Radionuclide transport in brackish water through chalk fractures

WATER RESEARCH

卷:163

Article

Tran, Emily L.¹  Teutsch, Nadya²  Klein-BenDavid, Ofra^3,4  Kersting, Annie B.⁵  Zavrin, Mavrik⁵  Weisbrod, Noam¹ 

[1] Ben Gurion Univ Negev, Jacob Blaustein Inst Desert Res, Zuckerburg Inst Water Res, IL-8499000 Midreshet Ben Gurion, Israel

[2] Geol Survey Israel, 32 Yeshayahu Leibowitz St, IL-9371234 Jerusalem, Israel

[3] Nucl Res Ctr Negev, POB 9001, IL-8419001 Beer Sheva, Israel

[4] Ben Gurion Univ Negev, Geol & Environm Sci Dept, IL-8410501 Beer Sheva, Israel

[5] Lawrence Livermore Natl Lab, Livermore, CA 94550 USA

关键词: Bentonite colloids;    Radionuclides;    Ionic strength;    Carbonate rock;    Fracture flow;   

DOI  :  10.1016/j.watres.2019.114886

来源: Elsevier

【 摘 要 】

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-d) 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 Kd 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. (C) 2019 Elsevier Ltd. All rights reserved.

【 授权许可】

Free