An Investigation on the Kinetics and Mechanism of Alkali Reduction of Mine Waste Containing Titaniferous Minerals for the Recovery of Metals

摘要

In a world where declining ore grades are increasingly common, it has become necessary to process low-grade feedstock. Carbothermic reduction in the presence of alkali (Na_2CO_3) has been adapted to beneficiate waste that contains titaniferous minerals (TiO_2 ca. 12 wt%), in order to recover valuable constituents such as TiO_2, Fe and V_2O_5. The waste from vanadium metal processing has environmental legacy as it leaves nearly 1 wt% V_2O_5 process waste, which is environmentally problematic due to V~(5+) ions in contact with water and soil. This investigation focuses on the kinetics and mechanism for alkali reduction of mineral waste bearing 10-12 wt% TiO_2, which we studied in the 1073-1323 K range. The thermogravimetric analysis (TGA) technique was used to record weight loss data. Two distinct regimes demonstrated mixed-control kinetics: (1) at low temperatures the activation energy was found to be 199 kJ mol~(-1), which corresponds to the outward diffusion of O_2~ ions; and (2) at high temperatures the calculated value was 130 kJ mol~(-1), which is consistent with the activation energy for the outward diffusion of Fe~(2+) ions. The metallic iron, sodium titanate and sodium aluminosilicate phases that formed were characterised using X-ray powder diffraction (XPRD) and scanning electron microscopy (SEM) techniques, and their significance for metal recovery is explained.