SOLUTION PURIFICATION

Separation science and technology, of which solution purification is a part, is a key step in hydrometallurgy, bridging the leaching process with the final metal-winning process. Without the development over the last 30 years or so of the unit processes of solvent extraction and ion exchange and, more recently, of membrane processes, it would have been impossible for hydrometallurgy to have achieved the level of importance it currently holds in extractive metallurgy. Notwithstanding these developments, precipitation processes continue to be of great importance in relation to certain impurity problems such as iron, arsenic, etc.; although the stability of the products of such precipitation processes, in relation to safe disposal, are increasingly coming under scrutiny. Cementation certainly remains a very important purification process. Hydrometallurgical treatment of increasingly complex primary and secondary feeds is also placing more emphasis on solution purification and separation of the values in the leach liquors, thus testing the capabilities of the available unit processes to their limits and presenting researchers and reagent manufacturers with new technical challenges. In this paper, the role and development of solution purification in hydrometallurgy is critically reviewed, current trends and developments highlighted, and future prospects assessed. The growing interest in membrane processes is emphasized. The application of solution purification techniques to effluent and waste treatment is also featured.