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.
Highlights
The Fukushima nuclear accident that occurred on 11 March 2011 resulted in widespread radionuclide contamination over the Northern Hemisphere
A total of 10 illitic clays (YC1 to YC8, Chuzhou illite (CI), and Montana illite (MI)) were characterized to determine Brunauer– Emmett–Teller (BET), cation exchange capacity (CEC), illite contents, and crystallinity that are potentially associated with cesium uptake reactions (Table 1a)
The 10 Å X-ray diffraction (XRD) peaks (2θ ≈ 8.8◦), which indicated the d-spacing of a basal plane for illite, exhibited diverse kurtoses, suggesting the various crystallinity of illite in the illitic clays (Figure 1b)
Summary
The Fukushima nuclear accident that occurred on 11 March 2011 resulted in widespread radionuclide contamination over the Northern Hemisphere. The illitic clays play an important role in 137Cs uptake in the groundwater environment They have a relatively smaller cation exchange capacity than other expandable clay minerals [8,9,10,11,12], high selectivity sorption sites are present for 137Cs [12,13,14]. A few studies have developed cesium uptake models for illite, including cation exchange, surface complexation, and molecular simulations [12,13,16,21,22,23,24], and detected individual sorption sites using X-ray adsorption fine structure spectroscopy and transmission electron microscopy for complex uptake mechanism determination [17,19,25,26]. The illite crystallinity was applied as a relative indicator to predict the cesium uptake performance for the illitic clays
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