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In batch experiments with two types of soils, chernozem and podzol, radioiodine (125I) showed an initial rapid sorption, followed by a long and slow further increase. Very little sorption (Rd < 1) was detected in clay minerals. Generally, higher. Revalues were observed for the chernozem soil, characterized by a higher amount of organic substance and of soil biomass. The sorption process was predominantly irreversible, the isotherms were linear at low ion concentrations and deviated from linearity starting at 10-5 mmol - ml-1. Sorption ratio was found to increase with increasing volume to mass ratio. The composition of liquid phases (bidistilled water, synthetic soil water, rain water) highly affected iodine sorption. In experiments with KBr solution, the sorption of I “ was found to be strongly preferred to Br”. Incubation of soil samples under varied conditions (decreased or increased soil biomass, 02-concentration, incubation temperature, soil water content and storage conditions) delivered indications for the participation of soil microflora in iodine immobilization. Test with isolated soil bacteria and fungi showed that radioiodine can be incorporated by soil microorganisms under certain conditions only: Considerable uptake of radioiodine was found in washed (NaCl, CaCl2) cells with both bacteria and fungi, but no incorporation was detected into cells incubated with radioiodine in the culture medium. © 1991, Walter de Gruyter. All rights reserved

A B S T R A C T:Distribution coefficients and isotherms for the adsorption of radioiodide, caesium and strontium ions (125I-, 134Cs+ and 85Sr2+) were determined in untreated vermiculite and in vermiculite treated with the chloride salt of hexadecylpyridinium (HDPy+). Experimental data reveal that some of the alkylammonium ions were incorporated as HDPyCI ion pairs into the vermiculite. The fraction of ion pairs adsorbed is reflected by an increase in distribution coefficients with increasing saturation levels. Consequently, a considerable part of the iodide adsorption could be attributed to an anion exchange process. At smaller amounts of Cs § and Sr z+ adsorbed, distribution coefficients of the modified clay mineral are significantly reduced in comparison with the original material. These differences are less pronounced when greater amounts of cations are adsorbed. Generally, larger distribution coefficients were found for the Cs + compared with the Sr z § ion in the untreated and modified samples.

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Organo-clay / Radioiodine / Alkylammonium ions / Sorption / Migration / Rp-valuewith quaternary alkylammonium ions was investigated. AbstractIn the framework of investigations on the Sorption of radioiodine to natural and artificially altered soll components, a number of clay minerals and natural soils wäre treated with quaternary alkylammonium ions to replace the exchangeable metal cations. With help of batch experiments the resulting organo-clays were tested with respect to their sorption capability of radioiodine quantified by the distribution ratio (i?D-value).Treatment of bentonite, vermiculite and cretaceous clay as well as of samples from natural horizons of chernozem soil with hexadecylpyridinium (HDPY^) and benzethonium (BE^) exhibited sorption rates and amounts, which are several Orders of magnitude higher than those of the respective untreated samples. Moderate increases of the i?D-values were found after cation exchange with hexadecyltrimethylammonium (HDTMA^), while the applications of trimethylphenylammonium (TMPA"^) and tetramethylammonium (TM A ) were ineffecti ve. Considerable sorption of radioiodine was observed with the commercially available Bentone®.

A batch experiment with 1 "I revealed the general tendency of increasing distribution coefficients (^¿-values) with increasing organic C-content of different horizons of a podzolic soil profile. Column experiments with four pedologically distinct horizons confirmed this trend: An addition of compost in a concentration of 0.1 % to 1 % resulted in a marked increase of 1 "I sorption in a soil layer with organic C-deficiency. Precipitation and dialysis of the eluted organic substances suggest that a considerable part of the radioiodine is fixed in humic and fulvic acids.Addition of anthropogenic complexing agents such as dibutylphosphate (DBP), nitrilotriacetic acid (NTA) and ethylenediaminetetraacetic acid (EDTA) induced pronounced remobilization of iodine in the soil matrix.