Potential-pH diagrams for V-Fe-H2O system during oxygen pressure acid leaching of vanadium-bearing converter slags.

The thermodynamics were investigated of the V-Fe-H2O system at an oxygen partial pressure of 0.5 MPa, an ionic activity factor equivalent to a concentration of 0.1 mol/kg and temperatures of 60, 100, 150 and 200 degrees C. The potential/pH diagrams showed that stable regions for V(3+) VO(2+) and VO2(+) ions were in the region for Fe(3+) and Fe(2+) ions at pH values less than 2. The pH values of stable regions for V(3+) VO(2+), VO2(+), Fe(3+) and Fe(2+) ions became more negative and the redox potentials increased with increasing temperature. The stable regions for vanadium iron spinel and other oxides were significantly less affected. The calculations showed that V could be extracted using oxygen pressure acid leaching, but Fe could not be separated in a one-step leaching process and purification of the leachate is required to obtain V products. Experimental results showed that V and Fe leaching rates of 96.87% and 89.25% could be obtained at 140 degrees C, oxygen partial pressure of 0.5 MPa, particle size of 0.055-0.075 mm, liquid solid ratio of 15:1 v/w, leaching time of 120 minutes, stirring speed of 500 r/minute and initial acid concentration of 200 g/l. Good agreement was obtained between the thermodynamic calculations and the experimental results.
The thermodynamics were investigated of the V-Fe-H2O system at an oxygen partial pressure of 0.5 MPa, an ionic activity factor equivalent to a concentration of 0.1 mol/kg and temperatures of 60, 100, 150 and 200 degrees C. The potential/pH diagrams showed that stable regions for V(3+) VO(2+) and VO2(+) ions were in the region for Fe(3+) and Fe(2+) ions at pH values less than 2. The pH values of stable regions for V(3+) VO(2+), VO2(+), Fe(3+) and Fe(2+) ions became more negative and the redox potentials increased with increasing temperature. The stable regions for vanadium iron spinel and other oxides were significantly less affected. The calculations showed that V could be extracted using oxygen pressure acid leaching, but Fe could not be separated in a one-step leaching process and purification of the leachate is required to obtain V products. Experimental results showed that V and Fe leaching rates of 96.87% and 89.25% could be obtained at 140 degrees C, oxygen partial pressure of 0.5 MPa, particle size of 0.055-0.075 mm, liquid solid ratio of 15:1 v/w, leaching time of 120 minutes, stirring speed of 500 r/minute and initial acid concentration of 200 g/l. Good agreement was obtained between the thermodynamic calculations and the experimental results.