Reductive atmospheric acid leaching of West Australian smectitic nickel laterite in the presence of sulphur dioxide and copper(II)

Atmospheric acid leaching of West Australian nickeliferous smectite ore was found to be much more effective in the presence of SO2 as a reductant. The rate of leaching was further catalysed by the presence of Cu(II) in solution. The effects of SO2, acid concentration, temperature, particle size and pulp density were examined to optimise the leaching parameters. In the presence of SO2, it was possible to achieve 97% nickel extraction within 10 h leaching with less than 0.1% nickel in the leach residue using 600 kg H2SO4/t of ore with 35% w/w pulp density at 90 °C. The calculated acid consumption was 540 kg/t of dry ore for obtaining > 90% nickel extraction in the presence of Cu(II) catalyst. Cobalt and manganese extractions were very rapid, with most of their extractions within half an hour in SO2–H2SO4 solution. The increase of initial acid concentration, temperature and pulp density increased the metal extraction from the ore, whereas particle size had no effect on the leaching.