Iodine speciation in a silver-amended cementitious system
Iodine speciation in a silver-amended cementitious system
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DOI：
10.1016/j.envint.2019.02.070
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发表时间：
2019-05-01
影响因子：
11.8
通讯作者：
Santschi, Peter H.
中科院分区：
文献类型：
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作者：
Kaplan, Daniel I.;Price, Kimberly A.;Santschi, Peter H.
浸银沸石（AgIZ）已被用于从受污染的地下水和核废物流中去除放射性碘，而全世界此类二次废物的存量正在迅速增加。本研究的目的是：1）量化两种水泥浆废物形式对处理使用过的AgIZ的有效性，2）确定水泥浆中包裹的AgIZ浸出的I形态。一个60天的动力学批次实验表明，AgIZ封装在无渣灌浆是非常有效的固定I和银，一种潜在的非放射性致癌物质。然而，AgIZ封装在含矿渣的水泥浆中，这是低放射性废物处置中最常用的水泥浆类型，在固定I方面完全无效。含AgIZ的无渣灌浆仅向接触溶液中释放3.3 μ g/L的总I，而含渣灌浆释放19，269 μ g/L的总I。根据热力学计算，含渣体系的强还原条件（Eh为-392 mV）促进了AgI的还原溶解，生成Ag-（aq）（0）并释放碘离子（I-）到水相中。无渣灌浆系统保持在更氧化的条件下（Eh为439 mV），并从灌浆中释放出最少量的I。在这两种灌浆系统中，最初作为碘化物添加到AgZ中的含水I主要由碘化物和有机I组成，基本上没有检测到碘酸盐。更多的有机-I被检测到在无渣比含渣灌浆系统，因为前者系统的高氧化还原电位更有利于形成氧化的I物种，如I-2，这可能是中间体的I与有机C的共价键在灌浆。碘K边XANES分析表明，在AgIZ-grout样品中，I仅以银碘化物形式存在。总之，这些结果表明，地下灌浆处理的AgIZ废物应在氧化条件下进行，从AgIZ释放的放射性碘可以进行形态转化，对随后的流动性和估计的风险有重要影响。
Silver-impregnated zeolite (AgIZ) has been used for removing radioiodine from contaminated groundwater and nuclear waste streams and the worldwide inventory of such secondary waste is rapidly increasing. The objective of this study was to 1) quantify the effectiveness of two grout waste forms for disposing of the used AgIZ, and 2) determine the I speciation leached from AgIZ encapsulated in grout. A 60-day kinetics batch experiment demonstrated that AgIZ encapsulated in slag-free grout was extremely effective at immobilizing I and Ag, a potential non-radioactive carcinogen. However, AgIZ encapsulated in slag-containing grout, the most common type of grout used for low-level radioactive waste disposal, was entirely ineffective at immobilizing I. While the slag-free grout with AgIZ released only 3.3 mu g/L Itotal into the contact solution, the slag-containing grout released 19,269 mu g/L I-total. Based on thermodynamic calculations, the strongly reducing conditions of the slag-containing system (Eh was -392 mV) promoted the reductive dissolution of the AgI, forming Ag-(aq)(0) and releasing iodide (I-) into the aqueous phase. The slag-free grout system was maintained under more oxidizing conditions (Eh was 439 mV) and a minimal amount of I was released from the grout. In both grout systems, the aqueous I, originally added to the AgZ as iodide, was composed primarily of iodide and org-I, and essentially no iodate was detected. More organo-I was detected in the slag-free than the slag-containing grout system because the high redox potential of the former system was more conducive to the formation of oxidized I species, such as I-2, which may be intermediates in the covalent bonding of I with organic C in grout. Iodine K-edge XANES analysis indicated that I existed exclusively as silver iodide in both AgIZ-grout samples. Together, these results indicate that subsurface grout disposal of AgIZ waste should be done under oxidizing conditions and that radioiodide released from AgIZ can undergo speciation transformations that have important implications on subsequent mobility and estimated risk.