Copper removal by chelating adsorption in solution purification of hydrometallurgical zinc production

Use of the chelating adsorbent CuWRAM (R) in the copper removal step of hydrometallurgical zinc process has been studied. This adsorbent contains 2-(aminomethyl)pyridine groups anchored on a polyamine-silica composite and it binds copper and other transition metals by a chelating adsorption mechanism. Equilibrium binding capacity of metal sulfates and sulfuric acid from synthetic and authentic ZnSO(4) process solution was determined at 25-90 degrees C using batch adsorption measurements. The copper removal efficiency was tested using a laboratory-scale fixed-bed column. Results of the equilibrium measurements show that the selectivity of CuWRAM (R) is sufficient for feasible separation of copper in the presence of 250-fold zinc excess. Increasing the operation temperature from 25 degrees C to 60 degrees C affects only slightly the binding capacity of copper and at the same time decreases the capacity of zinc. In column separation, increasing temperature substantially improves copper removal efficiency from the ZnSO(4) process solution. The improvement is mainly due to enhanced intra-particle mass transport. The positive effect is further amplified by marked decrease in viscosity of the feed solution. The optimum temperature for copper removal appears to be around 60 degrees C. According to the results of this study, copper can be separated from the authentic ZnSO(4) solution by the chelating adsorbent, while nickel, cobalt and cadmium must be separated by means of conventional methods like cementation with zinc dust. A process scheme is proposed for the solution purification step in the zinc process. (C) 2010 Elsevier B.V. All rights reserved.