Recovery of niobium, titanium and rare earths from Bayan Obo tailings via silicothermic reduction and targeted crystallization

Abstract

The Bayan Obo mine in China has abundant reserves of rare earth, niobium, titanium, iron, and other metal elements. However, due to its low-grade, fine-grained, and heterogeneous mineral characteristics, substantial rare metals are lost in tailings during mineral processing. To achieve efficient separation and enrichment of critical metal from the Bayan Obo tailings, this study applied the silicothermic reduction method to tailings treatment, melting ferroniobium and simultaneously targeted crystallization of the reduced tailings. Thermodynamic analysis and high-temperature simulation experiments showed that in Bayan Obo tailings, iron and niobium were reduced prior to titanium via silicothermic reduction, while rare earth elements were difficult to be reduced. This method achieved the preparation of ferroniobium, with rare earth elements and titanium being targeted enrichment in the slag. By adding CaO to adjust the initial w(CaO)/w(SiO₂) of the tailings to 1.9, a ferroniobium alloy containing 2.02 % niobium could be produced via silicothermic reduction at 1500 °C. The yield of niobium in the alloy can reach 91.01 %, and all rare earth and 98.43 % titanium entered the slag. Following slag-metal separation and prior to slag solidification, the w(CaO)/w(SiO₂) of the slag was adjusted to approximately 1. Prolonged holding at 1100 °C under these conditions facilitated the solid solution of rare earth elements into perovskite and increased the average particle size of perovskite to 44.21 μm, simplifying and coarsening the rare earth-containing mineral phase. Finally, a novel process for treating Bayan Obo tailings was proposed. In contrast to traditional carbothermic methods, this novel approach eliminates CO₂ emissions and carbide precipitation. Furthermore, unlike aluminothermic reduction methods, it exhibits strong selectivity in metal reduction reactions. This method facilitates the targeted crystallization of rare earth elements in the perovskite phase, fostering favorable mineral phase conditions for subsequent flotation-based rare earth extraction.