Carbonylation of Nickel and Iron from Reduced Oxides and Laterite Ore

Australia has abundant deposits of laterite ores which role in production of nickel is increasing with rising demand for nickel and depletion of sulphide reserves.Laterite ores cannot be efficiently upgraded prior to pyrometallurgical or hydrometallurgical processing what leads to significant challenges in extraction of nickel. The PhD project was undertaken within the ARC (Australian Research Council) Discovery Grant (Project No. DP1094880) which examined a novel approach to processing of laterite ores based on the selective reduction of the ore and extraction of nickel by carbonylation of the selectively reduced ore. Selective reduction of the laterite ore was studied by J. Yang in his PhD project (Yang, 2014). The ultimate aim of this project was to establish the feasibility of extraction of nickel by carbonylation of selectively reduced laterite ore. The project undertook a systematic study of carbonylation of pure nickel and iron, and carbonylation of selectively reduced laterite ore to develop a further understanding of carbonylation reactions and extraction of nickel from laterite ore by carbonylation.Specific objectives of this study included:1) to study the effects of reaction parameters on carbonylation of nickel and iron, including reaction temperature (80-100 °C), carbon monoxide (gauge) pressure (0-56atm), gas flow rate (0.14-0.50 L/min), nickel mass (0.8-3.2g) and particle sizes (0.29 – 2.67 µm), and the effect of sulphur-containing catalysts (sulphur, iron sulphide and hydrogen sulphide);2) to study the non-catalytic and catalytic carbonylation of laterite ores; the impacts of reduction conditions; and effects of reaction parameters;3) to develop further understanding of kinetics and mechanisms of carbonylation processes.Pure metals and nickel-iron mixture were prepared by the reduction of associated oxides by hydrogen at 500 °C (gas flow rate 1.0 L/min); the degree of reduction of oxides was over 98%. Two types of Australian laterite ores supplied by CSIRO were examined (labelled by CSIRO): BCS ore containing 1.35 wt% Ni, 10.4 wt% Fe and 0.038 wt% Co, particle size 53-200 µm; and MIN ore with particle sizes 38-53 µm, 75-90 µm, 140-200 µm, and 355-495 µm, containing 1.68-2.37 wt% Ni, 8.90-11.8 wt% Fe and 0.135-0.144 wt% Co). Selective reduction of laterite ores was conducted by CO-CO2 gas mixture (60 vol% CO) at 750 °C.Carbonylation experiments were conducted in a flexible U – shaped reactor (max pressure 68 atm) immersed into the oil bath. Carbonylation was studied using CO at different pressures. Carbonyls were absorbed by aqua regia in two Dreschel bottles. Samples were taken from the aqua regia solution at different times and analysed by ICP-OES. The extent of carbonylation was calculated using results of the ICP-OES analysis.The non-catalytic carbonylation of nickel at 100 °C and CO pressure 27 atm was close to completion (extent of reaction was 98%) in about 5.5 hours. Carbonylation of pure iron was slow; the extent of iron carbonylation at 100 °C and CO pressure up to 55 atm (gauge) was less than 5.0%. The extent of cobalt carbonylation under these conditions was less than 0.5%.Sulphur containing catalysts accelerated the carbonylation reaction. The time for a complete carbonylation of nickel was shortened from 5.5 hours in the non-catalytic reaction to 2 hours in the catalytic carbonylation at 100 °C and CO pressure 14 atm. The extent of non-catalytic carbonylation of nickel from the selectively reduced BCS laterite ore at 100 °C and CO pressure 41 atm was below 50%. The use of catalysts in the carbonylation of selectively reduced ore was inefficient. The major parameter affecting the rate of ore carbonylation was the particle size. The rate of reaction increased significantly with decreasing particle size; the carbonylation of nickel in MIN ore with the particle size 38-53 and 75-90 µm, was close to completion after 4 hours reaction.Results of a systematic study of the carbonylation of nickel and selectively reduced laterite ores are significant for further understanding of carbonylation reactions. Promising results were obtained for further development of technology of extraction of nickel from laterite ores by the carbonylation process