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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., (Copyright © 2021 Elsevier Ltd. All rights reserved.)

The behaviors of U(VI) in environmental media around radioactive waste disposal site are important for safety assessment of geological repositories. However, the estimation of environmental behaviors of U(VI) in natural media was insufficient. This work aimed to determine the adsorption of U(VI) on natural soil surrounding a candidate very low-level radioactive waste (VLLW) disposal site in southwest China. Results showed that the adsorption process of U(VI) on soils could be well supported by pseudo-second-order kinetic and Freundlich model. The adsorption of U(VI) was pH-dependent but temperature-independent. High ionic strength (NaCl) strongly affected the adsorption process at low pH (2.0-5.5). CO 3 2- remarkably inhibited the U(VI) adsorption, while the adsorption of U(VI) was promoted by PO 4 3- and SO 4 2- . Naturally occurred soil organic matters (SOMs) showed high affinity for U(VI), while the presence of additional humic acid (HA) strongly inhibited U(VI) adsorption. The occurrence of ferrous iron could result in the reduction of U(VI) at low pH values (pH < 4), leading to the promotion of immobilization of U(VI). These findings would provide some guidance for the safety assessments of the VLLW disposal as well as the remediation of contaminated soil., (Copyright © 2021 Elsevier Ltd. All rights reserved.)

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 pH4.0, 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., (Copyright © 2018. Published by Elsevier B.V.)

[Display omitted] • A fast reduction of U6+ to U4+ occurs on semiconductors during XPS measurement. • Slower breakage of uranyl occurs on non-semiconductors under X-ray irradiation. • XPS measurement could change the elements state even if far from the center of beam. • Measures are proposed to reduce the beam induced effects in XPS measurement. X-ray photoelectron spectroscopy (XPS) is an efficient technique for recognizing the state of elements. However, the effects of X-ray irradiation on change in the chemical state are sometimes ignored, which may impair the understanding of the environmental behavior of these elements. This study determined the change in the U 4f spectra induced by X-ray irradiation during XPS detection. For U(VI) on non-semiconductors, X-ray irradiation led to a negative shift of U 4f 7/2 to ∼ 380.8 eV due to the break of the uranyl molecules, but not resulting in U(IV) species. However, owing to the photocatalytic reduction of U(VI), the irradiation of U(VI) loaded semiconductors rapidly induced the negative shift of U 4f 7/2 peak to ∼ 379.8 eV, which is the characteristic of U(IV). Moreover, apparent photo-reduction occurred even if the samples were far from the center of the X-ray beam (>3971 μm). Based on these findings, methods for reducing potential error due to X-ray irradiation are suggested, including using the minimum scan time, measuring uranium-containing samples first or independent of other samples, and using X-ray of lower intensity. The results indicated that X-ray induced alteration to the chemical states must be considered when using X-ray techniques. [ABSTRACT FROM AUTHOR]

• Recent progress of heterogeneous U(VI) photoreduction was reviewed for the first time. • The influence of environmental factors on the photocatalytic reduction of U(VI) was discussed. • Photoconversion mechanisms of U(VI) were discussed in detail. • Future perspectives of the photocatalytic U(VI) reduction were presented. The utilization of light-driven heterogeneous photocatalytic technology is extremely appealing for the uranium(VI) reduction since it is promising in seawater uranium extraction and uranium wastes treatment. U(VI) recovery through heterogeneous photocatalysis is more efficient, economic, non-pollutant, and of high selectivity compared to other methods. However, the systematic summarization on U(VI) photocatalytic reduction from water system is indeed scarce, especially, there are several discrepant hypotheses on the photocatalytic process and mechanisms of the reduction of U(VI). Therefore, this review would provide an overview and recent progress in the photocatalytic U(VI) reduction for the first time. The background of the photocatalytic U(VI) reduction is firstly introduced, followed by the discussion of the photocatalytic reduction mechanisms of U(VI). Thereafter, the photocatalysts widely used in the photocatalytic reduction of U(VI) are summarized. Subsequently, the influence of environmental factors such as organic matters, pH, coexisting ions, and dissolved oxygen on the photocatalytic U(VI) reduction is described. Finally, the challenges and the future perspectives of the photocatalytic reduction of U(VI) are addressed. [ABSTRACT FROM AUTHOR]