Adsorption-reduction strategy of U(VI) on NZVI-supported zeolite composites via batch, visual and XPS techniques

Nanoscale zero valent iron (NZVI) modified MCM zeolite composites (NZVI/MCM) were obtained by reduction and in-situ growth process, and were characterized by SEM, TEM, XRD, HRTEM, TEM-EDS, and XPS techniques. Investigation results showed that the surface of NZVI/MCM were coated with NZVI particles mainly in the range of 10–100 nm, and only part of NZVI particles > 100 nm or <10 nm. The synthesized composites were applied as adsorbents for U(VI) removal from aqueous solutions. The maximum U(VI) removal capacity on NZVI/MCM was calculated to be 216 mg/g at pH = 5.6 and T = 298 K. Further advanced spectroscopy analysis showed that U(VI) adsorption and reduction could be enhanced by NZVI/MCM due to the synergistic effect between NZVI and MCM. Meanwhile, the adsorption of U(VI) was related with the surface functional groups (e.g., –OH, Fe-O and Si-O functional groups) and the reduction of U(VI) to U(IV) was ascribed to the oxidation of Fe0 and Fe(II) on the core–shell of NZVI. The results were helpful for the simultaneous adsorption-reduction of U(VI) on the composites. This work highlights the adsorption-reduction-solidification strategy for the elimination of U(VI) in wastewater cleanup.