Statistical evaluation and optimization of factors affecting the leaching performance of a sphalerite concentrate

The zinc extraction from a low grade sphalerite concentrate using ferric sulphate and sulfuric acid media was studied and optimized as a potentially promising process for zinc production from low grade zinc resources. The zinc and lead content of the sphalerite concentrate were 32% and 7% and of the original ore 2.8% and 1%, respectively. Six control factors, including reaction temperature, reaction time, pulp density, H2SO4 concentration, Fe3+ ion concentration and particle size, each in five levels were considered using Taguchi technique. L-25 orthogonal array and analysis of variance (ANOVA) were applied to determine the optimum conditions and most significant factors affecting the overall zinc extraction and zinc concentration of leach liquor. The optimum dissolution condition to maximize zinc extraction and zinc concentration simultaneously were T=95 degrees C, t=300 min, D=80 g/l, A=0.5 mol/l, F=1 mol/l, and S=-38 mu m. In verification leaching experiments, zinc extraction and zinc concentration were 71.7% and 23.4 g/l, respectively. These results were in reasonable agreement with the results predicted by the statistical model. In optimum conditions, zinc extraction of 91.5% was obtained after five hours of leaching (which is relatively short time). (C) 2008 Elsevier B.V. All rights reserved.