The kinetics of chalcopyrite leaching in alkaline glycine/glycinate solutions

Recent research indicated the potential of glycine under alkaline conditions as a lixiviant for copper from its ores and concentrates. In this research, a systematic study has been made of the effects of glycine concentration, temperature, dissolved oxygen, particle size, stirring speed, on the leaching kinetics of chalcopyrite in alkaline glycine from which a power law rate model has been derived to model the shrinking core kinetics. Ultra-fine grinding reduction to 100% passing 10 mu m resulted in an extraordinary improvement in copper dissolution rate and anomalous behaviour compared to changes in rates for larger particle sizes. Kinetic analysis of the two particle size fractions indicated that diffusion through the product layer controlled the leaching kinetics of chalcopyrite at temperatures 40 degrees C and above. At 30 degrees C, chemical reaction contributed in limiting the leaching process, but diffusion through the product layer is dominant. For the 20-38 mu m size fraction, both liquid film diffusion and diffusion through the product layer limited the leaching process although diffusion through the product layer was significantly dominant. Activation energies for the 20-38 mu m size fraction and the ultra-fine size fraction were estimated to be 71.9 kJ/mol and 29.6 kJ/mol respectively. Surface analyses indicated that sulfur is not formed on the leach residue surface and that an iron oxy-hydroxide species was identified on the leach residue. A mixed-rate control shrinking core model is proposed where the rate constant dependence on process variables is given in a power law model form.