Source separation of vanadium over iron from roasted vanadium-bearing shale during acid leaching via ferric fluoride surface coating

The vanadium in acid leachates of vanadium-bearing (V-bearing) shale is usually contaminated by massive impurities during leaching, especially iron impurity. Therefore, the separation of vanadium from iron impurity at source for the production of high purity vanadium products is of great necessity because of increasing demand for vanadium products in the fields of vanadium redox flow battery, specialty steel alloy and catalyst. In this paper, the source separation of vanadium over iron from roasted vanadium-bearing shale during acid leaching was achieved via FeF3 surface coating. Under the conditions of a H2SO4 concentration of 20 vol%, a leaching temperature of 95 degrees C, a leaching time of 4 h and a liquid-solid ratio of 1.5 mL/g, 89.8% of the vanadium leaching efficiency was obtained with only 5.2% of the iron leached with a CaF2 addition of 5 wt%; however, 20.9% of the iron and only 66.2% of the vanadium were leached without CaF2 addition. The enhancement of vanadium leaching efficiency was mainly attributed to the muscovite disintegration in HF generated from the reaction between CaF2 and H2SO4. The suppression of iron leaching behavior was due to the surface passivation of hematite coated with FeF3 which was generated from the reactions of Fe2O3 and FeSO4+ with HF. The FeF3 coating can prevent the attack of H+ and SO42- on the hematite; therefore, the source separation of vanadium over iron during acid leaching was realized. (c) 2018 Elsevier Ltd. All rights reserved.