Decontamination of U(VI) from nZVI/CNF composites investigated by batch, spectroscopic and modeling techniques

The nZVI/CNF composites were synthesized by borohydride reduction of ferrous salts in the CNF suspension. The characteristic results indicated that metallic Fe-0 was uniformly dispersed the surface of CNFs. The decontamination mechanism of U(VI) from nZVI/CNF composites was investigated by batch, XPS, EXAFS and modeling techniques. The batch experiments indicated that removal amount of U(VI) on nZVI/CNF was significantly higher than that of single nZVI, whereas reduction amount of U(VI) to U(IV) on nZVI at pH> 6.0 was significantly higher than that of nZVI/CNF. The EXAFS spectra of U-nZVI at pH 7.0 was similar to the (UO2)-O-(Iv)(s), whereas the EXAFS spectra of U-nZVI/CNF at 2.98 A can be satisfactorily fitted by U-U shell, which was further demonstrated by XANES analysis and surface complexation modeling. The diffuse layer model gave better fits to U(VI) removal on nZVI/CNFs composites, whereas underestimation of U(VI) removal on nZVI was observed at pH > 5.0 due to the presence of reductive precipitation. These findings indicated that nZVI-based composites presented the higher adsorption performance and the excellent reduction capacity for U(VI) under permeable reactive barrier system. (C) 2017 Elsevier B.V. All rights reserved.