Amovingboundarymodelunderconsideringthevolumechangeofsphericalresinbeadsduringionexchangeprocesseswasemployedtorecognizethemechanismsofreecoveringuraniumfromcarbonatesolutionsusingstronglybasicanionexchanger.Twoimportantfactors,swellingandionexchange,whichdirectlyaffecttheviolumeofionexchangersweretakenintoaccount.AnionexchangemechanismhasbeenfoundfortheforwardreactionPCl/[UO2(CO3)3]^4-,andisparticaldiffusiongoverningathighconcentrationofthecomplexanion.ThemechanismofRCl/U(VI)atpH5.5-7.5isachemicalreactiontakingplaceatthemovingboundaryoftheunreactednucleus.ForthereversereactionRnU/NaCl,theuranyltricarbonatecomplexanionintheresinphaseisreplacedbyCl^-ionswithanionexchangemechanismalwaydeterminedbyparticlediffusion.TheotherformsofuraniuminthesolidphaseloadedontheresinatpH5.5-7.5shouldbelongtonon-exchangeableuranium.ThemechanismofthereversereactionRnU/HClisalwayschemicalreactionwhichisnotrestrictedtothemovingboundaryoftheunreactedcore.
