Extraction of nickel and cobalt from a laterite ore using the carbothermic reduction roasting-ammoniacal leaching process

Abstract

The carbothermic reduction roasting followed by ammoniacal leaching of a Ni-laterite ore from Bajaur (Pakistan) has been studied first time for its potential exploitation via the Caron process. The use of fuel oil as reductant can be costly in Pakistan, therefore, plenty available coal was employed in this study. The roasting parameters like coal mixing proportion (5–15 wt%), temperature (600–900 °C), additive dosage (3–12 wt%), and time (15–180 min) were varied to optimize the selective reduction of Ni and Co. The extent of goethite phase transformation of roasted products characterized through the X-ray diffraction (XRD) analysis could depict sharp peaks for the formation of Ni-Fe alloy phase in the presence of an additive, Na2SO4. The optimal reduction condition was observed to be laterite ore mix with 10 wt% coal and 9 wt% Na2SO4, and roasted at 800 °C for 120 min. Leaching of the roast-reduced product performed in NH4OH–(NH4)2CO3 solutions (150 g/L total NH3) was influenced by carbonate ion concentration and yielded >90% Ni and 67% Co. The apparent activation energy of Ni, 21.2 kJ/mole and Co, 7.6 kJ/mole indicated to follow intermediate-controlled and diffusion-controlled mechanism, respectively. Furthermore, the leach liquor was pre-oxidized and contacted to 10 vol% of LIX 84-I; yielding a selective extraction of >97% Ni over Co at the organic-to-aqueous ratio of 1. Results presented in this paper suggest that the extraction of Ni and Co from Bajaur lateritic ore is technically feasible through the Caron process, and can be useful to others as well.