Effect of sulfur on the mineral phases of laterite ores at high temperature reduction

Recovery of nickel and cobalt from nickel laterites processed according to the Caron process is hampered by reduction of iron in limonite ores and formation of fosterite in saprolite ores. The Caron process involves the reduction of the ores at temperatures between 700 and 800 °C followed by ammoniacal leaching. The presence of sulfur has been found to markedly improve the Ni and Co recoveries from laterite ores. In this study, limonite and saprolite laterite ores were reduced in the presence of an activator, in the form of elemental sulfur. The mineral phases resulting from the reduction, both in the presence and absence of sulfur were related to recoveries and selectivity obtained from laboratory reduction and leaching tests. The mineral phases were examined using X-ray diffraction with a synchrotron radiation source. The role of sulfur and the history of reduction in effecting the increase in recovery and selectivity of nickel and cobalt was investigated in this study.