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Sequential extraction tests were used to study partitioning of U in the bottom sediments of two reservoirs that have been used for the temporary storage of nuclear waste at the "Mining and Chemical Combine" (Zheleznogorsk, Krasnoyarsk region, Russia). Various sequential extraction protocols were applied to the bottom sediment samples and the results compared with those obtained for laboratory-prepared simulated samples with different speciation and partitioning, e.g., U(VI) sorbed onto various inorganic minerals and organic matter, as well as uranium oxides. The distributions of uranium in fractions extracted from simulated and actual contaminated samples were compared to shed light on the speciation of U in the bottom sediments. X-ray absorption spectroscopy, X-ray diffraction, and scanning electron microscopy were also used to analyze the partitioning of U in contaminated sediments. We also compared the results obtained using the spectroscopic and microscopic techniques, as well as sequential extraction. Image 1 • U partitioning in two liquid nuclear waste reservoirs in Russia was studied. • Sequential extraction of samples simulating U forms in environmental objects were investigated. • Four extraction procedures were probed to both model samples and contaminated sediments. • Results of spectroscopic and microscopic methods and sequential extraction were compared. [ABSTRACT FROM AUTHOR]

The sorption of Eu(III) onto montmorillonite samples from different deposits such as those of Kutch (India), 10th Khutor deposit (Russia), and Cortijo de Archidona (Spain) was studied over a wide range of experimental conditions by varying the total Eu concentration, pH, and ionic strength. Various bentonite samples showed quantitative sorption at all pH values at low ionic strengths of the solution because of ion exchange interactions. At a higher ionic strength (1 M NaClO 4), the sorption is pH-dependent because of the interaction with edge sorption sites and it differed from sample to sample. The difference in the mechanism of interaction at different ionic strengths was confirmed by time-resolved laser-induced fluorescence. Thermodynamic modeling was performed with all experimental data for montmorillonite samples from different sources to create a generalized model for describing their interaction with Eu(III). Unlabelled Image • Sorption of Eu(III) onto previously not studied montmorillonite is investigated. • Samples include new Kutch bentonite from India and Khakassia bentonite from Russia. • Admixture iron oxyhydroxide in Kutch bentonite influences Eu(III) sorption. • Thermodynamic model describing Eu(III)–montmorillonite interaction is proposed. • The constant for ion-exchange Eu(III) reaction with montmorillonite is calculated. [ABSTRACT FROM AUTHOR]