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5,993,759 34 Thepurificationofnaturalbrinesonlythroughfraction atedcrystalizationhasproventobeacostlyprocessoflow yield,SootheroptionsmustbefoundthataremoreSuitable, especialyforeliminatingboron,magnesiumandcalcium. SUMMARY OF THE INVENTION ItisanobjectofthepresentinventiontoprovideaproceSS forproducinglithiumcarbonatefrombrines. Anotherobjectofthepresentinventionistoprovidea proceSSforproducinglithiumcarbonateofhighpurity. 1O A furtherobjectofthepresentinventionistoprovidea methodforproducinglithiumcarbonatethatiseconomical and efficient. Theseandotherobjectsofthepresentinventionhave15 beenobtainedbyaprocesswhichcomprises: (a)acidifyingabrine,whichcomprisesatleastlithium, magnesium,boronandwater,bymixinganacidthere withsoastomaintainapHofthebrineoffrom0to4 inordertoformboricacid,SaidpHbeingmeasuredby dilutingtheacidifiedbrinewithwaterinaratioof1:10; (b)removingsaidboricacidbycrystalizationtoproduce aboron-depletedbrine; (c)removingboronfromsaidboron-depletedbrineby treatingSaidbrinewithanorganicextractanttothereby 25 produceaboron-freebrine, withlesthan3%ofco-precipitationoflithium.Thisis,in contrasttotheprocessesinwhich,whenprecipitatingthe magnesiumasmagnesiumcarbonatedirectlyfromthecon centratedbrine,10%to25%ofthelithiumcontentis co-precipitated and thus lost. For example, the Chilean patent37,337(1989)ofBrownandBorytaestablishesa process for producing lithium carbonate, which includes precipitatingthemagnesiumandcalcium“byknownchemi calmethods,”withoutSpecifyinganycondition.Ifthe methodsknownfromtheliteraturewereusedforprecipi tating them, especially magnesium, the lithium co-precipitationwould liebetween 20% and 60%. Such a methodisnotcommerciallyaplicable. Theinitialdilutionofthebrineinthepresentinvention furtherprovidesabeterandmoreprecisecontrolofthefinal magnesiumandcalciumcontentinthebrine.Thelithium carbonatethusobtainedisofhighgradewithahighyield andwithaglobalrecoveryoflithiumfromthebrineinthe rangeof80%to90%.Incontrast,theglobalrecoveryin otherprocessesdoesnotreachabove70%.Besidesthis,an importantpartoftheSodiumcarbonatecontainedinthe motherliquorisrecovered. BRIEF DESCRIPTION OF THE DRAWINGS FIG.1showsadiagramofaprocessaccordingtothe presentinvention. DETAILED DESCRIPTION OF THE INVENTION Forabeterdescriptionoftheproces,adetaileddescrip tion thereof wil be made on the basis of a prefered embodiment, which shalhave only an ilustrativeand non-limitingcharacter. Brine 1 of the Salt mine has a typical composition expressedin% byweightasfolows: (d)dilutingsaidboron-frebrinewithamotherliquor; (e) removing magnesium from Said diluted brine by addingSodiumcarbonatetheretoandprecipitatingand Separatingmagnesiumcarbonatetherefromtoforma magnesium-depletedbrine; (f)removingmagnesiumfromSaidmagnesium-depleted brinebyaddingcalciumhydroxidetheretoandprecipi tatingandSeparatingmagnesiumhydroxidetherefrom toformamagnesium-freebrine; (g) adding Sodium carbonate to Said magnesium-free brinetoformandprecipitatelithiumcarbonate;and 35 (h)separatingsaidlithiumcarbonatefromSaidbrineto thereby obtain a lithium carbonate cake and Said 40 mother liquor having a lithium content of 0.1% to 0.3%,byweight. Intheinvention,thebrinesarepurifiedinSequentialform, Sothatthefirstpartoftheboronisremovedascommercial boricacidandthentherestoftheboronisremovedby meansofSolventextractionutilizinganorganicextractant. Thebrinedevoidofboronisthenpurifiedintwostages.In the first stage, the brine is diluted with mother liquor generatedintheprecipitationStageofthelithiumcarbonate, orwithsimilarbrines,precipitatingthenover70%ofthe50 magnesium contained in the brine utilizing a Solution of Sodiumcarbonate(Sodaash),andprecipitatingonlyamini mum quantityoflithiumcarbonatetogetherwiththemag nesium.Therestofthemagnesiumresidueisprecipitatedin asecondpurificationstage,wherecalciumhydroxide(milk55 of lime) is added for precipitating the magnesium as a hydroxide.AnycalciumthatentersintotheSolutionfromthe milkoflimeisprecipitatedascarbonateduetotheSodium carbonate which ispresent in the Solutions. Finaly, the lithium is precipitated warm from the purified brine by 60 addingSodiumcarbonate,obtainingtherebyahigh-quality productwithaminimumofimpuritiesandwithalowcost ofproduction. In the invention, the initial dilution of the brine with motherliquorestablishesafundamentaldiferencewiththe 65 otherexistingproceses,Sinceitallowsaprecipitationof over70%ofthemagnesiuminthefirstpurificationstage Boron Chlorine Magnesium Lithium Sodium Potassium Calcium Sulfate Water 0.5 1.5% 3O 38% 1. 2.5% 5 7% O.O1 O.15% O.O1 O.O2% O.O2 O.05% O.O1 O.O.3% 50 60% 45 Brine1istreatedwithanacidicsolution2ofhydrochloric acid,SulfuricacidorthelikeandisSubjectedtoamixing3 inaSuitableequipment,SuchasaStiredtankorStaticmixer, inSuchawaythattheacidityismaintainedinapHrangeof 0to4.Theacidityismeasuredbydilutingtheacidifiedbrine withwaterinaproportionofbrinetowaterof1to10.The acidificationresultsinprecipitatingboricacidaccordingto thefollowingtypicalreactionsforthecasewherehydro chloricacidisused. Brine 4 treated in this way is allowed to crystalize by coolingattemperaturesof-5to20C.usingSuitable equipmentSuchasathickenerorclarifier5fromwhichthePDF Image | Patent PRODUCTION OF LITHIUM CARBONATE FROM BRINES
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