Separation of impurities aluminum and iron during pressure acid leaching of vanadium from stone coal

During the extraction of vanadium from stone coal by pressure acid leaching, a large amount of aluminum and iron are dissolved along with vanadium, which increases the difficulties of purification and enrichment of the leaching solution. In this study, the separation of aluminum and iron from vanadium has been investigated. It was found that the leaching efficiencies of vanadium, aluminum, and iron reached 90.20%, 30.30%, and 5.73%, respectively, after leaching for 5 h at 190 °C under 2.0 MPa partial pressure of O2 with 15 vol% sulfuric acid solution and 7 wt% potassium sulfate. Potassium sulfate assisted the growth of alunite crystals in the holes and cracks of muscovite particles that had formed since calcium sulfate crystals debonded after interfacial growth. This process strengthened the leaching of vanadium and aluminum from muscovite. Owing to a boost of local concentration of aluminum ions on the addition of potassium sulfate, the precipitation of aluminum ions increased. Meanwhile, ferric ions were precipitated as stable yavapaiite crystals. Thus, an effective separation of aluminum and iron from vanadium could be realized from their mineral source.