Spatially resolved sorption of Cm(III) on crystalline rock: influence of surface roughness and mineralogy

Many countries will use deep geological repositories to dispose of highly active nuclear waste. Crystalline rock is a potential host rock because of its strong geotechnical stability, low permeability and low solubility; however, its inherent mineralogy is heterogeneous, consisting of a wide set of minerals in varying amounts. Therefore, there is a need for using sophisticated techniques that allow spatial resolution to characterize the nanostructure of such crystalline rock surfaces and the speciation of the actinides therein. As a representative for trivalent actinides, such as Am(III), Np(III), and Pu(III), which are expected to be present due to the reducing conditions encountered in a deep geological repository, we have chosen the actinide Cm(III). Cm(III) possesses excellent luminescence properties, which allows us to not only examine the sorption uptake but also the speciation of Cm(III) on the surface. We combined spatially resolved investigation techniques, such as vertical scanning interferometry, calibrated autoradiography, and Raman microscopy coupled to micro-focus time-resolved laser-induced luminescence spectroscopy (µTRLFS) (Molodtsov et al., 2019). Thus, we were able to correlate mineralogy, surface roughness, and grain boundary effects with radionuclide speciation, allowing us to identify important radionuclide retention processes and parameters (see Fig. 1). Investigations focused on granite from Eibenstock (Germany) and migmatised gneiss from Bukov (Czech Republic). Cm(III) sorption on the rock's constituting minerals – primarily feldspar, mica and quartz – was analyzed quantitatively and qualitatively. We observed that Cm(III) sorption uptake and speciation depends not only on the mineral phase but also the surface roughness (Demnitz et al., 2021). An increasing surface roughness leads to higher sorption uptake and a stronger coordination of the sorbed Cm(III). On the same mineral grains sorption differed significantly depending if an area exhibits a low or high surface roughness. In the case that one mineral phase dominates the sorption process, sorption of Cm(III) on other mineral phases will only occur at strong binding sites, typically where surface roughness is high. Areas of feldspar and quartz with high surface roughness additionally showed the formation of sorption species with particularly high sorption strength that could either be interpreted as Cm(III) incorporation species or ternary complexes on the mineral surface (Demnitz et al., 2021). We conclude that in addition to mineral composition, surface roughness needs to be adequately considered to describe interfacial speciation of contaminants and respective retention patterns for the safety assessments of nuclear waste repositories.

The synthesis of bayberry-like mesoporous TiO2 microspheres by a kinetics-controlled method and their hydrophilic films

Bayberry-like mesoporous TiO2 hydrophilic films with high surface roughness and high density of surface hydroxyl groups.

Influence of chemical postprocessing on mechanical properties of laser-sintered polyamide 12 parts

A limiting factor for industrial usage of laser-sintered parts is the high surface roughness due to the semi-molten or attaching powder particles resulting from tool and pressureless manufacturing. An approach to improve the surface quality is the postprocessing with acids to smoothen the surface as it enables improvement without geometrical restrictions of the parts. The present work deals with the usage of nitric, hydrochloric, and trifluoroacetic acids, and exhibits the influence on the resulting surface morphology, dimensional accuracy, and the mechanical properties. The results exhibit different interaction mechanics and show great differences in the resulting part properties.