Kinetics of Ammonia Leaching of Multimetal Sulphides

This paper briefly describes the studies carried out on oxidative ammonia leaching of Cu-Zn-Pb multimetal sulphides. Kinetics of zinc and copper dissolution were studied with − 200 + 300 mesh BSS fraction and 1% solids in the slurry. It is observed that the dissolution of sphalerite proceeds by a phase boundary reaction model and that of copper via diffusion through product layer in the temperature range of 70-100°C. The rate equations for zinc and copper dissolution are given by: 1 − (1 − α) 1/3 = k Zn [NH 3 ][pO 2 ] 1/2 1 − 2/3α − (1 2/3α ) 2/3 = k Cu [NH 3 ] 2 [pO 2 ] 1/2 where the symbols have the usual meanings. Activation energies for zinc and copper dissolution reactions are estimated to be 66.5 and 55.4 kJ/mole, respectively. Activation energy values thus obtained are also comparable to those obtained using a differential approach. The leaching results obtained with 10% solids using a wide range of particle size (− 140 + 500 mesh) indicate that copper dissolution is chemically controlled in ammonia as well as ammonia-ammonium sulphate medium in the temperature range of 115-135°C. However, at lower temperature (˜55°C). the leaching reaction follows a diffusion model. Zinc dissolution data show deviations from the shrinking core model due to high extractions in the initial stages.