Radiocesium reaction with illite and organic matter in marine sediment.

Department of Geology, Kyungpook National University, Daegu 702-701, Republic of Korea.
Marine Pollution Bulletin (Impact Factor: 2.53). 06/2006; 52(6):659-65. DOI: 10.1016/j.marpolbul.2005.10.017
Source: PubMed

ABSTRACT The mineralogical effect on the (137)Cs 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 (137)Cs and TOC were minimum detectable activity (MDA) approximately 7.19 Bq/kg-dry and approximately 3.32%, respectively. The illite content in the marine sediment showed a good relationship with the (137)Cs 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 >5Mdvarphi). 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 (137)Cs in marine sediment. Rather, the TOC has a more linear relationship with (137)Cs content with no slope change in all particle size ranges. This may indicate that humic materials in marine sediment block the access of (137)Cs to the frayed edge site and reduces the adsorption of (137)Cs on illite and that the organic materials in marine sediment play more important roles in adsorbing Cs than illite.

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    ABSTRACT: The controlling factors affecting the accumulation of (137)Cs in marine sediment have not been investigated in detail, especially in coarse grained sediment. Eighty eight coarse marine sediment samples near Wuljin, Korea, were characterized by quantitative X-ray-diffraction (XRD), gamma-ray, and total organic carbon (TOC) analysis. Those factors were then compared. The grain size was in the range of -0.48 to 3.6Mdphi corresponding to sand grains. TOC content was in the range of 0.06-1.75%, and the concentration of (137)Cs was <MDA to 4.0Bq/kg-dry. The main identified minerals were general rock-forming minerals such as quartz, feldspars with minor contents of pyroxene, calcite, hornblende, a 10A phase of phyllosilicate assigned to biotite, and chlorite. Other clay minerals were not identified due to the large grain sizes of the investigated samples. Biotite (1-7wt%) was the only mineral showing a positive correlation with (137)Cs activity, which was first reported here, probably due to the weathered frayed edge site of biotite produced by a release of K. The samples with low TOC contents showed even better correlation between biotite content and (137)Cs activity. For the entire samples, however, the TOC content showed better correlation with (137)Cs activity than other single factors, indicating that biotite and organic carbon are the most important factors controlling (137)Cs fixation. The combined effect of biotite and TOC for (137)Cs fixation was also confirmed by multiple regression analysis ((137)Cs activity=1.712.TOC (wt%)+0.202.biotite (wt%)-0.097; R(2)=0.819). The regressed slopes indicated that the (137)Cs-adsorption capacity of TOC was about 8.5 times higher than that of biotite. However, the amount of (137)Cs adsorbed onto biotite was 30% more than that adsorbed onto TOC due to much greater biotite content in the sediment. The role of biotite in fixing (137)Cs becomes more important in sediment with coarser grains, containing little TOC.
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  • CIESM; 01/2010
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    ABSTRACT: The relationship between cesium (Cs) adsorption on clay minerals with various expandabilities and Cs mobility in environment was investigated using sequential extraction, batch adsorption, X-ray diffraction (XRD), generalized adsorption model (GAM), and Cs LIII-edge extended X-ray absorption fine structure (EXAFS) analyses with molecular simulations using the density functional theory (DFT). In particular, the difference between the affinities of illite (non-expansion) and vermiculite (intermediate expansion) for Cs and the effect of humic acid (HA) addition on the Cs/clay mineral system were highlighted in this study. These two factors affect Cs mobility and bioavailability in surface soil and sediments. The batch adsorption results showed that Cs adsorption was inhibited to some extent in the ternary clay + HA + Cs system because of (i) the blocked access of Cs to the frayed edge site (FES) and type II site [inner–sphere (IS) complex in GAM] by HA, and (ii) the reduced availability of the interlayer site in vermiculite. EXAFS analysis further confirmed that the adsorbed Cs in clay minerals was drastically changed by the sequential addition of HA. In addition, the dominant IS complex in the illite + Cs and illite + Cs + HA systems (in which HA was added after Cs adsorption on illite) can be converted to the outer–sphere (OS) complex largely in the illite + HA + Cs system (in which HA was added prior to Cs adsorption). These results are consistent with the sequential extraction and GAM results. The IS complex of dehydrated Cs+ mainly formed at the FES and interlayer site on illite (non-expansion) without resulting in any illite structural changes. However, on vermiculite (intermediate expansion), the dehydrated Cs+ can be adsorbed as an IS complex associated with the siloxane group of the di-trigonal cavity in the tetrahedral SiO4 sheet. This adsorption is accompanied by collapse of the layer, which can be easily coated by HA molecules to prevent Cs fixation. However, a nearly complete OS complex was observed at the planar site of montmorillonite (large expansion). These processes were confirmed by sequential extraction, batch adsorption, XRD, and EXAFS, which clearly showed that Cs mobility in soil highly depends on clay mineral expandability, natural organic matter (NOM), and the coupling of both effects. The atomic-scale information given by EXAFS is consistent with the distribution data from adsorption experiments, GAM, sequential extraction, and DFT. These results can be used as a basis for a clearer understanding of Cs behavior in natural systems.
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