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

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 % CaF 2, indicating that the DAL process can selectively extract V from the raw shale. This result was attributed to the passivation of pyrite coated with FeC 2 O 4 ·2H 2 O, 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 % CaF 2 . Moreover, 92.6% of Fe in the roasted shale leachate was removed as FeC 2 O 4 ·2H 2 O 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.