Abstract:According to the empirical equations of potential (φ), pH and the ionic activity factors of various species, the thermodynamics of V-Fe-H₂O system at oxygen partial pressure of 0.5 MPa, ionic activity factor of corresponding concentration of 0.1 mol/kg and temperatures of 60, 100, 150 and 200 ℃ respectively was summarized in the form of (potential—pH) (φ—pH) diagrams. The stable regions of soluble vanadium ions (V³⁺, VO²⁺ and ) contained in the region soluble iron ions (Fe³⁺ and Fe²⁺) at pH＜2. With the increase of temperature from 60 ℃ to 200 ℃, the pH values of stable regions of V³⁺, VO²⁺, , Fe²⁺ and Fe³⁺ become more negative and the redox potentials get higher. The stable regions of vanadium iron spinel and other oxides are substantially less affected. The thermodynamic calculation results indicate that vanadium can be extracted by oxygen pressure acid leaching method, but iron cannot be separated by one-step leaching process. The leachate needs to be purified to make vanadium products. The experiment results show that leaching rates of vanadium and iron are 96.87% and 89.25%, respectively, at temperature of 140 ℃, oxygen partial pressure of 0.5 MPa, particle size ranging between 0.055 mm and 0.075 mm, ratio of liquid to solid (ratio of volume to mass) of 15׃1, leaching time of 120 min, stirring speed of 500 r/min and initial acid concentration of 200 g/L. The experimental results are in good agreement with the results of thermodynamic calculation.

Key words: vanadium-bearing converter slag; oxygen pressure acid leaching; V-Fe-H₂O system; potential—pH diagram