Thermodynamic analysis of selective reduction of nickeliferous limonitic laterite ore by carbon monoxide

The nickel sulphide ore deposits are becoming more expensive to mine, and increasing attention is being paid to the recovery of the nickel from the nickeliferous laterite ore deposits. In contrast to the sulphide ores, these oxide ores cannot be beneficiated by flotation or other conventional mineral processing techniques. One potential concentrating method would be the solid state pyrometallurgical reduction of the ore followed by upgrading using magnetic separation. In this research, a thermodynamic model has been developed in order to investigate the solid state reduction of a nickeliferous limonitic laterite ore by carbon monoxide. The objective was to recover all of the nickel as a high grade ferronickel and convert the goethite (FeO center dot OH) to wustite (FeO), so that the ferronickel could be recovered by subsequent magnetic separation. For the calcined ore, at the stoichiometric carbon monoxide/ore ratio of 0.558 kmol/100 kg, nickel recoveries of similar to 98% and nickel grades of similar to 65% were possible at an optimum reduction temperature of 660 degrees C. The results showed that the nickel recovery and the grade of the ferronickel depended on the reduction temperature and the reductant/ore ratio. For the uncalcined ore, the recoveries were slightly lower and the grades slightly higher due to the increased oxidation potential.