Direct recovery of low valence vanadium from vanadium slag - Effect of roasting on vanadium leaching

Traditional vanadium products recovered from vanadium slag, such as alloys or battery electrolytes, are manufactured by oxidizing the vanadium to a high valence state (V(V)) and then reducing it to a low valence state again. This process consumes significant energy and raw materials and generates toxic waste water and residue laden with V(V). In this paper, an economic and energy-efficient method to directly extract low valence vanadium (LW) from vanadium slag without producing poisonous waste is proposed for the first time. The structure of the vanadium spinel in the slag was broken by roasting in an O-2 and N-2 atmosphere allowing the low valence vanadium to be leached. Different roasting conditions were studied for their effect on the resulting extraction ratio, showing that after roasting and leaching, low valence vanadium ions in solution accounted for all of the leached vanadium, with an extraction ratio of 69.37%. The products of the roasting process were analyzed by thermal gravimetry, X-ray diffraction, scanning electron microscopy, and X-ray photoelectron spectroscopy. In the vanadium spinels, Fe(II) was oxidized to Fe(III) and V(III) to V(IV), breaking the spinel structure and causing the LW to leach from the vanadium slag.