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.

Most nickel laterite smelting to produce ferronickel is carried out by using an AC-arc furnace. Although the DC-arc furnace is advantageous in smelting fine ore, it is rarely used for nickel laterite. In this work, the effect of slag basicity and stoichiometry of reductant addition in the smelting of low-grade saprolitic nickel ore on nickel grade and recovery, yield, and phases of slag have been investigated clearly. The smelting process was conducted in a laboratory DC-arc furnace with a 30 cm diameter of a single electrode. A 5 kg low-grade saprolitic nickel ore (1.92 Ni-12.97 Fe), some coke as reductant, and some limestone as fluxes were smelted in a DC-arc furnace for about an hour. The pouring temperature of hot metal and slag was 1400-1500°C. The 0.8 of quaternary slag basicity and 0.8 of stoichiometric carbon of reductant resulted in the optimum smelting process of nickel ore in a DC-arc furnace producing ferronickel containing 14.59% Ni grade with 92.26% recovery.