Sci Total Environ
Department of Earth and Environmental Sciences, Division of Soil and Water Management, KU Leuven, Kasteelpark Arenberg 20, 3001 Leuven, Belgium.
Published: June 2020
The Neogene-Paleogene glauconite sands of Belgium cover the Boom Clay deposits that are candidate host for radioactive waste disposal. It is unclear if the highly permeable sand formations may act as an additional barrier for radiocesium (Cs) or could be added as a complementary sorption sink in a surface disposal concept. Glauconite is an Fe-rich phyllosilicate that is mainly present as 250-125 μm sized pellets in sand, it is unknown to what extent and how fast these pellets may bind Cs. Pelletized clays embedded in sand may have poorly accessible high affinity sites for Cs. The Cs sorption on 11 different glauconite sands was measured in batch in a background solution of 0.1 M CaCl and 0.5 mM KCl. The log transformed Cs distribution coefficient K (L kg) after 30 days reaction ranged 3.4-4.3, surprisingly close to the K of the Boom Clay (3.5). Isolated glauconite fractions exhibited similar Cs sorption potentials (log K 4.1-4.3) as the reference Illite du Puy (4.4). The small K variation among the Neogene-Paleogene sands was explained by its glauconite content (r = 0.82). The Cs sorption kinetics (1-57 days) of milled pellets (<2 μm) confirmed slower reaction with intact pellets than with milled samples. Additionally, the K values of milled samples (57 days) sorption are 1.1-1.5 fold larger than the corresponding intact pellets, suggesting that not all Cs binding sites are accessible in intact pellets. Strongly weathered pellets exhibited cracks (visible with SEM). In these pellets the K was similar for milled and intact pellets suggesting that cracks increase the accessibility of the inner sorption sites. After 8.5 months the K values were 1.6-1.8-fold above corresponding 1 month data and these long-term reactions were more pronounced as total sand K content was larger. An adsorption-desorption experiment illustrated that Cs sorption is not fully reversible.
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http://dx.doi.org/10.1016/j.scitotenv.2020.137392 | DOI Listing |
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