrates, lithium containing clays and lithium containing minerals.

39. The process of claim 37, wherein said lithium containing minerals are selected from the group consisting of dark mica, other lithium mica minerals, pegmatite, lepidolite and zinnwaldite, dark mica and other lithium mica minerals, said lithium mica minerals containing - in addition to lithium - elements selected from the group consisting of potassium, rubidium, caesium, fluorine and rare earth elements.

40. The process of claim 39, wherein the lithium containing minerals include dark mica.41 . The process of claim 39 or 40, wherein the selected lithium salt is at least one of lithium hydroxide monohydrate (LHM) or lithium carbonate.

42. The process of claim 1 , wherein, where lithium concentration in the pregnant solution from pressure leaching step a) is less than a threshold, for example in the range 1-10 g / L, the solution is concentrated, preferably by evaporation, to increase lithium concentration by at least one concentration step.

43. The process of claim 42, wherein a primary concentration step is conducted prior to neutralisation and impurity removal.

44. The process of claim 43, wherein a secondary concentration step is conducted downstream of the primary concentration step prior to removing sulphate salts, optionally after an ion exchange stage for removal of impurities.

45. The process of claim 43 or 44, wherein a tertiary concentration step is conducted after the removal of said at least one sulphate compound before a lithium salt is produced.

46. The process of claim 45, wherein said lithium salt is produced by crystallisation in crude form, further crystallisation being conducted to deliver a battery grade product.

47. The process of claim 46, wherein a barren liquor from crystallisation is recycled to an upstream process step.

48. The process of claim 47, wherein said barren liquor contains residual lithium and further processing is conducted to recover a substantial portion of such residual lithium.

49. The process of claim 48, wherein, following delithiation steps, a final brine is directed to a zero liquor discharge unit to produce anhydrous or dry salts.

50. The process of claim 1 , further comprising at least one magnetic impurity removal step.

51. A lithium salt when produced by the process as claimed in any one of the preceding claims.

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