Barrier materials and next-generation sorbents
An urgent problem of nuclear industry is the management of radioactive waste (RW) of variouscompositions, and ways to isolate them from the biosphere.
One of the industrial methods for treatment of aqueous solutions containing radionuclides is sorption that allows one to extract or separate the target components. The scientific task of this area of research is to develop scientific bases for the technology where different promising nanomaterials are applied for effective extraction of long-lived radionuclides (actinides and fission products) from aqueous solutions of various composition. Currently, we are performing the research with such nanomaterials as graphene oxide, various REE phosphates, titanium oxide, etc.
RW isolation requires the creation of a multi-barrier safety system according to the radiation safety requirements and international radioactive waste management regulations. The material of an engineering barrier must limit the inflow of ground water into the repository of radioactive waste, reduce the corrosion rate of RW-containing containers and matrices, and limit radionuclide migration into the environment. One of the most prospective components of engineering barriers are bentonite clays (bentonites), possessing high sorption and low water permeability properties, as well as various composite materials based on them. Sorption and diffusion properties of various barrier materials – clay minerals and host rock components – are being investigated as part of our work.
Main scientific results:
- Radionuclide interaction with graphene oxide has been studied in details. It was shown that during sorption on graphene oxide radionuclides are preferably interact with carboxyl groups located in defects of layers’ planes. Based on this result, graphene oxide with predominantly carboxyl surface groups has been synthesized, which led to an increase of radionuclide sorption by more than 15 times. To minimize the volume of subsequent radioactive waste repository, individual conditions to anneal graphene oxide samples after sorption of certain elements have been determined.
- It was demonstrated that increase of pH values in bentonite clay/ water systems promotes the sorption of Np(V) and Eu(III), and have almost no effect on the sorption of Cs(I). The increase in the ionic strength of the solution decreases the sorption of Cs(I) and Eu(III) and has almost no effect on the sorption of Np(V). It has been established that for Cs(I), the main chemical reaction occurring at the interface of bentonite clay/water phase is the ion exchange, complex formation with edge centers being the most characteristic for Np(V), with Eu(III) sorbed by both mechanisms. Thermodynamic modeling of the obtained experimental dependencies of radionuclide sorption has been performed. As a result, equilibrium constants of sorption reactions have been calculated.
- It has been determined that Cs(I) sorption varies depending on the individual characteristics of bentonite clays and considerably depends on the degree of heterovalent substitutions in smectite tetrahedral sublattice. It was found that the presence of goethite impurity in clays leads to a significant increase in Np(V) and Eu(III) sorption, but has no effect on cesium sorption. At the same time, the presence of competing cations in the solution significantly decreases the sorption of Cs(I).
- The contribution of each individual mineral to radionuclide sorption on the surface of granite has been determined and a semi-automated approach to the processing of radiographic data images developed.
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