Abstract:In order to decrease the evaporating rate of ammonia and increase the solubility of copper in the solution, ethylenediamine was added into the ammonia-ammonium chloride system to leach the copper-containing oxide ores. The thermodynamic model was constructed and the solubility of malachite Cu₂(OH)₂CO₃ in the ammonia-ammonium chloride-ethylenediamine(En)-water system was calculated using the exponential computation method based on both mass balance and charge balance. It is found that the solubility of copper can be increased and the free ammonia concentration can be decreased by submitting partial ammonia with ethylenediamine. The lower free ammonia concentration in the solution is a guarantee to the lower evaporating rate of ammonia. The conditions of malachite Cu₂(OH)₂CO₃ converting to atacamite Cu(OH)_1.5Cl_0.5 were also studied. A group of experiments were designed to validate the veracity of the results of the thermodynamic calculation. It is found that the thermodynamic model is reliable and it can guide the leaching process.

Key words: thermodynamics; solubility; malachite; ammonia; ammonium chloride; ethylenediamine(En)