Size distribution of alkali elements in riverbed sediment and its relevance to fractionation of alkali elements during chemical weathering

Mineralogical control of the size distribution of stable Cs and radiocesium in riverbed sediments

“…The fact that these minerals were contained in the sediments is consistent with the geology of the Abukuma River system (Kamei et al, 2003). All the identified minerals were also found in the sediments from the pasture site (Tanaka and Watanabe, 2015). Moreover, the difference in mineralogical composition between the Kuroiwa and pasture sites is noteworthy.…”

“…1, 137 Cs concentrations in the sizefractioned sediments were already measured in . Additionally, the chemical compositions and the mineralogy of the sediments from the pasture site were reported in Fan et al (2014a) and Tanaka and Watanabe (2015). In the following sections, we describe the analytical procedures only for the new data obtained in this study.…”

“…Sand fractions (>63 mm) were crushed and pulverized into fine powders with an agate mortar to facilitate the subsequent sample decomposition. Forty milligrams of each sample were decomposed with 2 ml 38%-HF and 1 ml 70%-HClO 4 in a sealed Teflon vessel at 160∞C on a hot plate (Tanaka and Watanabe, 2015). After evaporation to dryness, the same treatment was repeated to the residue with half the volume of the HF and HClO 4 .…”

“…However, it is often difficult to distinguish the influence of particle size and mineralogical composition on the size distribution of radiocesium because they are closely related. Clay minerals are concentrated in fine grain fractions primarily by chemical weathering of granitic rocks (Nesbitt et al, 1996Tanaka and Watanabe, 2015). Weathering of other rocks, such as sedimentary rocks and volcanic rocks, can also produce fine clay minerals.…”

“…Once radiocesium dissolves in meteoritic water, it must follow the behavior of stable Cs ( 133 Cs), which is originally distributed on earth, in its interaction at the solid-water interface. Therefore, the distribution of 133 Cs is important for understanding the behavior of radiocesium in the environment (Wampler et al, 2012;Fan et al, 2014a;Saito et al, 2014;Tanaka and Watanabe, 2015). Moreover, bulk chemical compositions of sediments are determined by their mineralogical compositions.…”