Abstract
In the Caron process, ferronickel produced by reductive roasting of laterite ores is leached in ammonia/ammonium carbonate solution. Thiosulfate ions in the leach liquor, originated from sulfur containing fuels, interfere with the leaching process. A comparative fundamental study of the reaction equilibria, Eh-pH diagrams, and leaching kinetics of Ni, Ni3S 2, NiS, and NiO has been conducted in the presence of different oxidants/anions. Typical Caron conditions were employed in order to examine whether the formation of nickel sulfides/oxide is responsible for incomplete leaching. The relative rates of nickel extraction in the stirred reactors after two hours, decrease in the following order: Ni > Ni3S2 > NiS > NiO. Although Cu(II) and thiosulfate show a synergistic effect to improve the dissolution of metallic nickel, the presence of thiosulfate depresses the dissolution of both nickel sulfides. In the oxygenated Cu(II) leaching system, thiosulfate and hydrosulfide have a beneficial effect on leaching metallic nickel and sulfite has a beneficial effect on both nickel sulfides. Equilibria and relative rates are used to shed more light on possible surface reaction mechanism(s).