Reduction of natrojarosite and laterite nickel ore leaching residue composite using palm kernel shell reducing agents at temperatures of 1300-1450℃

Abstract

Lateritic nickel ore processing through hydrometallurgical route generates a significant amount of residue from the leaching stage. Two examples of hydrometallurgical process residues, namely natrojarosite and leaching residue can potentially be used as secondary raw materials for the iron and steel industry. A relatively high sulfur content of up to 12% is a severe issue because the sulfur threshold value for steel raw materials is 1%. Therefore, it is necessary to reduce the sulfur content in natrojarosite and leaching residue to meet the standards as a secondary raw material for the iron and steel industry. In this research, reduction of natrojarosite, laterite nickel ore leaching residue, and palm kernel shell reducing agents composite was conducted in varying amounts of palm kernel shell reductant of 25-100% using a non-isothermal method at an initial temperature of 1000°C with a final temperature of 1300-1450°C and an isothermal method of 1000°C, 1300°C, and 1450°C for 2 hours. The results showed that an excessive amount of reductant (≥25%) would inhibit the formation of iron metal at macrosize (above 0.35 mm). Reduction, both by non-isothermal and isothermal methods, results in decreasing sulfur content in the metal phase as the reduction temperature increases, but a sulfur-rich matte phase is still observed in all experimental conditions. The proportion of the metal phase produced is getting higher and more separated from the slag phase as the temperature increases. The optimum condition was obtained at a non-isothermal reduction of 1450°C using a 25% reducing agent which resulted in iron and sulfur content in the metal phase of 88.53% and 0.49%, respectively, with a metal-matte phase proportion of 65.56%. In this case, slag was dominated by liquid phase with a FeO content of 7.64% and a viscosity of 7.313 PaS.