Vanadium extraction from V-bearing shale using oxidation roasting and acid leaching

Abstract

Vanadium is an important rare metal element that is extensively used in various fields. Direct acid leaching with fluoride additives and salt roasting-acid leaching are common processes in vanadium production, but they have the disadvantage of high cost and serious pollution to vanadium-bearing shale ore. Therefore, it is necessary to develop an efficient and environmentally friendly process for the development of vanadium-bearing shale resources. In this study, a combination of oxidation roasting (without salt) and acid leaching was used to extract vanadium from V-bearing shale. Pilot scale testwork established the appropriate conditions as a roasting temperature of 870–900 °C, an air atmosphere (O2 concentration of 21 %), a feed rate of 15 kg/h, and a gas flow rate of 34 Nm3/h. The roasted product was leached at an acid dosage of 100 kg of sulfuric acid per ton of roasted product, a temperature of 65 °C, leach time of 4 h, and a liquid/solid ratio of 1.5:1. The pilot plant operation achieved > 85 % vanadium extraction and a vanadium content of < 0.20 % for the leach residue. The phase transformation and microstructure evolution were analyzed using X-ray diffraction, scanning electron microscopy, and surface area and pore size analyses. The results showed that V(III) transformed into V(IV) and V(V) during oxidation roasting, which were easily dissolved by acid leaching. In addition, the pore properties of the roasted products had significant effects on the subsequent leach process. This novel process of oxidation roasting and acid leaching provides an option for vanadium extraction from V-bearing shale.