Parameters optimization and kinetics of direct atmospheric leaching of Angouran sphalerite

In this research, a zinc sulfide (sphalerite) concentrate of Angouran mine was studied by direct atmospheric leaching process. This process is an alternative to the conventional method of roast-leach-electrowinning (RLE) for zinc production by assisting ferric ions as powerful oxidant. The independent sphalerite leaching parameters investigated were ferric ions concentration (0.4–1.2 M), temperature (40–80 °C), particle size (21–53 μm), sulfuric acid concentration (0.5–1.5 M) and time (2–6 h). Response surface methodology (RSM) was used to optimize the process parameters. The most influencing parameter was found to be temperature and the less effective was acid concentration. Based on the results, ferric ions illustrate a complex effect on the recovery of zinc; In this regard, interaction of ferric ions with operational parameters was proposed. The optimum recovery for leaching of the zinc sulfide concentrate (e.g., 84.72%) was obtained at ferric ions concentration of 1.2 M, temperature of 80 °C, mean particle size of 21 μm and leaching time of 6 h. The predicted percentage recovery of zinc at the optimum condition was found to be 84.96% which was very close to the experimental value of 84.72%. Kinetic investigation was carried out in the optimum condition that obtained by RSM. Kinetic results showed that there were two stages in the sphalerite leaching. At the beginning of the leaching process, kinetics of sphalerite leaching is fast, while after about an hour the overall rate of leaching has decreased. The kinetic of leaching in the first stage is affected by both rate of chemical reaction and rate of diffusion through the sulfur layer. In this stage, the contribution of chemical reaction gradually decreases by increasing the temperature. In the second stage, the leaching rate of sphalerite is controlled only by diffusion through the product layer.