Effective purification of Fe/V as spherical phosphosiderite and porous vanadium oxyhydroxide from waste vanadium-bearing slag

Recovery of valuable vanadium (V) from V-rich waste was of economic and environmental and commonly treated by calcination and/or extraction. Herein, a novel route was developed to stepwise separate Fe and V from grayish slag via a coupled dissolution and hydrothermal route. After dissolving the V-rich slag in acid, the generated leachate was hydrothermally treated with the addition of phosphate and ethanol. 99.1 % Fe was effectively removed, whilst the loss of V and Mg were only 5.2 % and <2 %. The optimal parameters were 160 °C, 20 g/L phosphate and 0.1-ml ethanol. Fe reacted with phosphate and crystallized as phosphosiderite particles at 160 °C. With the Fe removal, free H⁺ was released and then consumed in the redox reaction of nitrate and ethanol. The thermodynamic analysis showed that phosphate accelerated the Fe hydrolysis/crystallization, resulting in the removal of Fe prior to V at the pH < 0.5 and the co-removal of Fe/V at the pH > 1. 98.7 % V was recycled as vanadium oxide hydrate particles by adjusting the leachate to pH 0.2 at 90 °C by adding urea. This provided as a promising strategy to separate Fe and V from leachate and posed potential application in the resource utilization of V-rich waste.