Tachi Y, Shibutani T, Sato H, Yui M
Japan Nuclear Cycle Development Institute (JNC), Tokai Works, 4-33 Muramatsu, Tokai, Ibaraki 319-1194, Japan.
J Contam Hydrol. 2001 Feb;47(2-4):171-86. doi: 10.1016/s0169-7722(00)00147-9.
The sorption and desorption behavior of radium on bentonite and purified smectite was investigated as a function of pH, ionic strength and liquid to solid ratio by batch experiments. The distribution coefficients (Kd) were in the range of 10(2) to > 10(4) ml g-1 and depended on ionic strength and pH. Most of sorbed Ra was desorbed by 1 M KCl. The results for purified smectite indicated that Ra sorption is dominated by ion exchange at layer sites of smectite, and surface complexation at edge sites may increase Ra sorption at higher pH region. Reaction parameters between Ra and smectite were determined based on an interaction model between smectite and groundwater. The reaction parameters were then used to explain the results of bentonite by considering dissolution and precipitation of minerals and soluble impurities. The dependencies of experimental Kd values on pH, ionic strength and liquid to solid ratio were qualitatively explained by the model. The modeling result for bentonite indicated that sorption of Ra on bentonite is dominated by ion exchange with smectite. The observed pH dependency was caused by changes of Ca concentration arising from dissolution and precipitation of calcite. Diffusion behavior of Ra in bentonite was also investigated as a function of dry density and ionic strength. The apparent diffusion coefficients (Da) obtained in compacted bentonite were in the range of 1.1 x 10(-11) to 2.2 x 10(-12) m2 s-1 and decreased with increasing in dry density and ionic strength. The Kd values obtained by measured effective diffusion coefficient (De) and modeled De were consistent with those by the sorption model in a deviation within one order of magnitude.
通过批量实验研究了镭在膨润土和提纯蒙脱石上的吸附和解吸行为，该行为是pH值、离子强度和液固比的函数。分配系数（Kd）在10²至>10⁴ml g⁻¹范围内，且取决于离子强度和pH值。大部分吸附的镭被1M KCl解吸。提纯蒙脱石的结果表明，镭的吸附主要由蒙脱石层间位点的离子交换主导，边缘位点的表面络合作用可能会在较高pH区域增加镭的吸附。基于蒙脱石与地下水之间的相互作用模型确定了镭与蒙脱石之间的反应参数。然后通过考虑矿物和可溶性杂质的溶解和沉淀，用这些反应参数来解释膨润土的实验结果。该模型定性地解释了实验Kd值对pH值、离子强度和液固比的依赖性。膨润土的模拟结果表明，镭在膨润土上的吸附主要由与蒙脱石的离子交换主导。观察到的pH依赖性是由方解石溶解和沉淀引起的钙浓度变化导致的。还研究了镭在膨润土中的扩散行为与干密度和离子强度的关系。在压实膨润土中获得的表观扩散系数（Da）在1.1×10⁻¹¹至2.2×10⁻¹²m² s⁻¹范围内，并随干密度和离子强度的增加而降低。通过测量有效扩散系数（De）和模拟De获得的Kd值与吸附模型得到的Kd值在一个数量级偏差内一致。
