The enhancement roles of layered double hydroxide on the reductive immobilization of selenate by nanoscale zero valent iron: Macroscopic and microscopic approaches

Abstract

Herein, we utilized nanoscale zero-valent iron loaded on layered double hydroxide (NZVI/LDH) to immobilize Se(VI) and evaluated the enhancement role of LDH in the NZVI reaction system. The structural characterization indicated that LDH could stabilize and disperse NZVI as well as prevent NZVI from oxidation, thereby increasing iron reactivity. Batch experiments displayed that, compared with those by NZVI, both extent and rate of Se(VI) immobilized by NZVI/LDH significantly increased, owing to the prominent synergistic effect ascribing from adsorption and reduction. Kinetics studies under a series of conditions showed that Se(VI) reaction could be well described by pseudo first-order model. The performance of Se(VI) immobilization was inhibited to a considerable extent by most of co-existing ions, Nevertheless, the presence of Cu²⁺ improved performance of NZVI/LDH due to its role as a catalyst or medium of charge transfer during reduction. XANES revealed that LDH acted as a promoter for complete reduction of Se(VI) into Se(0)/Se(-II) over a wide pH range, whereas EXAFS suggested that LDH acted as a scavenger for insoluble products, making more reactive sites exposure to Se(VI) for reduction. These results suggested that NZVI/LDH as a promising candidate exhibited potential application in remediation of wastewaters containing Se(VI).

Keywords: Enhancement roles; Layered double hydroxide; Nanoscale zero-valent iron; Se(VI) immobilization; X-ray absorption fine structure.