Effect of CaF2 on the aggregation and growth of ferronickel particles in the self-reduction of Nickel laterite ore

Increasing attention is being paid to the self-reduction and magnetic separation of nickel laterite ore because of economic and efficiency advantages. The aggregation and growth of ferronickel particles during the reduction process is an important factor for subsequent magnetic separation. In this study, the effect of CaF2 on ferronickel particle aggregation and growth during the self-reduction of nickel laterite ore was investigated by visual data analysis of ferronickel particles. The recovery and grade of Ni and Fe from the self-reduction, fine grinding, and magnetic separation of nickel laterite ore under the strengthening action of CaF2 were measured. Increasing CaF2 addition yielded a significant increase in the average particle size of ferronickel particles and an increased recovery of a higher grade of Ni. A ferronickel concentrate with 7.1 wt% Ni and 68.5 wt% Fe was obtained at a Ni recovery of 84.14% in the presence of 8 wt% CaF2. CaF2 accelerates the aggregation and growth of ferronickel particles, which promotes the separation of the ferronickel alloy from the gangue in the magnetic separation process.

Mechanism of Calcium Sulphate on the Aggregation and Growth of Ferronickel Particles in the self-Reduction of Saprolitic Nickel Laterite Ore

Saprolitic nickel laterite is characterized by relatively low iron and nickel contents. Iron and nickel oxides are reduced to form fine ferronickel particles that disperse and embed in silicates in the reduction process, limiting the application of magnetic separation to extract ferronickel. Additives are applied to promote the aggregation and growth of ferronickel particles, then the large ferronickel particles will be separated by fine grinding and recovered via magnetic separation. Calcium sulphate is considered to be capable of increasing the size of ferronickel particles considerably. Due to the decomposition of calcium sulphate in the reduction process, the mechanism of calcium sulphate on the aggregation and growth of ferronickel particles should be conducted studied in-depth. The current work explores the effects of calcium sulphate, elemental sulphur, and calcium oxide on the formation of ferronickel particles in a saprolitic nickel laterite ore. The results showed that the formation of an Fe-FeS eutectic and the mineral structure transformation contributed by calcium oxide were all conducive to the mass transfer of ferronickel particles in gangue, ferronickel particles aggregated and grew up at the boundary between the hole and the gangue. The self-reduction, fine grinding, and magnetic separation of nickel laterite ore in the presence of three types of additive were examined. Nickel laterite ore with 7.88 wt% coal, 12 wt% calcium sulphate reduced at 1200 °C for 30 min, a ferronickel concentrate of Ni 8.08 wt%, and Fe 79.98 wt% was obtained at a nickel and iron recovery of 92.6% and 79.9%, respectively.