Removal of copper and nickel from concentrated ZnSO4 solutions with silica-supported chelating adsorbents

The removal of copper and nickel from concentrated zinc sulfate solutions using two different silica-supported chelating adsorbents (designated as WP-1 and CuWRAM) was studied. The WP-1 adsorbent contains branched poly(ethyleneimine) anchored on silica and in CuWRAM the anchored polyamine is further functionalized with 2-(aminomethyl)pyridine groups. Binding equilibrium data of sulfuric acid and metal sulfate with these two adsorbents were obtained from batch adsorption measurements. A non-ideal competitive adsorption (NICA) model was used for data correlation. The estimated equilibrium parameters were utilized in a dynamic column model to calculate the break-through curves of mixed metal sulfate solutions. Results of the adsorption column runs show that the selectivity of CuWRAM and WP-1 is sufficient for a feasible separation of copper in the presence of 250-fold zinc excess. Only partial separation of nickel is possible due to the lower uptake selectivity and the very high Zn/Ni feed ratio of 12,000. WP-1 must be used in unprotonated form because of its basicity and fixed-bed operation becomes difficult because of the precipitation of basic metal sulfates. Separation with a protonated adsorbent prevents precipitation but the metal uptake capacity is very low. Due to the lower basicity of the ligand groups of CuWRAM, competitive adsorption of metals is more favorable and similar uptake capacities are attained in acid-form as with unprotonated WP-1. The results of the separation runs are discussed on the basis of equilibrium and kinetic data measured with individual metals. The experimental data are compared with the calculated results and a satisfactory agreement is found for the break-through behavior of copper in CuWRAM and WP-1. (C) 2008 Elsevier B.V. All rights reserved.