The Role of Limestone in Enhancing Selective Reduction of Nickel in the Carbothermic Reduction of Laterite Nickel

The rarity of sulfide nickel ores has demanded the utilization of nickel extraction processes from alternative sources, namely, laterite nickel. One of the nickel ore processing alternative methods which have less energy consumption is carbothermic reduction. This study aimed to investigate the proper mass composition of limestone flux to get the optimum recovery and grade of nickel and iron, as well as the desirable selectivity factor of the product. The selected limestone mass variations were 8, 9, 10, 11, 12, and 13 wt% of total input materials. The process began with crushing and size classification, dried briquettes formation, making coal–limestone beds according to variations, and carbothermic reduction with pre-heat at 700 °C for 2 h and reduction at 1400 °C for 6 h. After a dry magnetic separation process, series characterization and calculation were conducted, such as energy-dispersive X-ray (EDX), X-ray diffractometer (XRD), recovery calculation, and selectivity factors determination. The highest grade of iron (87.58%) was yielded when using 8 wt% of limestone. While the highest nickel content (18.75%) was obtained when utilizing 11 wt% of limestone. In addition, the highest recovery of nickel and iron was 99.34% (11 wt% of limestone) and 28.91% (8 wt% of limestone), respectively. Furthermore, the highest selectivity factor (9.36) was obtained when utilizing 11 wt% of limestone.