Effect of Sodium Sulfate on Preparation of Ferronickel from Nickel Laterite by Carbothermal Reduction

In this study, the effect of sodium sulfate on preparation of ferronickel from nickel laterite by carbothermal reduction was investigated. The thermodynamic analysis showed that the addition of sodium sulfate can effectively enlarge the region of liquid slag in the phase diagram. The experimental results of carbothermal reduction revealed that sodium sulfate was capable of enhancing the reduction of nickel laterite, as well as promoting the aggregation and growth of nickel-iron particles considerably. Both the size of ferronickel particles and the grade of Ni in the magnetic material increased with increase in the dosage of sodium sulfate. The Ni grade and its recovery ratio were only 2.4 mass% and 58.1% when the raw material was reduced in the absence of sodium sulfate. However, with addition of 8.0 mass% sodium sulfate, the grade of Ni in magnetic material and the recovery of Ni reached up to 9.7 mass% and 89.1%, respectively. The contents of S, P, C and Si in the magnetic materials was also discussed. In addition, the reaction mechanisms of reduction in the presence of sodium sulfate was revealed by investigating the phase transformation, growing character of ferronickel as well as TG and evolved gas analysis. The effective utilization coefficient of nickel (EN) which is a new characterization method of normalization was proposed to compare different studies on preparation of ferronickel from various nickel laterite.