Radiocesium reaction with illite and organic matter in marine sediment

Abstract

The mineralogical effect on the 137Cs reaction with marine sediment has not been systematically studied yet, even though illite has been known to adsorb Cs preferentially on its frayed edge sites in a low Cs concentration. Ninety-three marine sediment samples were collected near Yangnam, Korea for quantitative X-ray-diffraction (XRD), gamma-ray, and total organic carbon (TOC) analysis. Illite content was in the range of 0–23 wt.% and those of 137Cs and TOC were minimum detectable activity (MDA) ∼ 7.19 Bq/kg-dry and ∼3.32%, respectively. The illite content in the marine sediment showed a good relationship with the 137Cs content ( R 2 = 0.69), but with an increase in the illite content, the relationship became less linear. This trend can be clearly shown in two groups of samples with different size fractions (< and >5Md ϕ). For the samples of larger particle sizes (low contents of illite), the relationship is linear, but for the samples of the smaller particle sizes (high illite content) it is less linear with a decreased slope, indicating that increase in illite content does not significantly contribute to the fixation of 137Cs in marine sediment. Rather, the TOC has a more linear relationship with 137Cs content with no slope change in all particle size ranges. This may indicate that humic materials in marine sediment block the access of 137Cs to the frayed edge site and reduces the adsorption of 137Cs on illite and that the organic materials in marine sediment play more important roles in adsorbing Cs than illite.