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5,993,759 12 PRODUCTION OF LITHIUM CARBONATE FROM BRINES BACKGROUND OF THE INVENTION 1.FieldoftheInvention Thepresentinventionrelatestoaprocessfortheproduc tionoflithiumcarbonateofhighpurityfromnaturalor artificial brines which contain boron. 2.DescriptionoftheRelatedArts Lithium,thethirdelementinthePeriodicTable,hasan atomicweightof6.939andoccupiesNo.32amongthe elementsoftheearth'scrustwithanaverageconcentration ofonlyapproximately20ppm,whichconfersitthechar acteristicofararemetal.Despitethisfact,lithiumisfound15 distributed in numerous minerals due to itschemical reac tivity.However,thereareveryfewcommercialsourcesfor producinglithium,themainoneofthesebeingthemineral Spodumene,whichisadoublelithium-aluminumSilicate, LiAl(SiO),whichhasatheoreticallithiumcontentof 8.03%.Othermineralswhichareexploitedarepetalite, LiAl(SiOo),whichhasatheoreticalcontentofLiOof 4.88%, and lepidolite, which has a variable composition representedbytheformulaK(LiAl)(SiAl).O(OH,F). ThesetwomineralsareusedmostlyasaditivesinSpecial25 kindsofglassratherthanforobtaininglithium.Another mineralofhighpotentialvalueforobtaininglithiumis hectorite,whichisalowgrademineralwiththecomposition Nao-(Mg,Li)SiOo(OH,F)andwhichisasyetnot exploitedforeconomicreasons,Sinceitslithiumcontent does not exceed 0.5%. OtherSourcesforobtaininglithium,whichhavegrownin importanceinthelasttwodecades,arethebrinesofSalt mines,geysers,andSaltlakes,whereinlithiumcanbefound generalyintheformofchloride,Sulfate,doublepotassium35 andmagnesium,andaslithiumborates.Thelithiumcontent inbrinesvaries,from0.02%asinthebrinesfoundin ClaytonValleyinNev.,USA,to0.2%attheAtacamaSalt MinesinChile.Byevaporationofthebrineandfractionated40 crystalizationoftheSaltscontainedtherein,itisposibleto concentrate the lithium and obtain close to a 6% lithium COntent. hydratedcalciumSulfate.Theprecipitationcontinueswith silvinite(KCINaCl)andafterwardsilvite(KCl).Thelateris aproductforindustrialusesothattowardtheendofthe precipitationoftheSilvite,thebrineistransferedtoanother poolandtheprecipitatedSaltthereofisrecoveredforobtain ingpotassiumchloridebydiferentialfloatation.Continuing afterwardwiththeprecipitationproducescrystalizingof carnalite(KClMgCl26H2O)andthenbishoffite (MgCl26H2O).Inthisstage,thelithiumisincreasedtoabout 4.5%,withamagnesiumcontentofabout4%.Duetothe factthatinthefurtherchemicalpurificationofthebrineitis costlyandcomplextotreatbrineswithhighmagnesium content(about2%),thecrystalizationofthebrinecontinues until5.5%to6%lithiumisobtained.Atthatpoint,the conditionsaresuchthatlithiumcarnalite(LiCIMgCl6HO) isprecipitated,whichdecreasestheoverallithiumrecovery fromthebrine.However,itisposibletolixiviatethe lithiumcarnalitewithfreshbrinetorecoverpartofthe lithiumcontent.Thebrinewithhighlithiumconcentration containsbetween35%to40%ofLiCl,apartfrom1%to4% magnesium,and0.5%to1.5%ofboron,asmagnesium, calcium,andlithiumborates. Thethremainusesforlithiumarecurentlyfoundinthe aluminumelectrowinningindustry,wheretheyareaddedas lithiumchlorideofhighpuritytotheelectrolyteoffused Salts(cryolite);inthehighqualityceramicsindustry,to whichlithiumcarbonateofhighpurityisadded;andinthe productionofmetaliclithium,whereinlithiumchlorideof