Reductive removal of Se(IV) by nanoscale zero-valent iron under anoxic conditions: Kinetics and mechanism

Nano-zero valent iron (NZVI) was employed to remove Se(IV) from groundwater. The kinetics of Se(IV) removal by NZVI as functions of pH, initial selenite concentration and reaction temperature were investigated and the reaction products of Se(IV) with NZVI were determined with X-ray Absorption Near Edge Structure Spectroscopy (XANES). The results demonstrated that the Se(IV) could be rapidly removed by NZVI with pseudo first order reaction rate constants decreasing from 0.339 to 0.149 min^-1 as pH increased from 4.0 to 7.0. Moreover, the removal rates of Se(IV) by NZVI at pH 6.0 dropped with elevating initial Se(IV) concentration. The activation energy of Se(IV) removal by NZVI was determined to be 26.26 kJ·mol^-1. The XANES analysis unraveled that Se(IV) was removed by NZVI via adsorption followed by reduction to Se(0).