Kinetic study in selective reduction of limonitic and saprolitic nickel ore: Étude cinétique de la réduction sélective de minerai de nickel limonitique et saprolitique

Saprolite and limonite have different behaviour in the carbothermic reduction process due to the differences in their atomic structures. This work investigates the kinetic study of these two different kinds of lateritic nickel ores. Nickel ore, coal, sodium sulfate, and calcium oxide were mixed, then pelletised into 10–15 mm diameters. The pellets were reduced with a non-isothermal condition using a muffle furnace at 950–1150 °C for 5–120 min. The reduced pellets were crushed into less than 74 µm prior to the wet magnetic separation process to obtain concentrates (ferronickel) and tailings (impurities). The result showed that the reduction rate for both lateritic nickel ores increased with the increase of reduction temperature and holding time. The Ginstling-Brouhnstein model was appropriate to describe the diffusion mechanism of the reduction process of limonite and saprolite. The activation energy in the reduction of limonite was lower than in saprolite. It indicated that the iron and nickel in magnesium silicate in saprolite have lower reducibility than the oxide structure in limonite. Modifying basicity in nickel laterite with CaO addition could also reduce the activation energy.