highpurityisusedasanelectrolytetogetherwithpotassium chloride. Even though itisposible to obtain purified lithium chloridedirectlyfromchlorinebrines,thiswayiscomplex andcostly,anditisusualypreferedtopurifythechlorine brinesandtoprecipitatethelithiumintheformofcarbonate, whichwilthenbetransformedintolithiumchlorideby reactionwithhydrochloricacid.Forexample,Brown, Jacobs,andBoryta(U.S.Pat.No.4,271,131of1981) Suggesttocaryoutanevaporationofthebrinesuntilabout 3% lithiumisobtainedandafterwardtotreatthemwith calciumhydroxideandcalciumchlorideforprecipitatingthe boronashydratedsulfate.However,thelaterstepalso precipitatesaconsiderablepartofthelithiumfromthebrine. The rest of the boron must be eliminated later therefrom, since the process does not remove more than 50% of the Thepresenceofimpuritiesinthelithiumchloridemustbe kepttoaminimum,normallylowerthan0.5%asawhole, particularly Some impurities Such as magnesium and cal ciumwhichcanbeco-precipitatedwiththelithium.Another frequentimpuritythatappearsinnaturalbrinesisboron.In theproductionofmetaliclithiumby theelectrolysisof fusedsalts,theboronmustbeeliminatedbeforethepro ductionofthepurifiedlithiumchloridesince,otherwisethe boronwouldaccumulateintheelectrolyte,thusloweringits conductivitywithaSubsequentdecreaseinproductioncapa bilityofthecels.Thesameoccursinthecelsduringthe electrowinningofaluminum,wherelithiumchlorideis addedtothecryoliteelectrolyteforimprovingitselectric conductivityinSuchawaythatthelithiumcarbonate-from whichthelithiumchlorideisgenerallyobtainedforelectro chemicaluses-mustcomplywithastrictlevelofboron. Therefore, the elimination of impurities from natural brinesrequiresthattheboronberemovedfirst,beforeother impuritiesSuchascalciumormagnesium.Otherwise,the boronlaterprecipitatesalongwiththelithiumcarbonatein theformoflithiumborateorlithiumtetraborate,whichis difficult to eliminate later from the carbonate. Besideslithium,naturalbrinesalsocontainotherele mentslikepotassium,Sodium,calcium,magnesium,iron,45SC. boron, bromine, chlorine, as well as nitrates, chlorides, Sulfates,andcarbonates.Thisrequiresthateachbrinebe treatedinaparticularmanneraccordingtoitscomposition. All brines are concentrated before processing by Solar evaporationtoincreasethelithiumcontentandalsoto50 precipitateotherSaltsthatcouldhavecommercialvaluelike potassium chloride, Sodium chloride, potassium Sulfate, SodiumSulfateorboricacid,aswellasotherdoubleSalts like Silvinite, carnalite, bishofite, Schoenite, kainite, glaserite,glauberite,epSonite,Singenite,etc.Naturalbrines55 arericherinSulfatesandchlorides,especialythelater. ThelargestoftheSaltminesbeingexploitedcurentlyis theAtacamaSaltMineinChile,whichisestimatedto containabout30%ofthetotallithiumcommerciallyexploit ableintheworld.Thissaltminewasfirstevaluatedfor60 commercialexploitationinthe1970s,andthefirstplantto producelithiumcarbonatestartedproductionin1984. ThebrinesarepumpedfromtheSaltmineandare evaporatedinlargeshallowpols,whereaSequentialcrys tallizationofthesaltsisstarted.Sincethebrinesofchlorides 65 aregenerallySaturatedwithSodiumchloride,thefirstSaltto beprecipitatedishalite,orifSulfatesarepresent,haliteandPDF Image | Patent PRODUCTION OF LITHIUM CARBONATE FROM BRINES
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