A Batch Experiment of Cesium Uptake Using Illitic Clays with Different Degrees of Crystallinity

Abstract

Radiocesium released by the severe nuclear accident and nuclear weapon test is a hazardous material. Illitic clays play a key role in the spatial distribution of radiocesium in groundwater environments due to selective uptake sites at the illite mineral, such as frayed edge sites. However, the cesium uptake capabilities of illitic clays are diverse, which could be associated with the illite crystallinity. This study was performed to determine the cesium uptake of illitic clays and evaluate the crystallinity effects on cesium uptake using statistical approaches. A total of 10 illitic clays showed various crystallinity, which was parameterized by the full width at half maximum (FWHM) at 10 Å XRD peak ranging from 0.15 to 0.64. The uptake behavior of illitic clays was well fitted with the Freundlich model (i.e., r2 > 0.946). The uptake efficiency of illitic clays increased with the decrease in dissolved cesium concentrations. The cesium uptake was significantly correlated with the FWHM and cation exchange capacity, suggesting that the uptake becomes higher with decreasing crystallinity through expansion of the edge site and/or formation of ion-exchangeable sites.

Emerging investigator series: a holistic approach to multicomponent EXAFS: Sr and Cs complexation in clayey soils

“…The values for Sr and Cs adsorption with the mineral phases and the composite clayey soil samples correspond well with % adsorbed and distribution coefficients (K D values) determined in recent research on Sr and Cs complexation with clay minerals, metal oxides and clayey soils. 1,15,16,18,19,23,27,29,30,39,[57][58][59][60][61][62][63] The similarities with previous results on Sr complexation with clay minerals, metal oxides and clayey soils indicate that any stable Sr present in the mineralogical samples did not significantly affect Sr surface complexation at 20 Bq/ml Sr-85 to the single mineral phases or the composite clayey soil. Adsorption of Cs and Sr to anatase.…”

“…S1), 24,25,31,37,38 and/or complexation at their frayed edges sites. 29,30,39 In contrast to the adsorption of Cs to the LFLS core samples, Sr adsorption to most of the LFLS core samples was higher compared to its adsorption to the composite clayey soils (Fig. 2a) with the exception of the LFLS core sample 'CH30 1.0-1.2 m' where adsorption was similar to that for the composite clayey soils (Fig.…”

“…These differences (in absolute values, and in the trend as a function of pH) suggest differences in the mechanisms of Cs interaction with illite-smectite at trace and at elevated concentrations. These different mechanisms depend on concentration and surface coverage and can include diffusion into the interlayer of illite-smectite 24,25,31,37,38 and complexation at the frayed edges sites 29,30,39 at trace concentrations, and outer sphere surface complexes, 24,[32][33][34] and complexation at the silicon vacancies on the basal surfaces 19,35 at elevated concentrations. Sr complexation with illite-smectite was significant, and show similar trends with varying pH values, at both trace and elevated Sr concentrations.…”

“…suggesting that at trace concentrations, Cs complexation and mobility is governed by its interaction with illite-smectite, likely through its diffusion and incorporation into their interlayers 25,31,37,38 and/or complexation at the frayed edges sites. 29,30,39 Adsorption of Cs and Sr to Little Forest Legacy Site (LFLS) core samples. The results from the complementary Cs and Sr adsorption experiments to the LFLS core samples are summarized in Table S8 and visualized in Fig.…”

“…19 Conversely, at trace concentrations Cs has been shown to incorporate into the interlayers of 2:1 clay minerals, 24,25,31,37,38 and complexes to the frayed edge sites, 29,30,39 dependent on the crystallinity of such clay minerals. 39 The above described complexation with mineral phases can inhibit the uptake of metals and contaminants by fungi and vegetation, impacting on their toxicity, [40][41][42][43] and/or retain metals within their environment. 43 Any engineering strategy designed to limit the environmental impacts of such fission products will impact on their surface speciation and consequentially on their mobility and toxicity within the environment.…”