Leaching-of-rare-earths-from-bauxite-residue-(red-mud)

Leachingofrareearthsfrombauxiteresidue(redmud)ChennaRaoBorraa,YiannisPontikesb,KoenBinnemansc,TomVanGervena,⇑aDepartmentofChemicalEngineering,KULeuven,3001Leuven,BelgiumbDepartmentofMaterialsEngineering,KULeuven,3001Leuven,BelgiumcDepartmentofChemistry,KULeuven,3001Leuven,BelgiumarticleinfoArticlehistory:Received29July2014Revised5January2015Accepted9January2015AvailableonlinexxxxKeywords:BauxiteresidueLanthanidesLeachingRareearthsRedmudWasteprocessingabstractBauxiteresidue(orredmud)isawastegeneratedduringtheBayerprocessofaluminaproduction.Itsstorageisaspatialandenvironmentalconcern.Currently,therearenobulkapplicationsofbauxiteres-idueexceptforminoruseincementsandceramics.Nonetheless,sometypesofbauxiteresiduesarerichinrare-earthelements(REEs),andtheextractionofscandiuminparticularisofspecialinterest.LeachingexperimentsonGreekbauxiteresiduewereperformedwithdifferentacidsatdifferentconcentrations,liquid-to-solidratios,leachingtimesandtemperatures.ExtractionoftheREEswashighforleachinginHClsolutionscomparedtootheracids,butthedissolutionofironwashighaswell(�60%).ThemaximumextractionoftheREEswasaround80%.Sodiumandcalciumwerecompletelydissolvedduringleaching.Dissolutionofaluminum,siliconandtitaniumwasbetween30%and50%.Theleachingdatashowaverycloseassociationofscandiumwiththeironoxidephases.�2015PublishedbyElsevierLtd.1.IntroductionBauxiteisthemajororeforaluminumproduction.AluminaisextractedfrombauxitebytheBayerprocess.Thewasteslurrygen-eratedinthisprocessiscalledredmudanditssolidfractioniscalledbauxiteresidue.About1–2metrictonnesofbauxiteresidueisgen-eratedforeachtonneofaluminaproduced(Kumaretal.,2006).Theglobalannualgenerationofbauxiteresidueisaround120milliontonnesand2.7billiontonnesofthismaterialhasalreadybeenstockpiled(Klauberetal.,2011).ThepHofthewetredmudslurryisabout12.Itisstoredinhugetailingpondsandthisposesasignif-icantproblem,sinceitnotonlyoccupiesvastlandareas,butitcanalsoleadtoenvironmentalpollution(Poweretal.,2011).Hence,thereisaneedforbettermanagementstrategies