Enhanced immobilization of ReO4- by nanoscale zerovalent iron supported on layered double hydroxide via an advanced XAFS approach: Implications for TcO4- sequestration

This paper was concentrated on a promising remediation strategy for the reductive immobilization of Tc(VII) by studying its chemical analogue Re(VII) to ease the experimental conditions. A novel composite namely nanoscale zero-valent iron supported on layered double hydroxide (NZVI/LDH) was synthesized and applied for the reductive immobilization of Re(VII). Compared to bare NZVI, the as-synthesized NZVI/LDH exhibited higher efficiency on Re(VII) immobilization due to the good synergistic effect between adsorption and reduction. The precise role of LDH was revealed in detail using an advanced approach. The phrase and morphology analysis indicates that NZVI was uniformly supported on LDH, which apparently reduces the aggregation of NZVI and increases its reactivity. Fe-57 Mossbauer spectra suggest that NZVI/LDH displayed a good anti-oxidation performance, leading to the enhanced stability during reaction. X-ray absorption fine structure (XAFS) results show that LDH could promote complete reduction of Re(VII) into Re(IV) by NZVI, while sorption and reduction occurred simultaneously on bare NZVI. Moreover, LDH not only acts as a pH buffering agents but also as a scavenger for the coexisting anions and sparingly soluble products, which improves the reactivity of NZVI. The excellent immobilization performance of NZVI/LDH provides a promising strategy for decontamination of Tc(VII) from groundwater. (C) 2016 Elsevier B.V. All rights reserved.