Eco-Friendly Leaching and Separation of Vanadium over Iron Impurity from Vanadium-Bearing Shale Using Oxalic Acid as a Leachant

Abstract

Oxalic acid, an eco-friendly leachant, was used to selectively separate V over Fe impurity from V-bearing shale in the direct acid leaching (DAL) and blank roasting-acid leaching (BRAL) processes, respectively. For the DAL process, 71.6% of V with only 3.2% of Fe impurity being leached at 95 °C for 6 h with a 1.0 L/kg water–mineral ratio, a 6.0 mol/kg oxalic acid dosage and a 5 wt % CaF2, indicating that the DAL process can selectively extract V from the raw shale. This result was attributed to the passivation of pyrite coated with FeC2O4·2H2O, which can block the reaction between pyrite and oxalic acid. For the BRAL process, 86.8% of V and 35.2% of Fe impurity were recovered after leaching for 4 h at 95 °C with a 1.0 L/kg water–mineral ratio, a 6.0 mol/kg oxalic acid dosage and a 5 wt % CaF2. Moreover, 92.6% of Fe in the roasted shale leachate was removed as FeC2O4·2H2O with only 2.2% of V loss when an Fe powder/Fe(III) molar ratio was 1.25 at 25 °C for 150 min. Therefore, the separation of V over Fe impurity from V-bearing shale using oxalic acid as a leachant is eco-friendly, efficient and sustainable.