Promoting effects of CaF2 on the aggregation and growth of metal phases in self-reduction of laterite nickel ore

In view of low-grade laterite nickel ore including high magnesium and silicon, the process of coal-based self-reduction, grinding and magnetic separation is utilized to produce ferronickel powders. The effects of C/O atomic ratio on the self-reduction of iron oxides and nickel oxides are investigated, as well as the influences of CaF2 on the reduction of oxides and the precipitation, aggregation and growth of metal phases in the self-reduction. The results show that under the action of CaF2, the reduction of iron oxides can be suppressed by reducing the C/O atomic ratio to obtain ferronickel powders in high-grade nickel but the recovery rate of nickel will be decreased. The low melting point tremolite(Ca2Mg5(Si4O11)2F2) is generated from the solid-state reaction between CaF2 and silicate gangue with high melting point, which can make the silicate minerals transform from island structure to chain structure, increase the reactivity of silicate minerals and then promote the reduction of nickel oxides and iron oxides. With the addition of CaF2, the melting temperature of laterite nickel ore gangue can be decreased. In that case, the precipitation, aggregation and growth of metal phases can be strengthened in self-reduction and then the separation of metal and gangue can be promoted. Accordingly, the grade of nickel and iron in ferronickel powders and the recovery rate of metal elements are improved significantly.