THE ROLE OF MIXTURE ADDITIVES ON THE SELECTIVE REDUCTION OF SAPROLITIC NICKEL LATERITE: SODIUM SULFATE - CALCIUM SULFATE

Abstract

High energy consumption and production costs during the metal-slag smelting in the pyrometallurgical process caused many alternative methods to be developed. Selective reduction technology emerges as a potential solution, enabling the processing of nickel laterite into ferronickel concentrate at lower operational temperatures ranging from 1000°C to 1250°C with the presence of some additives. This work investigated the effect of a combination of two additives, i.e. sodium sulfate and calcium sulfate, on the reduction process of saprolitic nickel laterite on nickel and iron grade and recovery in ferronickel concentrate, phase transformation, and the morphology of the resulting ferronickel particles. The saprolitic nickel laterite, coal as a reductant, sodium sulfate and calcium sulfate as additives were mixed and then pelletized into a 10 - 15 mm diameter. The reduction process of pellets was carried out in a muffle furnace from 1050°C to 1250°C for 60 min, and a magnetic separation process was continued to segregate the ferronickel and impurities. Techniques such as XRF, XRD, and SEM-EDS are employed to ascertain the content of nickel and iron, phase changes, and the microstructure of the ferronickel. The study found that the addition of 10 wt. % of the mixture additives, with the composition ratio of 75 : 25 for sodium sulfate and calcium sulfate, at a reduction temperature of 1250°C, generated the optimum of the nickel content and recovery of 17.06 % and 57.01 %, respectively. It also enlarges the particle size of ferronickel up to 26.94 μm. The combination of sodium sulfate and calcium sulfate as additives could enhance the nickel content and recovery in ferronickel by the mechanism of segregating the nickel and iron from the magnesium silicates phase in saprolite and providing the formation of low-melting point phase of troilite promotes the aggregation of ferronickel particle, respectively.