Anna Yu. Romanchuk

Plutonium sorption onto hematite colloids at femto- and nanomolar concentrations

Abstract The surface-mediated reduction of Pu(VI) upon sorption onto hematite colloids is addressed in the paper that bring some new light on the mechanisms of interaction of Pu in high valence states with different Fe(III) oxides. We study the sorption of Pu taken at two different total concentrations around 10−9 and 10−14 M using 239Pu and short-lived 237Pu tracer. In order to conclude on the mechanisms of Pu sorption onto hematite, the kinetics of sorption of Pu(IV) and Pu(VI) at two concenrations is studied as well as its leching behavior. The rate limiting step in Pu(VI) sorption is its surface-mediated reduction. The experimental evidence of the polymerization of Pu(IV) on the surface taken at Pu total concentration of ∼10−9 M is presented based on the kinetics of sorption and leaching behavior.

Origin of long-range orientational pore ordering in anodic films on aluminium

Porous anodic aluminium oxide has a long history of practical application for corrosion protection and coloring. In the last few decades a lot of hi-tech applications of this material have been found owing to the discovery of anodization conditions leading to the formation of highly ordered porous structures with a narrow pore size distribution. Here we show that in-plane orientation of the porous system in anodic films on aluminium is fully determined by the intrinsic crystallographic orientation of the Al substrate. The anisotropy of aluminium oxidation rates on a scalloped metal–oxide interface leads to reorientation of Al spikes in certain directions, which builds up an in-plane orientational order on a macroscopic scale restricted by a crystallite size. This is a unique example of the inheritance of the substrate crystal structure by an amorphous film through a size difference of three orders of magnitude.

Actinides sorption onto hematite: experimental data, surface complexation modeling and linear free energy relationship

Abstract The sorption of actinides in different valence states – Am(III), Th(IV), Np(V) and U(VI) onto hematite have been revisited with the special emphasis on the equilibrium constants of formation of surface species. The experimental sorption data have been treated using surface complexation modeling from which the set of new values of equilibrium constants were obtained. Formation of inner sphere monodentate surface species adequately describes the pH-sorption edges for actinide ions indicative the ionic electrostatic nature of bonding with small or no covalency contribution. The linear free energy relationship representing the correlation between the hydrolysis constants and surface complexation constants has been developed for various cations including K(I), Li(I), Na(I), Ag(I), Tl(I), Sr(II), Cu(II), Co(II), La(III), Eu(III), Ga(III), Am(III), Th(IV), Np(V), U(VI).

Cs(I) and Sr(II) Sorption onto Graphene Oxide

ABSTRACT This article demonstrates the efficacy of graphene oxide (GO) for Cs(I) and Sr(II) removal from aqueous solutions in the presence of competing cations. The interaction mechanisms of Cs(I) and Sr(II) with GO were studied at varying pHs, ionic strengths, and solution compositions. Thermal treatment was studied as a possible approach to minimize the volume of secondary radioactive waste, and cumulative pre-concentration factors were recorded for both cations.

Partitioning and speciation of Pu in the sedimentary rocks aquifer from the deep liquid nuclear waste disposal

Abstract Plutonium partitioning and speciation was studied under the conditions of a liquid nuclear waste repository site. The dominating effect of corrosion products (Fe and Cr) oxides on plutonium partitioning was established in batch sorption tests at 150 ℃ and by using sequential extraction. Various techniques including Mössbauer spectrometry, XRD and TEM were used to characterize Fe/Cr oxide phases that form both precipitates and surface coatings which sorb plutonium. The sorption and speciation of plutonium was modeled thermodynamically using Pourbaix diagram that takes into account both surface complexation reaction and precipitation of insoluble PuO2.

