An Oxalic Acid-Mediated Novel Green and Efficient Approach for Vanadium Recovery from Vanadium Slag

Abstract The calcification roasting vanadium extraction process from vanadium slag still faces challenges of relatively low extraction efficiency and discharge of sulfur-bearing tailings, ammonia-nitrogen wastewater, and waste gas. We report an oxalic acid-mediated leaching and vanadium precipitation strategy. Efficient vanadium leaching is attributed to targeted pH regulation, in which oxalic acid provides three driving forces, namely, protonation, precipitation conversion, and complexation. Under optimized leaching conditions of pH 4, 60 min, 60 °C, and a liquid-to-solid ratio of 10 mL/g, the vanadium leaching efficiency reached 99.08%. Leaching kinetic analysis indicated that the vanadium leaching process was jointly controlled by diffusion and chemical reaction, with an apparent activation energy of 15.8 kJ/mol. Subsequently, 99.16% of vanadium in the leachate was recovered as VO2 through oxalic acid-assisted hydrothermal precipitation, and calcination yielded V2O5 with 98.39% purity. Compared with the traditional process, this technology adopts oxalic acid instead of sulfuric acid and ammonium sulfate as leaching and precipitating agents, increasing the vanadium leaching efficiency by approximately 10% under milder conditions. It completely eliminates the discharge of ammonia-nitrogen wastewater and ammonia waste gas generated and produces sulfur-free tailings suitable for blast furnace recycling. This strategy provides a novel route for the efficient and sustainable utilization of vanadium slag.