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The sorption of U(VI), Am(III)/Eu(III) and Cs(I) radionuclides by graphene oxides (GOs) synthesized by Hummers's, Brodie's and Tour's methods was studied through a combination of batch experiments with characterization by microscopic and spectroscopic techniques such as X-ray photoelectron spectroscopy (XPS), attenuated total reflection fourier-transform infrared spectroscopy (ATR-FTIR), high-energy resolution fluorescence detected X-Ray absorption spectroscopy (HERFD-XANES), extended X-ray absorption fine structure (EXAFS) and high resolution transmission electron microscopy (HRTEM). Remarkably different sorption capacity and affinity of radionuclides was found towards GOs synthesized by Hummers's and Brodie's methods reflecting different structure and oxidation state of these materials. Mechanism underlying GO – radionuclide interaction is determined using variety of experimental techniques. For the first time it is shown here that GO - radionuclides interaction takes place on the small holes or vacancy defects in the GO sheets. Mechanism of GO's interaction with radionuclides was analyzed and specific functional groups responsible for this interaction were identified. Therefore, a new strategy to produce improved materials with high capacity for radionuclides suggests the use perforated and highly defected GO with a larger proportion of carboxylic functional groups. Image 1 [ABSTRACT FROM AUTHOR]

In this work, we study different clay samples to examine the effect of structural features of clay minerals (2:1 and 1:1 structures), interlayer cations (Na/Ca/Li forms of montmorillonite), surface area and presence of accessory minerals (iron oxides, calcite, quartz) on Np(V) sorption at trace concentrations. Various techniques, e.g., XRD, XRF, DTG, FTIR, BET absorption and Mossbauer spectroscopy, were used to characterize these clays. The presence of iron oxide as an accessory mineral has a strong effect on Np(V) sorption. Sorption of Np(V) onto different clay minerals with different surface areas, interlayer cations and structures is very similar at a pH range of 4.5–11.5. [ABSTRACT FROM AUTHOR]

Batch sorption experiments on thoroughly characterized bentonites and thermodynamic modeling studies were conducted to reveal the role of iron-containing accessory phases on the interfacial behavior of Np(V). Bentonite clays from different industrial deposits with varying total iron contents were selected for the studies. The samples were characterized by XRD, Mossbauer spectroscopy, XRF, HRTEM, SEM-EDX and other techniques, and wherever possible, the accessory iron phases were identified and quantified. Thermodynamic modeling using available surface complexation data revealed the dominant role of the goethite accessory phase, which was present as nanoparticles, in Np(V) sorption at trace level concentrations (10 −14 M). This fact is independently supported by the combination of SEM-EDX and α-track radiography. These studies illustrate the important role that accessory minerals can play in radionuclides sorption data. This is important to the understanding and modeling of the molecular-level speciation of radionuclides. [ABSTRACT FROM AUTHOR]

237Np isotope is one of the long-lived and hazardous components of the accumulated liquid radioactive waste (LRW). The potential for environmental contamination when the LRW is directly disposed of in deep geological stratum is a matter of concern. Np(V) is highly mobile in the groundwater, and numerous studies are focused on its interaction with natural geological systems and prospective engineered barriers for the radioactive waste repositories. In this work, we studied the neptunium behavior in simulated conditions of acidic liquid radioactive waste injection to the deep permeable stratum collector. To determine components of the host rock preferentially binding the neptunium, and to estimate the effect of elevated temperature on its mobility, a series of laboratory experiments on sorption and leaching of neptunium was carried out using synthetic acid LRW solution and real stratum-collector sand along with individual component simulants. It was found that neptunium sorption on stratum collector sands in the conditions of acidic waste injection is quite low. Clay minerals turned out to be the sorption-dominating components of the host rock for neptunium. Increase in temperature significantly enhances the retention of neptunium on solid phase. Solid-bound neptunium species are sufficiently stable over the two-year experimental time under ambient conditions. [Display omitted] • Neptunium sorption in simulated injection conditions is quite low. • Clay minerals are sorption dominating components of deep stratal bedrock. • Increase in temperature significantly enhances sorption. • Solid-bound at 150°С Np species are sufficiently stable over time even after cooling. [ABSTRACT FROM AUTHOR]

Highlights: [•] TiO2 microspheres different in porosity were synthesized and characterized. [•] Kinetics and pH sorption edges for Am3+/Eu3+ onto TiO2 were studied. [•] The surface stability constants were determined and fitted by LFER. [•] Crystallinity of the sample is determined to be the major factor governing cation sorption. [•] No or small effect of pore size distribution is established on Am3+ sorption. [Copyright &y& Elsevier]

Abstract: It has been recognized that natural aquatic colloids can readily sorb actinide elements, including plutonium, whose behavior is complicated by its multiple valence states and the possibility of redox reactions under environmental conditions. In this paper, the sorption and surface-mediated redox transformations of hexavalent plutonium on synthetic well-characterized hematite colloids are studied in a series of batch sorption experiments. The variation in the kinetics of the Pu–hematite interactions, Pu-L3-XAFS, and HRTEM over a broad range of total concentrations of Pu have been studied in an attempt to define the molecular-level speciation of Pu. The surface-mediated slow reduction of Pu(V/VI) results in the formation of crystalline nanoparticles of PuO2+ x ·nH2O approximately 1.5nm in size at [Pu]tot ⩾10−9 M. This result is confirmed independently by HRTEM images of Pu-containing particles and through the identification in the EXAFS of a Pu neighbor shell at 3.8Å. The formation of such nanoparticles potentially influences the colloid-mediated transport of Pu in the subsurface environment because of the very slow leaching of Pu from the hematite colloids. [Copyright &y& Elsevier]

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]

In the present study, the dissolution and microstructural transformation of CeO 2 nanoparticles (NPs) in a phosphate-containing milieu were investigated. The dissolution behaviour of 2 nm and 5 nm CeO 2 NPs in phosphate buffer solutions was found to differ markedly from that observed in 0.01 M NaClO 4. Through synchrotron X-ray diffraction analysis and X-ray absorption spectroscopy, the interaction between CeO 2 NPs and phosphate species was examined, revealing the transformation of the oxide into sodium-cerium double phosphate, with cerium predominantly existing in the Ce(IV) state. According to scanning and transmission electron microscopy observations, thus formed Na-Ce(IV) phosphate consists of spindle-like aggregates of nanocrystalline rods, presumably formed during phosphate anions sorption on the initial CeO 2 surface. Pair distribution function analysis revealed that Na-Ce(IV) phosphate has a three-dimensional framework crystal structure, similar to NaTh 2 (PO 4) 3 , as reported earlier, with large channels along the c-axis containing disordered sodium atoms. This study represents the first detailed analysis of phosphate-induced speciation and microstructural transformation of CeO 2 NPs, resulting in the formation of Ce(IV) phosphate. Similar processes may occur in natural ecosystems upon the introduction of CeO 2 NPs. [Display omitted] • CeO 2 NPs transform into Na-Ce(IV) phosphate in phosphate buffer. • Transformation rate and dissolved cerium concentration vary with NPs size. • Transformation mechanism involves phosphate sorption and new phase formation on CeO 2 surface. • Na-Ce(IV) phosphate morphology and crystal structure are thoroughly analysed. [ABSTRACT FROM AUTHOR]