Removal of soluble uranium by illite supported nanoscale zero-valent iron: electron transfer processes and incorporation mechanisms

Abstract

In this study, natural illite is introduced to support nanoscale zero valent iron (NZVI). The chemical composition and the physical properties of illite supported nanoscale zero valent iron (I-NZVI) are systematically investigated, and I-NZVI is found to significantly reduce the agglomeration of the NZVI particles. A comparison of the U removal capacity between I-NZVI and NZVI over various reaction times is then conducted. With an initial concentration of U at 200 μg/L, the I-NZVI removal capacity of U is as high as 3.41 mg U/g Fe, in contrast to 2.01 mg U/g Fe by NZVI at a dosage of 0.1 g/L. The initial pH of the reaction system determines the U removal capacity of I-NZVI, since it controls the speciation of U and the electron transfer processes during the reaction. Overall, based on the comprehensive understandings of the morphological change, variations in the crystalline structure, and the valence states of U and Fe, the removal mechanisms of U by I-NZVI can be concluded as the following processes: (1) the adsorption and incorporation of U(VI) onto the surface of I-NZVI, (2) the incorporation and reduction of U(V) into Fe(II), and (3) the reduction and precipitation of U(IV) with iron.