This work investigated the removal of selenite and selenate from water by sulfate-green rust (GR). Selenite was immobilized by simple adsorption onto GR at pH 8, and by adsorption-reduction at pH 9. Selenate was immobilized by adsorption-reduction to selenite and Se0 at both pH 8 and 9. In the process, GR oxidized to goethite and magnetite. The removal of selenite and selenate by GR was kinetically described through a pseudo-second order model based on inductively-coupled plasma spectrometry (ICP) results. XAFS analysis enabled to elucidate the concentration profiles of Se and Fe species in the solid phase and allowed to distinguish two removal mechanism, namely adsorption and reduction. Selenite and selenate were reduced by GR through homogeneous solid-phase reaction upon adsorption and by heterogeneous reaction at the solid-liquid interface. The selenite reduced through heterogeneous reduction with GR was adsorbed onto GR but not reduced further. The redox reaction between GR and selenite/selenate was kinetically described through an irreversible second order bimolecular reaction model based on XAFS concentration profiles. Although the redox reaction became faster at pH 9, simple adsorption was always the fastest removal mechanism.