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

•nZVI/CNF was successfully synthesized by NaBH4 reduction of Fe3 + in CNF suspension.•The surface precipitation at pH 7.0 was demonstrated by EXAFS analysis.•U(VI) removal on nZVI/CNF was satisfactorily fitted by DLM model at pH < 5.0.

The nZVI/CNF composites were synthesized by borohydride reduction of ferrous salts in the CNF suspension. The characteristic results indicated that metallic Fe0 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 U(IV)O2(s), whereas the EXAFS spectra of U-nZVI/CNF at 2.98 Å 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.

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