Retardation capacity of organophilic bentonite for anionic fission products

Sorption and diffusivity of iodide and pertechnetate (I- and TcO4-) on MX-8 0 bentonite with different hexadecylpyridinium (HDPy+) loadings were studie d using equilibrium solutions of different ionic strengths. In HDPy+-modifi ed bentonite, iodide and pertechnetate ions exhibited increasing sorption ( characterized by the distribution ratio, R-d), while Cs+ and Sr2+ showed de creasing sorption with increasing organophilicity. In case of medium-loadin g levels, the simultaneous sorption of anions (I- and TcO4-) and cations (C s+ and Sr2+) was observed. Sorption of ions was influenced by the composition of the electrolytes empl oyed. It decreased gradually with increasing ionic strength of the electrol yte solutions. The experiments revealed the general tendency that the diffusivity (D-a [cm (2).s(-1)]) for iodide and pertechnetate decreases with increasing organoph ilicity and increases with increasing ionic strength of the equilibrium sol utions, confirming the results of the sorption experiments. Additionally, some mineralogical and chemical investigations, like IR spect ral analysis of the organo-bentonite samples and exchange behavior of HDPy, were performed. On the basis of these analyses, it was concluded that the alkylammonium ions are sorbed as (1) HDPy+ cations, (2) HDPyCl molecules a nd (3) micelles with decreasing binding intensities in this order. (C) 2001 Elsevier Science B.V. All rights reserved.