Experimental and modeling studies of caesium sorption on illite
A natural illite (illite du Puy) was purified and converted to the homo-ionic Na form. The conditioned Na-illite was characterized in terms of its mineralogy, chemical inventory, and surface properties. The structural formula was determined from EDS analyses (SEM/TEM) and bulk chemistry. A cation exchange capacity of 127 mEq/kg was determined by the Na isotope dilution method at neutral pH. The sorption of Cs was measured as a function of NaClO{sub 4} background electrolyte concentration (1.0, 0.1 and 0.01 M), Cs concentration and pH in the range {approx}3 to {approx}10. Before obtaining these measurements the kinetics of Cs uptake were determined at initial concentrations of 2 x 10{sup {minus}8} M and 7 x 10{sup {minus}5} M, representing the extremes of the range investigated, and was found to be concentration dependent. The supernatant solutions after centrifugation were analyzed for major cations in all of the sorption tests. A two-site cation exchange model was developed to describe the sorption of Cs over the whole range of experimental conditions. The two-site types were termed frayed edge sites, FES (high affinity/low capacity) and type 2 sites (low affinity/high capacity). At low NaClO{sub 4} concentrations, Cs sorption decreased at pH values less than neutral. This was interpreted in terms of competitive effects from H, and K released by the partial dissolution of illite, which cannot be avoided at low and high pH values. Selectivity coefficient values for Cs-Na, Cs-K, K-Na, and H-Na exchange equilibria on the FES sites, and Cs-Na exchange on the type 2 sites are given for illite together with the corresponding site capacities.
- Research Organization:
- Paul Scherrer Inst., Villigen PSI (CH)
- OSTI ID:
- 20003974
- Journal Information:
- Geochimica et Cosmochimica Acta, Vol. 63, Issue 19-20; Other Information: PBD: Oct 1999; ISSN 0016-7037
- Country of Publication:
- United States
- Language:
- English
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