Investigations on the interactions of organo-clay minerals with radioiodine

The relation between the mineralogical properties of clay minerals treated with quaternary alkylammonium ions and their sorption characteristics for radioiodine was studied using the batch method. The increased distribution ratios (Rd-values) for 125I- found in vermiculite treated with different alkylammonium ions were accompanied by increased organic C-contents and the expansion of the basal spacings of the organo clays. Measurements confirmed that substances with long C-chains were effective in producing organo-clays with high iodine sorbing capacity, whereas ammonium salts without side chains showed neither intercalation into the silicate layers nor increased iodine sorption. In addition to the type of the organic cations, the applied concentrations of the alkylammonium ions influenced their uptake and the iodine fixing efficiency of the organo-clay complex. Maximum uptake and iodine sorption was obtained at about 50% exchange of the interlayer cations. Tests with 134Cs+ revealed that the partial modification makes the organo-clays also capable for the sorption of inorganic cations. X-ray diffractograms showed both interstratified layer structures (HDPY+ and Mg2+ saturated layers) and beside it unaltered vermiculite in clay minerals with partially exchanged metal cations. Furthermore, the size-dependence of the silicate particles was investigated: The highest alkylammonium ion incorporation and iodide sorption was found in the clay fraction of 0.6-2 μm. (orig.)