Freundlich and dual Langmuir isotherm models for predicting 137Cs binding on Savannah River Site soils.
Distribution of 137Cs and stable cesium between aqueous solution and near-surface soil samples from five locations at the Savannah River Site was measured in order to develop a predictive model for 137Cs uptake by the soils. Sorption of 137Cs in these soils appears to be mostly by hydroxy-interlayered vermiculite. Batch sorption studies with 4 d for equilibration were conducted at three cesium concentrations and at two backing electrolyte (NaNO3) concentrations. The soil-solution mixtures were pH-adjusted to evaluate the effects of pH on cesium sorption. Sorbed cesium was related to the equilibrium aqueous cesium concentrations by a Freundlich isotherm model. Model fits on logarithmic scales have a common slope of 0.60 +/- 0.03 for acidic mixtures and 0.69 +/- 0.04 for neutralized mixtures but have unique intercepts that are influenced by backing electrolyte concentration and pH. An ion-exchange model is proposed that pertains to all five soils and relates the Freundlich isotherms to the cation exchange capacity of soil and the aqueous concentrations of cesium, sodium, and a third ionic species that was hydrogen in the acidic mixtures and potassium in the neutralized mixtures. Model fits are consistent with Kd values in the entire range of 5-2,300 L kg(-1) determined for the five soil types. As an alternate model, dual Langmuir isotherms were fitted to the data. The results suggest cesium sorption by (1) relatively few interlayer-wedge sites, highly selective for cesium, and (2) much more abundant but less selective sites on internal and external planar surfaces.
Goto
Momoko
M
Nuclear and Radiological Engineering Program, Woodruff School of Mechanical Engineering, Georgia Institute of Technology, Atlanta, GA 30332, USA.
Rosson
Robert
R
Wampler
J Marion
JM
Elliott
W Crawford
WC
Serkiz
Steven
S
Kahn
Bernd
B
D000327:Adsorption; D002586:Cesium / Q000032:analysis* / Q000737:chemistry; D006863:Hydrogen-Ion Concentration; D008962:Models, Theoretical; D045483:Rivers; D012990:Soil Pollutants, Radioactive / Q000032:analysis* / Q000737:chemistry
D012990:Soil Pollutants, Radioactive; D002586:Cesium