Thermodynamic Modeling of Phase Formation Conditions in the CuO–CO2–H2O–NH3 System

Phase formation in the CuO–CO2–H2O–NH3 system was studied using thermodynamic modeling in the temperature range 25–100°C, at рo = 0.1 MPa, and at aqueous ammonia concentrations of 0, 0.01, and 2.0 mol/kg. The stability fields of tenorite (Tnr) [CuO], malachite (Mlc) [Cu2CO3(OH)2], and azurite (Azu) [Cu3(CO3)2(OH)2] were determined, and the compositions of the solutions in equilibrium with solid phases were calculated. The effects of temperature and ammonia concentration on phase relations in the system were shown. Upon exposure of tenorite, malachite, and azurite to 1.0–3.0 mol/kg aqueous ammonia solutions, the copper concentration in the solution increased as ammonia concentration increased, and decreased as temperature increased. The results presented in this paper provide a basis for understanding the mineral formation scheme in aqueous copper–carbonate systems, as well as for solving a number of environmental problems and developing ammonia leaching technologies.