COMPARISON BETWEEN PURIFICATION PROCESSES FOR ZINC LEACH SOLUTIONS WITH ARSENIC AND ANTIMONY TRIOXIDES

More than 75% of zinc metal in the world is produced by the roast-leach-electrowinning process. In the roast-leach process, very pure zinc sulphate solution must be prepared for zinc electrowinning, because the zinc ion is less noble than the hydrogen ion. Therefore, the purification process is one of the most important unit processes in zinc hydrometallurgy. In general, the cobalt ion is focused on as a typical impurity in zinc electrowinning and several purification processes for cobalt removal have been adopted such as the beta-naphthol process, and the arsenic trioxide or antimony trioxide process. Recently, modernized plants are using the arsenic trioxide or antimony trioxide process, but there are very few published papers on the chemistry of these purification processes. In this paper, firstly the potential-pH diagrams for the systems M-As-H2O and M-Sb-H2O are established for conditions which are close to the operating conditions, and the chemistry of the purification process is deduced from the potential-pH diagrams. Secondly, the phenomena influenced by the chemistry are confirmed experimentally and then a comparison between arsenic and antimony trioxide purification is made based on the experimental results.