Optimisation of nickel extraction from laterite ores by high pressure acid leaching with addition of sodium sulphate

Extraction of nickel from Western Australian laterite ores via sulphuric acid leaching at 250 °C has been optimised by the addition of sodium sulphate. Leaching of a nontronitic nickel laterite ore in fresh water, with a sulphuric acid loading of 420 kg/t ore extracted 93% of nickel from the ore. When limonitic nickel laterite ore was leached in fresh water with an acid loading of 310 kg/t ore, 92% of the total nickel was extracted. The nickel extractions were optimised at 96% for the nontronitic ore and 95% for the limonitic ore, at the above acid loadings, when process water sodium ion levels were increased to 4 g/L and 2 g/L, respectively. Further addition of sodium ion resulted in a gradual decrease in overall nickel extraction, as the leach liquor free acidity decreased. At higher acid loadings, the process water sodium ion levels required for optimum extraction were also higher, so as to prevent dissolution of aluminium.