Release kinetics of vanadium from vanadium (III, IV and V) oxides: Effect of pH, temperature and oxide dose.

Batch experiments were performed to derive the rate laws for the proton-promoted dissolution of the main vanadium (III, IV and V) oxides at pH 3.1-10.0. The release rates of vanadium are closely related to the aqueous pH, and several obvious differences were observed in the release behavior of vanadium from the dissolution of V2 O5 and vanadium(III, IV) oxides. In the first 2hr, the release rates of vanadium from V2 O3 were r=1.14·([H+ ])0.269 at pH 3.0-6.0 and r=0.016·([H+ ])-0.048 at pH 6.0-10.0; the release rates from VO2 were r=0.362·([H+ ])0.129 at pH 3.0-6.0 and r=0.017·([H+ ])-0.097 at pH 6.0-10.0; and the release rates from V2 O5 were r=0.131·([H+ ])-0.104 at pH 3.1-10.0. The release rates of vanadium from the three oxides increased with increasing temperature, and the effect of temperature was different at pH 3.8, pH 6.0 and pH 7.7. The activation energies of vanadium (III, IV and V) oxides (33.4-87.5kJ/mol) were determined at pH 3.8, pH6.0 and pH 7.7, showing that the release of vanadium from dissolution of vanadium oxides follows a surface-controlled reaction mechanism. The release rates of vanadium increased with increasing vanadium oxides dose, albeit not proportionally. This study, as part of a broader study of the release behavior of vanadium, can help to elucidate the pollution problem of vanadium and to clarify the fate of vanadium in the environment.