Abstract In the geological disposal system of high-level radioactive and transuranic wastes, an increase in Ca concentration (arising from the alteration of cementitious materials) could affect the retention of other radionuclides due to competitive sorption. Batch sorption experiments were performed to investigate the sorption behavior of Ca and its competition with other divalent cations (Sr and Ni) on the edge sites of Kunipia F montmorillonite under alkaline conditions. Ca sorption increased with pH (when pH > 8) and it was more pronounced under high ionic strength conditions, indicating that Ca formed a surface complexation with the edge sites. The sorption behavior of Sr was similar to that of Ca. Meanwhile, the Ni sorption increased with pH, when this was >6 (for lower pH values than in the case of Ca and Sr), Ni tends to form surface complexes more readily than Ca and Sr. The results of a fitting analysis conducted based on the 2-site protolysis non-electrostatic surface complexation and cation exchange (2SPNE SC/CE) model indicate that Ca and Sr sorb onto the ≡SW2OH sites and Ni sorbs onto the ≡SSOH sites. Additionally, the sorption of the CaOH+ and SrOH+ ionic pair species by cation exchange was implied at pH ~ 12. Competitive sorption experiments were also carried out to evaluate the effect of Ca on the sorption of Sr and Ni. Sr sorption decreased with Ca concentration in the alkaline pH region, whereas Ni sorption was not affected by Ca concentration. Overall, these results indicate that Ca and Sr sorb onto the same sites, while Ca and Ni sorb onto different sites; additionally, the competitive sorption seemed to depend on chemical similarities (e.g., hydrolysis behavior). The sorption model parameters obtained from the single-element batch sorption experiments successfully reproduced the results of the competitive sorption experiments.

中文翻译：

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碱性条件下钙表面络合和二价阳离子在蒙脱石上的竞争吸附

摘要 在高放废物和超铀废物地质处置系统中，Ca 浓度的增加（由胶结材料的变质引起）会由于竞争吸附而影响其他放射性核素的保留。进行批量吸附实验以研究 Ca 的吸附行为及其与其他二价阳离子（Sr 和 Ni）在碱性条件下 Kunipia F 蒙脱石边缘位点的竞争。Ca 吸附随 pH 值增加（当 pH > 8 时）并且在高离子强度条件下更加明显，表明 Ca 与边缘位点形成了表面络合。Sr 的吸附行为类似于 Ca 的吸附行为。同时，Ni 吸附量随着 pH 值而增加，当 pH 值 >6 时（pH 值低于 Ca 和 Sr 的情况），Ni 比 Ca 和 Sr 更容易形成表面络合物。基于 2 位点质子分解非静电表面络合和阳离子交换 (2SPNE SC/CE) 模型进行的拟合分析结果表明，Ca 和 Sr 吸附在≡SW2OH 位点和 Ni 吸附在 ≡SSOH 位点上。此外，通过阳离子交换对 CaOH+ 和 SrOH+ 离子对物质的吸附暗示在 pH 值 ~ 12 时。还进行了竞争吸附实验以评估 Ca 对 Sr 和 Ni 吸附的影响。在碱性 pH 区域，Sr 吸附随着 Ca 浓度的增加而降低，而 Ni 吸附不受 Ca 浓度的影响。总的来说，这些结果表明 Ca 和 Sr 吸附在相同的位置，而 Ca 和 Ni 吸附在不同的位置；此外，竞争吸附似乎取决于化学相似性（例如 例如，水解行为）。从单元素批量吸附实验中获得的吸附模型参数成功地再现了竞争吸附实验的结果。