Dissolution kinetics of malachite in amm

The leaching of oxide copper ore containing malachite, the unique copper mineral in the ore, was studied using aqueous ammonia solution. The objective was to determine the effect of various parameters on the leaching process, including leaching time, ammonium hydroxide and carbonate concentrations, pH, [NH3]/[NH4+] ratio, stirring speed, solid/liquid ratio, particle size, and temperature. A systematic investigation revealed that the primary factors affecting ammonia leaching of malachite ore were leaching time, the concentration ratio of ammonia/ammonium, pH, solid/liquid ratio, leaching temperature, and particle size. The optimal conditions for effective leaching were identified: ammonia/ammonium carbonate concentrations of 5 M NH4OH and 0.3 M (NH4)2CO3; a solid/liquid ratio of 1:10 g/mL; leaching times of 120 minutes; stirring speed of 300 rpm; leaching temperature of 25°C; and particle size finer than 450 µm. Under these optimized conditions, more than 98% copper recovery was achieved. Additionally, it was determined that during the leaching process, copper dissolved as the Cu(NH3)4+2 complex ion, while gangue minerals remained inert towards ammonia. The study highlighted that interface transfer and diffusion across the product layer were controlling the leaching process, with an activation energy for dissolution calculated at 15 kJ mol/C01.