Sorption and Speciation of Uranium on Silica Colloids

Sorption behavior of uranium onto silica colloids is studied to derive surface complexation data. Several spectroscopic and structural methods, i.e., Time-resolved Laser-induced Fluorescence (TRLIF), X-ray Absorption Fine Structure (XAFS), and Small-angle X-ray Scattering (SAXS) are employed for characterization of colloid suspensions and surface-sorbed species. TRLIF and EXAFS allowed identification of two principal uranium species on the silica surface – bidentate coordinated uranyl complexes of the following stoichiometries (≡SiO)2UO2 and (≡SiO)2UO2OH−. No polynuclear species or surface precipitates are formed as shown by EXAFS and SAXS examination of suspensions at various silica/uranium ratios. However, when uranium coverage of the silica surface exceeds 7%, the colloid stability as determined by electrophoretic mobility increases. Potentially, this could affect colloid-facilitated transport.

Sorption of actinides onto nanodiamonds

Abstract Detonation nanodiamonds (ND) present a significant part of nanocarbons group, which could be produced on commercial scale by detonation of explosives in a closed chamber. Their unique properties of high surface area, low weight and radiation resistance make ND a prospective candidate for applications in sorption processes in radiochemistry. To study the influence of surface chemistry on sorption properties, apristine sample of ND was treated with acids and hydrogen. The surface chemistry of the samples was characterised by infrared spectroscopy, X-ray photoelectron spectroscopy and Boehm titration. The sorption properties of ND were tested fordifferent radionuclides. The sorption capacity of ND was shown to be higher than those of commonly used radionuclide sorbents like activated carbon and compariable to other members of nanocarbon group like graphene oxide and carbon nanotubes. The sorption properties were shown to be influenced by the presence of oxygen-containing groups on the surface of ND. This represents an opportunity to increase the sorption capacity of ND.

The role of colloid particles in the albumin-lanthanides interaction: The study of aggregation mechanisms

We studied the interaction between bovine serum albumin (BSA) and lanthanide ions in aqueous solution in the 4.0÷9.5pH range. A strong increase of the solution turbidity was observed at pH values exceeding 6, which corresponds to the formation of Ln(OH)3 nanoparticles, while no changes were observed near the isoelectric point of BSA (pH 4.7). The results of the dynamic light scattering and protein adsorption measurements clearly demonstrated that the observed turbidity enhancement was caused by albumin sorption on the surface of Ln(OH)3 and colloid particles bridging via adsorbed protein molecules. Upon pH increase from 4.5 to 6.5, albumin adsorption on lanthanide colloids was observed, while the following increase of pH from 6.5 to 9.5 led to protein desorption. The predominant role of the electrostatic interactions in the adsorption and desorption processes were revealed in the zeta-potential measurements. No reversibility was observed upon decreasing pH from 9.5 to 4.5 that was suggested to be due to the other interaction mechanisms present in the system. It was shown that while for all lanthanide ions the interaction mechanism with BSA was similar, its manifestation in the optical properties of the system was significantly different. This was interpreted as a consequence of the differences in lanthanides hydrolysis constants.

Rapid method for the purification of graphene oxide

A rapid and facile purification method for graphene oxide (GO) is important for its production above the gram scale. Such a method would allow for the development of GOs large-scale industrial applications. Out of several protocols in this study, including centrifugation, filtration, precipitation and decantation, filtration using a gas-press proved to be the most effective. Gas-press filtration using filter beds of Celite, perlite, glass wool, ceramic tape, or woven glass fibre allowed for adequate purification of 1 g of crude large-flake (∼30 μm flake diameter) GO in less than 60 min using a lab-scale set-up. The present technique could be easily scaled-up, it generates minimal waste, and can be tuned by changing the dimensions of the equipment, pressure, and filter bed. This would allow a user to obtain a higher work-up efficiency. The quickly purified product is called efficiently purified GO or EGO.

Photoreduction of Pu(V,VI) by TiO2

Abstract In this study, the effect of light on the kinetics and speciation of plutonium at its interaction with particles of TiO2 under different light conditions is shown for the first time. It was found that sorption was followed by reduction of the plutonium to Pu(IV). In this, the reduction reaction and sorption in conditions of the presence of light proceed significantly more rapidly due to the photocatalytic activity of titanium dioxide, providing a source of electrons for the reaction. Spectral methods (XAFS and TEM) showed that plutonium forms nanoclusters with the structure of PuO2, which decorate the surface of the solid phase.