Highly efficient oxidative-alkaline-leaching process of vanadium-chromium reducing residue and parameters optimization by response surface methodology

Vanadium-chromium reducing residue was not only a typical solid waste in the steel industry but also a valuable secondary source for recovery of vanadium and chromium. A highly efficient oxidative-alkaline-leaching technology with Na2S2O8 was applied in this work. The effect of experimental factors including m(NaOH)/m(Residue), liquid-to-solid ratio, reaction temperature, m(Na2S2O8)/m(Residue) and reaction time, on the leaching process were investigated. It was showed that 96.3% vanadium was leached out under selected conditions: m(NaOH)/m(Residue) = 0.30, liquid-to-solid ratio of 5 mL/g, reaction time of 60 min, m(Na2S2O8)/m(Residue) = 0.50, reaction temperature of 90 degrees C and stirring rate at 500 rpm, respectively. The leaching kinetics behaviour analysis demonstrated that the controlling step of the reaction was the diffusion of residue through the liquid film, and the Ea for vanadium leaching out was calculated to 15.57 kJ/mol. Response surface methodology was applied to analyze the interaction of the main conditions and the results showed that the influence of experimental factors on the leaching efficiency of vanadium followed the order: m(NaOH)/m(Residue) (B) > m(Na2S2O8)/m(Residue) (C) > reaction temperature (E) > reaction time (D) > liquid-to-solid ratio (A).