Dissolution kinetics of malachite in ammonia/ammonium sulphate solution

The dissolution kinetics of malachite was investigated in ammonia/ammonium sulphate solution.The effects of ammonia and ammonium sulphate concentration,pH,leaching time,reaction temperature,and particle size were determined.The results show that the optimum leaching conditions for malachite ore with a copper extraction more than 96.8% are ammonia/ammonium concentration 3.0 mol/L NH4OH + 1.5 mol/L(NH4)2SO4,liquid-to-solid ratio 25:1 mL/g,leaching time 120 min,stirring speed 500 r/min,reaction temperature 25 °C and particle size finer than 0.045 mm.The dissolution process of malachite with an activation energy of 26.75 kJ/mol is controlled by the interface transfer and diffusion across the product layer.A semi-empirical rate equation is obtained to describe the leaching process and the reaction orders with respect to concentration of ammonia and ammonium sulphate are 2.983 0 and 0.941 1,respectively.