The extraction of species from slurries of insoluble solids with ion-exchange resins
Insoluble solids which slightly dissociate to give traces of ions in solution can be dissolved with ion-exchangers to recover valuable species. A dissociation equilibrium exists between the dissolved ions in solution and the solid. If the dissolved ions are removed from the solution by ion-exchange, the equilibrium concentration is restored by the further dissociation of the solid. It is possible to recover metals from insoluble solids by contacting a slurry of the solid with an ion-exchange resin which adsorbs the cation, thereby continually displacing the solid/liquid dissociation equilibrium. Complete dissolution of the solid, hence complete liberation of the valuable metal species, can be achieved provided that a sufficient amount of ion exchanger is used. The selective adsorption of calcium and magnesium in dolomite was tested. Various interactions that take place in the slurry during adsorption as well as the effects of various variables, i.e. pH, size of adsorbing species, leaching rates, resins, etc. were determined. A mathematical model for the equilibrium extraction of calcium ions from dolomite was formulated and can be used for possible other applications (rare earths) in the mineral processing industry. © 1995.