Affinity of radioactive cesium and strontium for illite and smectite clay in the presence of groundwater ions

Abstract

Sorption behaviour of hazardous nuclides such as 137 Cs and 90 Sr onto illite and smectite clay was studied in the presence of major groundwater ions (Ca 2+ , Mg 2+ , K + , Na + and HCO 3 -). Illite and smectite clay can selectively sorb small hydrated Cs + ion in the presence of groundwater cations except K + ion. In contrast, sorption of larger and stable hydrated Sr 2+ ion onto illite and smectite clay is highly competed by background groundwater cations. The sorption characteristics of Cs + and Sr 2+ onto illite and smectite clay are 2173 JEONG ET AL. closely related to hydration properties of ions and complex forms of ions (inner-sphere or outer-sphere complex) in the siloxane cavity of clay minerals. The mechanism of Cs + and Sr 2+ sorption of illite is ion exchange with an interlayer cation K + , and K + , Ca 2+ and Mg 2+ , respectively. The effect of bicarbonate ion on Sr 2+ sorption of illite is due to the change of pH and the precipitation of a solid phase (SrCO 3 ). The zeta potentials of illite and smectite clay as a function of pH reflect surface charge characteristics of two clay minerals. The results of this study indicate that the transport of 137 Cs in geologic barrier of a radioactive waste repository would be greatly retained by illite and smectite clay, and that the fate of Sr would be significantly controlled by ionic strength of groundwater cations and bicarbonate ion as a complex agent.

Clay mineral weathering and contaminant dynamics in a caustic aqueous system

“…13a-c). This result is consistent with high illite selectivity for Cs relative to Sr (Jeong et al, 1996;Dyer et al, 2000;Zachara et al, 2002) and the limited density of accessible charged sites in illite (Ͻ 150 mmol c kg Ϫ1 ) for sorption of the hydrated Sr ion. Both Sr and Cs showed near complete sorption to vermiculite platelets after 1 y reaction time as indicated by wet chemistry data (Fig.…”

The uptake of radioisotopes onto clays and other natural materials

“…1 Additional comments have already highlighted the influence of the H + cation, the lack of anion control (except in cases of ruthenium species uptake), and the small effects seen when iron and magnesium cations are present, The results were is general agreement with those of JEONG et al 6 They examined Cs and Sr removal from ground waters by illite and smectite. The presence of potassium was alone in reducing Cs uptake amongst, but Sr uptake was greatly affected by backgrotmd water cations.…”

Silicon control of strontium and cesium partitioning in hydroxide-weathered sediments

“…sorbents at low Cs + sorbate concentrations (Jeong et al, 1996;Wauters et al, 1996;Sutton and Sposito, 2002) is applicable even under the extremely high ionic strength and pH conditions imposed. The non-labile (residual) pool of sorbed Cs + also increases in the order HC > HF > RS (see top three graphs in Fig.…”

“…This facilitates its inner-sphere coordination at charged siloxane sites on layer silicate surfaces and results in a particularly high affinity for frayed edge sites of micaceous minerals (Cornell, 1993;Kim et al, 1996;Sutton and Sposito, 2001;Bostick et al, 2002;Steefel et al, 2003). Similar in ionic potential to Ca 2+ , the Sr 2+ cation has higher hydration energy than Cs + and it typically forms outer-sphere surface complexes at negatively charged sites on clay minerals and oxides (Jeong et al, 1996;Sahai et al, 2000). Strontium mobility is also influenced by co-precipitation in CaCO 3 (s) or discrete SrCO 3 (s) precipitates (Parkman et al, 1998;Sahai et al, 2000;McKinley et al, 2007).…”