The Zuckerburg Institute for Water Research, The Jacob Blaustein Institutes for Desert Research, Ben Gurion University of the Negev, Midreshet Ben Gurion, 8499000, Israel.
Geological Survey of Israel, 32 Yeshayahu Leibowitz St., Jerusalem, 9371234, Israel.
Water Res. 2019 Oct 15;163:114886. doi: 10.1016/j.watres.2019.114886. Epub 2019 Jul 18.
Mobility of radionuclides originating from geological repositories in the subsurface has been shown to be facilitated by clay colloids. In brackish water, however, colloids may flocculate and act to immobilize radionuclides associated with them. Furthermore, little research has been conducted on radionuclide interactions with carbonate rocks. Here, the impact of bentonite colloid presence on the transport of a cocktail of U(VI), Cs, Ce and Re through fractured chalk was investigated. Flow-through experiments were conducted with and without bentonite colloids, present as a mixture of bentonite and Ni-altered montmorillonite colloids. Ce was used as an analogue for reactive actinides in the (III) and (VI) redox states, and Re was considered an analogue for Tc. Filtered brackish groundwater (ionic strength = 170 mM) pumped from a fractured chalk aquitard in the northern Negev Desert of Israel, was used as a solution matrix. Rhenium transport was identical to that of the conservative tracer, uranine. The sorption coefficient (K) of U(VI), Cs and Re, calculated from batch experiments with crushed chalk, proved to be a good predictor of mass recovery in transport experiments conducted without bentonite colloids. A meaningful K value for Ce could not be calculated due to its precipitation as a Ce-carbonate colloids. Transport of both U(VI) and Cs was indifferent to the presence of bentonite colloids. However, the addition of bentonite in the injection solution effectively immobilized Ce, decreasing its recovery from 17-41% to 0.8-1.4%. This indicates that radionuclides which interact with clay colloids that undergo flocculation and deposition may effectively be immobilized in brackish aquifers. The results of this study have implications for the prediction of potential mobility of radionuclides in safety assessments for future geological repositories to be located in fractured carbonate rocks in general and in brackish groundwater in particular.
放射性核素在地下地质储存库中的迁移已被证明是由粘土胶体促进的。然而，在咸水中，胶体可能会絮凝，并起到固定与其相关的放射性核素的作用。此外，对放射性核素与碳酸盐岩相互作用的研究甚少。在这里，研究了膨润土胶体的存在对通过断裂 chalk 传输 U(VI)、Cs、Ce 和 Re 鸡尾酒的影响。进行了有无膨润土胶体的流动通过实验，膨润土胶体以膨润土和 Ni 改性蒙脱石胶体的混合物形式存在。Ce 被用作 (III) 和 (VI) 氧化还原态下反应性锕系元素的模拟物，而 Re 被认为是 Tc 的模拟物。过滤后的咸地下水（离子强度为 170mM）从以色列北部内盖夫沙漠的断裂 chalk 隔水层中抽取，用作溶液基质。铼的迁移与保守示踪剂尿囊素的迁移相同。用粉碎的 chalk 进行批处理实验计算的 U(VI)、Cs 和 Re 的吸附系数 (K) 被证明是在没有膨润土胶体的运输实验中质量回收率的良好预测因子。由于 Ce 沉淀为 Ce-碳酸盐胶体，因此无法计算 Ce 的有意义的 K 值。U(VI)和 Cs 的传输对膨润土胶体的存在无影响。然而，在注入溶液中添加膨润土可有效固定 Ce，将其回收率从 17-41%降低至 0.8-1.4%。这表明与经历絮凝和沉积的粘土胶体相互作用的放射性核素可能会有效地固定在咸含水层中。本研究的结果对于预测未来地质储存库中放射性核素在安全评估中的潜在迁移具有重要意义，这些储存库通常位于断裂的碳酸盐岩中，特别是在咸地下水中。
