Highly selective separation of vanadium over iron from stone coal by oxalic acid leaching

In this paper, a novel method was proposed to selectively extract vanadium from stone coal by oxalic acid leaching. Vanadium was leached, but the iron impurity was maintained in the leaching residue. The effects of leaching conditions on the leaching efficiency of vanadium and iron were investigated for oxalic and sulfuric acid leaching, respectively. For oxalic acid leaching, 71.5% of the vanadium can be recovered with only 3.4% of the iron impurity leached under the leaching conditions: a dosage of H+ of 12 mol/kg, a leaching time of 6 h, a leaching temperature of 368 K (95 degrees C) and a water-mineral ratio of 1.5 L/kg. However, under the same conditions, 74.1% of the vanadium and 13% of the iron were leached during sulfuric acid leaching. The XRD and FTIR analyses showed that both oxalic and sulfuric acid leaching can destroy the crystal lattice structure of muscovite, resulting in the leaching efficiency of vanadium without much difference. Further, the SEM-EDS and XPS analyses indicated that very little pyrite dissolved during oxalic acid leaching, but that much more pyrite dissolved during sulfuric acid leaching. Therefore, oxalic acid leaching can achieve a highly selective separation of vanadium over iron from stone coal. (C) 2016 The Korean Society of Industrial and Engineering Chemistry. Published by Elsevier B.V. All rights reserved.