Mineral phase reconstruction of Bayan Obo tailings by smelting reduction and crystallization control of molten slag containing niobium, rare earth and titanium

Abstract

Niobium (Nb), rare earth elements (REEs), and titanium (Ti) in Bayan Obo tailings are dispersed across various fine mineral phases. To efficiently recover these valuable elements from Bayan Obo tailings, a novel processing method of complex multimetallic-associated ores, utilizing smelting reduction and crystallization control, is proposed and investigated in this study. First, by observing the crystallization behaviors of CaO-SiO2-La2O3-Nb2O5-TiO2 slag, we observed that Nb and La (lanthanum) were easily dissolved in the perovskite phase that was selected as the target phase for mineral phase reconstruction due to its good flotation characteristics. The effects of w(CaO)/w(SiO2) and the temperature control profile on the crystallization behaviors are discussed in detail. Based on the above investigation, a mineral phase reconstruction experiment performed on Bayan Obo tailings using smelting reduction and crystallization control was carried out. The results indicated that after carbothermic smelting reduction at 1,600 °C, the iron oxides in the tailings were selectively reduced to molten iron that could settle separately from the molten slag, while Nb, REEs, and Ti were enriched in the slag. After temperature-controlled crystallization of the molten slag, 94 % of the Nb and 63 % of the REEs precipitated in the perovskite, and this created a good mineral phase for the efficient flotation of Nb, REEs, and Ti. Finally, a novel processing method for Bayan Obo tailings is proposed after a feasibility analysis of reactor selection, product value, energy consumption, and eco-friendliness.