ABSTRACT
Ion exchange resins can be used to recover valuable species from sparingly soluble ores or solid particles that slightly dissociate to give traces of the valuable ions in solution. A dissolution equilibrium is established between the dissolved ions in solution and the solid particles. If the traces of dissolved ions are removed from solution by ion exchange, this equilibrium is displaced so that further dissolution takes place according to Le Chatelier's principle. It is essential that the ion exchange resin has a high equilibrium loading of the valuable species at ultra-low equilibrium concentrations of the solution. The ion exchange resin should also have a high degree of selectivity for the valuable species. Complete dissolution of the sparingly soluble solid, hence complete liberation of the valuable species, can be achieved if a sufficient amount of ion exchanger is present. Improved extraction of the valuable species can be obtained if the associated contaminant species are removed from the solution phase during leaching. Precip-
itation and weak acid formation reactions between the contaminant and the exchanged counter ion, as well as mixtures of cation and anion exchange resins, can be used to reduce the concentration of the contaminants. Enhanced recovery of the valuable species is obtained by increasing the solubility of the solids through the creation of electrolyte solutions from the exchanged counterions initially saturating a mixture of cation and anion exchange resins. The equilibrium relationships for this simultaneous leaching and sorption process are outlined in this chapter. The selective sorption of calcium and magnesium from a sparingly soluble dolomitic ore as well as the recovery of lead from lead sulfate were used as case studies to demonstrate the principles of the process.
