Novel Technology for Vanadium and Chromium Extraction with KMnO₄ in an Alkaline Medium

This paper focused on the oxidation–alkaline extraction process of vanadium–chromium–reducing residue. The affected parameters including reaction temperature, KMnO₄ dosage, reaction time, NaOH dosage, and liquid-to-solid ratio on the extraction process were investigated. The E–pH diagram and the thermodynamic analysis indicated that KMnO₄ was suitable for the oxidation of low-valence vanadium and chromium. Vanadium (97.24%) and chromium (56.20%) were extracted under the following optimal reaction conditions: reaction temperature of 90 °C, reaction time of 90 min, dosage of KMnO₄ at m(KMnO₄)/m(residue) = 0.40, dosage of NaOH at m(NaOH)/m(residue) = 0.30, and liquid-to-solid ratio at 5:1 mL/g. The extraction process of vanadium was controlled by the reactant through the solid product layer and the extraction kinetics behavior fitted well with the shrink core model with an E_a of 15.37 kJ/mol. At the same time, the surface chemical reaction was the controlling step for chromium extraction, which was difficult with an E_a of 39.78 kJ/mol.