Dissolution kinetics of malachite in amm (1)

The leaching of oxide copper ore containing malachite, the unique copper mineral, by aqueous ammonia solution was investigated. The objective of the study was to determine the effects of various factors such as leaching time, ammonia/ammonium concentration, pH, [NH3]/[NH4+], stirring speed, solid/liquid ratio, particle size, and temperature on the dissolution kinetics of malachite. A comprehensive analysis was conducted to identify the main parameters affecting the ammonia leaching process. Results indicated that optimum leaching conditions included an ammonia concentration of 5 M NH4OH combined with 0.3 M (NH4)2CO3, a solid/liquid ratio of 1:10 g/mL, a leaching time of 120 minutes, a stirring speed of 300 rpm, and a leaching temperature of 25°C, with a particle size finer than 450 µm. The effective recovery of copper exceeded 98%, occurring as the Cu(NH3)4+2 complex ion, while gangue minerals showed no reaction with ammonia. The study concluded that the leaching process was predominantly controlled by interface transfer and diffusion across the product layer, with an activation energy for dissolution determined to be 15 kJ mol/C01.