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 V2O5 and vanadium(III, IV) oxides. In the first 2 hr, the release rates of vanadium from V2O3 were r = 1.14 center dot([H+])(0.269) at pH3.0-6.0 and r = 0.016 center dot([H+])(-0.048) at pH6.0-10.0; the release rates from VO2 were r = 0.362 center dot([H+])(0.129) at pH 3.0-6.0 and r = 0.017 center dot([H+])(-0.097) at pH 6.0-10.0; and the release rates from V2O5 were r = 0.131 center dot([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 pH3.8, pH6.0 and pH7.7. The activation energies of vanadium(III, IV and V) oxides (33.4-87.5 kJ/mol) were determined at pH 3.8, pH 6.0 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. (C) 2017 The Research Center for Eco-Environmental Sciences, Chinese Academy of Sciences. Published by Elsevier B.V.