A novel method for enhancing vanadium extraction from calcified vanadium slag: H2SO4–Na2SO3 synergistic reduction leaching and short process preparation of vanadium dioxide

Abstract

The primary shortcomings of the current vanadium extraction from the calcification vanadium slag process are low vanadium leaching efficiency, potential ammonia pollution risk, and the inability to directly obtain low-valence vanadium products. This research presents an innovative H₂SO₄–Na₂SO₃ synergistically enhanced reduction leaching method that has successfully achieved high-efficiency vanadium extraction. The results indicate that the introduction of Na₂SO₃ enhances the thermodynamic driving force of the acid leaching reaction under low-acidity conditions, makes the reduction of poorly soluble VO₂⁺ to more soluble VO²⁺, promotes the acid leaching reaction, and lays the foundation for the preparation of VO₂ by direct green hydrolysis and precipitation of vanadium from the leachate. Reducing the pH of the leaching system and increasing the Na₂SO₃ dosage are key to improving vanadium leaching efficiency. At a leaching pH of 1.8, with a Na₂SO₃ excess coefficient of 1.5, a leaching duration of 60 min, a liquid-to-solid ratio of 10 : 1 mL g⁻¹, and a leaching temperature of 90 °C, the vanadium leaching efficiency reached 97.01%, reflecting a 10.23% improvement compared to conventional H₂SO₄ leaching. During the hydrolytic precipitation of VO²⁺, a lower precipitation pH enhances the separation of vanadium from impurities in the leachate. Under optimal conditions, precipitation pH of 5, precipitation time of 10 min, and a temperature of 25 °C, VO₂·xH₂O was obtained with a precipitation efficiency of 96.11%. After washing and calcination, VO₂ was obtained with a purity of 98.49%. This innovative reduction leaching process enables efficient vanadium extraction and a streamlined production of low-valence vanadium compounds, while circumventing the environmental concerns associated with conventional ammonium salt precipitation methods.