Mechanistic Insights into Hydrogen Peroxide-Assisted Sulfuric Acid Leaching of Vanadium from Roasted Vanadium-Bearing Ores: A Thermodynamic and Electrochemical Study

Developing efficient technologies for vanadium recovery from refractory raw materials requires an understanding of the thermodynamic and electrochemical behavior of vanadium during acid leaching. This study investigates hydrogen peroxide-assisted sulfuric acid leaching of roasted vanadium-bearing ores from the Greater Karatau region using standard Gibbs free-energy calculations, Pourbaix diagrams, and electrode-potential calculations in HSC Chemistry 8.1.5. The reactions of the model vanadates NaVO₃, Na₃VO₄, and Na₄V₂O₇ with H₂SO₄ exhibited negative ΔG⁰ values at 25 and 65 °C, indicating thermodynamically favorable acid dissolution. The more negative ΔG⁰ values in the presence of H₂O₂ largely reflect the thermodynamic contribution of its decomposition and do not directly quantify its effect on vanadium extraction. Pourbaix diagrams indicated VO₂⁺ as the thermodynamically stable dissolved V(V) species under strongly acidic oxidizing conditions. The higher equilibrium potential of the H₂O₂/H₂O couple relative to VO₂⁺/VO²⁺ indicates the thermodynamic feasibility of oxidizing residual V(IV) to V(V). Competing reactions of Na₂CO₃ with mineral–matrix components may consume the sodium reagent during roasting. The calculations were qualitatively consistent with previously obtained vanadium extraction of 78.70–80.15% from roasted Balasauskandyk and Kurumsak ores at 65 °C. An integrated five-stage physicochemical model is proposed, requiring direct experimental validation of individual stages.