Physico-chemical characterization and sulphatization roasting of low-grade nickeliferous laterites

Abstract Low-grade nickeliferous laterites from the Sukinda region, Orissa, India, were characterized by microscopic investigations, using X-ray diffraction (XRD), DTA/TG, SEM and IR techniques. The major minerals were goethite, hematite, quartz and chromite. No specific nickel mineral was present. The in situ high-temperature XRD study indicated a structural change of goethite at 300 °C. The DTA/TG and IR data of different laterite samples are discussed in detail. The fixation of nickel in laterite was established by sequential chemical extraction methods. It was observed that more than 50% of nickel was present as lattice substitutions in goethite. Laboratory-scale samples were pugged with sulphuric acid and roasted. The roasted mass was cooled to room temperature and leached with water at 90–95 °C for 30 min at a solid/liquid ratio of 1:10. A mass balance was performed for each experiment, based on total nickel and iron present in the feed, the leach solution and residue. A temperature of 700 °C, 25 wt.% acid and 15 min processing time are found to be most effective for the preferential extraction of around 85% nickel with 2.5% iron.