Fractionation Studies to Increase the Ni Grade of Saprolite Ores from the Wolo Mine Area, Kolaka Regency of Southeast Sulawesi, Indonesia

The raw materials of stainless steel production are mainly derived from nickel laterite ore. The production of stainless steel is carried out using the pyrometallurgical method. The Rotary Kiln Electric Furnace (RKEF) process is widely used to produce ferronickel or nickel matte. The feed for the RKEF smelter originates from saprolite ores and is usually divided into soft saprolite and rocky saprolite. Soft saprolite generally has a higher Ni-grade than rocky saprolite. The potential for increased nickel grade in rocky saprolite can be carried out by screening the bulk ores to minimize gangue materials. In this study, a total of 22 samples of saprolite ore were taken from five different mining fronts and then screened to produce a series of fractions with the size of -2", +2"-4", +4"-6", +6"-8", + 8”. Results of chemical analysis using the XRF method show that enrichment of Ni was found in the -2” fractions, and Ni grade tends to decrease with the larger fraction sizes. Lizardite is the principal nickel-hosted mineral in saprolite ores with the highest composition in the cumulative fraction -2”. Gangue minerals, mainly olivine, significantly affect the enrichment of Ni, especially in the coarser fraction. The higher olivine composition indicates a lower Ni content. The (+6-8)" and (+8)" fractions should be removed to obtain the optimum Ni grade and recovery.