The use of ion-exchange resins for the recovery of valuable species from slurries of sparingly soluble solids
An example of an industrial process which recovers valuable species by shifting the solid/ liquid dissociation equilibrium condition is the extraction of rare earths from low-grade kaolinite ore by percolation leaching. Valuable species can be recovered from such sparingly soluble solids which slightly dissociate to give traces of the valuable ions in solution, using ion-exchange resins in a slurry mixture. A dissociation equilibrium exists between the dissolved ions in solution and the solid ore. If the dissolved ions are removed from solution by ion-exchange, thus continually displacing the solid/liquid dissociation equilibrium condition, further dissolution of the solid is required according to Le Chatelier's principle so as to restore the equilibrium concentration of the valuable species in solution. It is possible to recover valuable metals from sparingly soluble solids, such as metal sulphates, by contacting a slurry of the solid with an ion-exchange resin. As a result of the ion-exchange that takes place, electrolyte solutions are created which facilitate the dissolution process and hence the overall extraction process by changing the activities of the species in solution. 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 extraction of base metal sulphates was used as a case study.