Development of a Low-Temperature Bloomery Process for Nickel and Cobalt Recovery from Saprolite Ores

Abstract

The bloomery process in rotary kilns is used for reducing roasting of high-magnesia saprolite ores at relatively low temperatures (1200–1225°C). The influence of flux (limestone, bauxite, fluorite) and sulfur-containing (pyrite concentrate, elementary sulfur, gypsum) additives on the temperature of coarsening of metallic particles with the formation of coarse ferronickel grains is studied at a reducing roasting time of 30 min. The optimum charge composition is determined, and the simultaneous introduction of 2–3% CaF2 and 0.8–1.2% (based on sulfur) sulfur-containing additive into a charge at the optimum limestone and bauxite additives is shown to decrease the temperature of coarsening of metallic particles to 1200–1225°C. In this case, aggregates of metallic ferronickel grains bound by a sulfide phase form. According to electron-probe microanalysis data, 90–92% nickel concentrate in a metallic phase, 4–5% concentrate in a sulfide phase, and 4–6% nickel is retained in a slag. The accumulation of a sulfide phase as a binder between metallic grains and the presence of magnetic properties in both phases substantially facilitate their extraction into a magnetic phase during separation with high indices of nickel and cobalt recovery. The formation of metallic grain aggregates and a sulfide phase create favorable conditions for further processing of the magnetic product by high-pressure sulfuric acid leaching or a carbonyl method to produce called-for products (nickel sulfate, high-purity metallic powders).