Reduction Kinetics of U(Ⅵ) in Aqueous Solution by Nanoscale Zero-valent Iron

Nanoscale zero-valent iron (nZVI), synthesized in aqueous solution by reduction method, was used to remove U(Ⅵ) from aqueous solution. The effects of pH, nZVI concentration, contact time and temperature on removal of U(Ⅵ) were investigated and the reduction kinetics law on reduction of U(Ⅵ) by nZVI was discussed. The results show that nZVI has very good removal efficiency on U(Ⅵ), and the removal process contains reduction precipitation and sorption. The reduction process follows the pseudo first order reduction kinetics model. The solution pH has evident effect on removal efficiency, and the maximum removal rate reaches 96.27% at pH＝5.0. The temperature has a certain influence on removal efficiency, the apparent rate constant k_obs increases with the temperature, and the relationship between the reduction rate and the reaction temperature accords with Arrhenius law. The reaction activation energy is 16.54 kJ/mol which is below ordinary chemical reaction activation energy (60-250 kJ/mol), which indicates that the reaction is easy to take place.