•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.Download high-res image (268KB)Download full-size image

•The Fe3O4/FA was prepared and used for Ni(II) removal.•The Fe3O4/FA showed higher Ni(II) removal than bare Fe3O4 did.•The Fe3O4/FA showed good reusability for Ni(II) removal.•Fe3O4/FA could be easily recovered from water using a magnet.Recently, magnetic nano-materials have attracted great attention as effective and potential adsorbents for the fast sequestration and quick separation of contaminants in the real work of wastewater treatment. In the present work, fulvic acid (FA) decorated Fe3O4 (Fe3O4/FA) magnetic nanocomposites were developed for the sequestration of Ni(II) by an adsorption process from a synthetic wastewater. The results indicated that the surface-coated FA improves the dispersion of Fe3O4/FA and promotes the removal performance of Fe3O4/FA towards Ni(II). The retention of Ni(II) onto Fe3O4/FA obtained adsorption equilibrium in less than 2 h, and could be well described by the Langmuir adsorption model. The adsorption of Ni(II) onto Fe3O4/FA was strongly pH-dependent and ionic strength-independent, and so the inner-sphere surface complexation is the main mechanism responsible for the uptake of Ni(II) onto Fe3O4/FA. The Fe3O4/FA magnetic composites were able to remove ~ 95.0% of Ni(II) from an aqueous solution at optimized pH. The Fe3O4/FA also showed good regeneration and separation convenience for the treatment of simulated Ni(II)-bearing effluent. Considering the low-priced and environmental friendly properties, we can see that FA could be easily coated on magnetic nanocomposites to form novel nanocomposites by a simple co-precipitation procedure for the development of a new environmental remediation method and to find the application potential of these magnetic nanocomposites in environmental fields.