The catalytic action of cupric and ferric ions in nitric acid leaching of Ni 3S 2

Abstract

The kinetics of dissolution of synthetic Ni 3S 2 in nitric acid solution containing ⩽ 2.0 M HNO 3 in the presence of cupric and ferric ions was investigated. The effects of stirring, particle size, temperature and concentration of cupric and ferric ions were examined. Solid residues at various levels of nickel extraction were examined by SEM, X-ray diffraction, electron microprobe and chemical analysis. The constant dissolution rate of Ni 3S 2 was attributed to the electrochemical reaction occurring on the surface of flat-plate type Ni 3S 2 particles. The reaction kinetics were found to be independent of both cupric and ferric ion concentrations up to 1 m M. Cupric ion did not act as a catalyst at temperatures below 60°C. At 80°C cupric and ferric ions show the same catalytic activity. The activation energy in the presence of ferric ions was 103.6 ± 4.2 kJ/mol. A mechanism for Ni 3S 2 dissolution in the presence of cupric and ferric ions is proposed.