Nonequilibrium Sorptive Behavior of Cobalt, Cesium, and Strontium on Bandelier Tuff: Experiments and Analysis

摘要

Information is presented on the nonequilibrium sorption of cobalt, cesium and strontium on Bandelier Tuff. Both adsorption and desorption were studied in the batch at 25 degrees C with constant mixing. The reaction solutions consisted of 20 mg/L of stable cobalt, cesium or strontium with their radioactive tracers sup 60 Co, sup 137 Cs or sup 85 Sr, in 0.01N CaCl sub 2 solution. Adsorption equilibrium occurs rapidly for strontium, somewhat more slowly for cesium, and very slowly for cobalt. The degree of adsorption is approximately 19% for stronium 49% for cesium, and 84% for cobalt. Desorption (leaching) initially occurs in a relatively rapid step followed by a much slower rate. The relative adsorption and desorption rates can be explained or predicted by theoretical considerations of the Modified Freundlich isotherm and Hill Plot analyses of equilibrium sorption data. The Modified Freundlich isotherm analysis predicts that soil will exhibit ranges in relative energies of sorption and in reaction rates; the Hill Plot analysis predicts interactions among sorption sites. Nonequilibrium sorption data indicate that the ranges in relative energies and reaction rates are different for specific solutes and are dependent on interactions among sorption sites; the greater the interaction among sorption sites, the greater the range of reaction rates. The results of this study suggest that equilibrium models may be adequate to describe the movement of strontium in Bandelier Tuff under dynamic flow conditions. However, nonequilibrium models, in all probability, will be needed to describe the movement of cesium and cobalt under those same conditions. 9 references, 6 figures, 4 tables. (ERA citation 10:019273)