Pressure acid leaching of sphalerite concentrate. Modeling and optimization by response surface methodology

The zinc leaching from sphalerite concentrate using oxygen under pressure in sulfuric acid solution was primarily studied and evaluated. The effects of important leaching parameters such as oxygen partial pressure, temperature, solid/liquid ratio and leaching time on leaching efficiency, Zn concentration and Fe extraction were investigated. Response surface methodology based on central composite rotatable design technique was used to optimize the leaching process parameters in order to obtain a suitable leach solution with high Zn leaching efficiency considering further processes such as precipitation of contaminating metal ions and electrolysis. The optimum leaching condition for maximum Zn leaching efficiency and Zn concentration with minimum Fe extraction was determined as follows: oxygen partial pressure of 12 bars, temperature of 150 °C, solid/liquid ratio of 0.20 and leaching time of 89.16 minutes. The achieved experimental results for Zn leaching efficiency, Zn concentration and Fe extraction under the optimum conditions were as 94%, 80 g/dm3 and 8.1% respectively. The experimental results corresponded well with the predicted results of quadratic polynomial models.