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Abstract Sorption of U(VI) onto TiO 2 as functions of pH, ionic strength, contact time, soil humic acid (SHA), solid-to-liquid ratio and temperature was studied under ambient conditions using batch and spectroscopic approaches. The sorption of U(VI) on TiO 2 was significantly dependent on pH and ionic strength. The presence of SHA slightly enhanced the sorption of U(VI) on TiO 2 below pH 4.0, while it inhibited U(VI) sorption in the higher pH range. U(VI) sorption on TiO 2 was favored at high temperatures, and the sorption process was estimated to be endothermic and spontaneous. Reduction of U(VI) to lower valent species was confirmed by X-ray photo-electron spectroscopy analysis. It is very interesting to find that U(VI) sorption on TiO 2 was promoted in solutions with higher back-ground electrolyte concentrations. In the presence of U(VI), higher back-ground electrolyte made more TiO 2 particles aggregate through (001) facets, leading more (101) facets to be exposed. Therefore, the reduction of U(VI) was enhanced by the exposed (101) facets and more U(VI) removal was observed. Graphical abstract Unlabelled Image [ABSTRACT FROM AUTHOR]

The interaction behaviors of heavy metals and micaceous minerals are extremely important to understand the environmental behaviors of heavy metals. In this work, the interaction behaviors of Cr(VI) and biotite in the presence and absence of HA were studied combining batch and spectroscopic approaches. Batch experiments showed that biotite had the ability to remove Cr(VI) from the water and the removal markedly increased with decreasing pH. However, sorption of total Cr onto biotite increased with increasing pH (2.0–4.0), whilst quickly decreased above pH ∼ 4.0. It was worth noting that redox process of Cr(VI) to Cr(III), caused by structural Fe(II) on biotite, was another important factor for the high removal of Cr(VI) in a pH range of 2.0–4.0. Ionic strength also influenced Cr(VI) removal that Cr(VI) removal became higher with increasing ion strength. The presence of HA did not show obvious macroscopic effect on Cr(VI) removal, however, HA could cover biotite surface, and promote the sorption of total Cr onto biotite and attenuate the reduction effect caused by Fe(II) on biotite. Spectroscopic approaches, like FT-IR, XRD and XPS further confirmed the existence of Cr(III) on biotite interacting with Cr(VI) and the reduction of Cr(VI) to Cr(III) was drove by the Fe(II) dissolving from biotite to Fe(III). Further, sorption effect and reduction effect competitively contributed to the Cr(VI) removal by biotite, and reduction effect played a more important role at lower pH. [Display omitted] • Biotite removed Cr(VI) from 0% to 100% with pH decreasing from 7.0 to 2.0. • Sorption of total Cr on biotite acted more around pH 4.0. • Cr(VI) reduction caused by structure Fe(II) in biotite increased with the pH decreasing from 4.0 to 2.0. • The presence of HA accelerated Cr(VI) adsorption and attenuated reduction effect. [ABSTRACT FROM AUTHOR]

The regulation effect of Aspergillus niger to the sorption behavior of U(VI) on kaolinite and illite was studied through investigating the enrichment of U(VI) on kaolinite- Aspergillus niger and illite- Aspergillus niger composites. Kaolinite- or illite- A. niger composites were prepared through co-culturation method. Results showed that U(VI) sorption on kaolinite and illite in different pH ranges could be attributed to ion exchange, outer-sphere complexes (OSCs), and inner-sphere complexes (ISCs), while only the ISCs on the bio-composites. Moreover, micro-spectroscopy tests revealed that U(VI) coordinate with phosphate, amide, and carboxyl groups on illite- and kaolinite- A. niger composites. X-ray photoelectron spectroscopy (XPS) further found that U(VI) was partly reduced to non-crystalline U(IV) by A. niger in the bio-composites, occurring as phosphate coordination polymers or biomass-associated monomers. The findings herein provide further insight into the immobilization and migration of uranium in environments. [Display omitted] • Co-culture of A. niger did not change the structures of kaolinite and illite. • U(VI) sorption on kaolinite and illite depended on pH and/or ionic strength. • A. niger changed the sorption mechanism of U(VI) on kaolinite and illite. • U(VI) complexed with various functional groups on the bio-composites. • U(VI) was partly reduced by A. niger to noncrystalline U(IV). [ABSTRACT FROM AUTHOR]

The regulation effect of Aspergillus niger to the sorption behavior of U(VI) on kaolinite and illite was studied through investigating the enrichment of U(VI) on kaolinite- Aspergillus niger and illite- Aspergillus niger composites. Kaolinite- or illite- A. niger composites were prepared through co-culturation method. Results showed that U(VI) sorption on kaolinite and illite in different pH ranges could be attributed to ion exchange, outer-sphere complexes (OSCs), and inner-sphere complexes (ISCs), while only the ISCs on the bio-composites. Moreover, micro-spectroscopy tests revealed that U(VI) coordinate with phosphate, amide, and carboxyl groups on illite- and kaolinite- A. niger composites. X-ray photoelectron spectroscopy (XPS) further found that U(VI) was partly reduced to non-crystalline U(IV) by A. niger in the bio-composites, occurring as phosphate coordination polymers or biomass-associated monomers. The findings herein provide further insight into the immobilization and migration of uranium in environments. [Display omitted] • Co-culture of A. niger did not change the structures of kaolinite and illite. • U(VI) sorption on kaolinite and illite depended on pH and/or ionic strength. • A. niger changed the sorption mechanism of U(VI) on kaolinite and illite. • U(VI) complexed with various functional groups on the bio-composites. • U(VI) was partly reduced by A. niger to noncrystalline U(IV). [ABSTRACT FROM AUTHOR]