New insights into the primary roles of diatomite in the enhanced sequestration of UO22+ by zerovalent iron nanoparticles: An advanced approach utilizing XPS and EXAFS

In the current paper, nanoscale zero-valent iron (NZVI) was immobilized onto the negatively-charged diatomite to obtain a novel composite (NZVI-D) for the enhanced sequestration of uranyl (U(VI)) in water. The as-synthesized NZVI-D was characterized by SEM, TEM and XRD in detail, and better dispersion of NZVI on diatomite surface was observed, as compared with bare NZVI. The efficiency of U(VI) sequestration by NZVI-D was compared with that of commercial iron and bare NZVI. It was found that NZVI-D exhibits the best efficiency in U(VI) sequestration, showing obvious synergistic effect between diatomite adsorption and NZVI reduction. The primary roles were further revealed by complementary macroscopic and spectroscopic studies. XPS results indicated that reduction of highly toxic and mobile UO22+ into less toxic and mobile UO2 could be enhanced using diatomite-supported NZVI. EXAFS analysis demonstrated that diatomite could react as a scavenger for insoluble products like UO2, and thus more reactive sites could be used for U(VI) reduction. Besides, diatomite play multiple roles on pH buffering and preventing NZVI from aggregating and as adsorbent of Fe(II) produced in-situ during reaction for further U(VI) reduction. This study opens a new avenue for the practical application of NZVI and NZVI-D in environmental remediation. (C) 2016 Elsevier B.V. All rights reserved.