KINETICS OF DISSOLUTION OF NI3S2 IN ACIDIC POTASSIUM DICHROMATE SOLUTIONS

The dissolution of Ni3S2 in sulphuric acid solutions containing potassium dichromate was investigated. The effect of temperature, dichromate ion concentration, sulphuric acid concentration and particle size has been examined. In addition, the reaction residues at various levels of nickel extraction were examined by SEM, X-ray diffraction, electron microprobe and chemical analysis. Two distinct regions for the dissolution process of Ni3S2 Were observed below and above 50-degrees-C. The leaching at temperatures between 30 and 50-degrees-C is controlled by a product layer diffusion process with an activation energy of 23.9 +/- 3.9 kJ . mol-1. At temperatures above 50-degrees-C the leaching rate was too fast to be measured. The concentration of H2SO4 strongly affects nickel extraction below 0.1 M H2SO4, but at higher concentrations this factor is less important. The dichromate concentration (0.01-0.20 M) has no effect upon the dissolution rate of Ni3S2.