Technetium-99 (Tc) contamination remains a major environmental problem at legacy nuclear reprocessing sites, including the Hanford Site (Washington State, USA) where ~700 Ci of Tc has been released into the subsurface. Developing enhanced attenuation and efficient remediation strategies for released Tc requires a complete understanding of retardation processes and Tc mass flux, including the different mechanisms by which Tc is immobilized in the subsurface and the effect of localized subsurface conditions. Selection of over 30 sediments from Hanford waste disposal sites, based on historical information and sediment characterization, for analysis by autoradiography revealed that Tc concentrations were generally below the detection limit of 5 mg Tc/g sediment. When Tc was measurable in vadose zone sediments, it was predominantly present as TcO₄^- in water films associated with fine-grained sediments, with a maximum of 12 % of the total Tc present in the acid-extractable fraction, defined here as the immobile fraction. However, beneath one waste disposal site, where sediments containing minerals with reducing capacity intercepted miscellaneous fission product recovery waste and waste from the bismuth phosphate process, the amount of Tc present in the immobile fraction was 53 % of the total. Characterization of Tc-containing phases present in these field-contaminated sediments for the first time using Tc K-edge X-ray absorption near edge structure spectroscopy revealed that, as well as Tc present as Tc(VII)O₄^- in pore water associated with fine-grained sediments, Tc was also: (i) physically encapsulated within solid phases precipitated from other waste components and in multi-component phosphate minerals; and (ii) present as mixed Tc(VII)/Tc(IV) in localized reducing zones. These results will be used to develop improved long-term Tc remediation strategies optimized for field application, through stimulation of conditions that enhance Tc attenuation.

中文翻译：

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表征地下沉积物中的tech以修复污染物

legacy 99（Tc）污染仍然是遗留核后处理场址的主要环境问题，其中包括汉福德场址（美国华盛顿州），其中约700 CiC的Tc已释放到地下。为释放的Tc开发增强的衰减和有效的补救策略，需要对延迟过程和Tc质量通量有完整的了解，包括将Tc固定在地下的不同机制以及局部地下条件的影响。根据历史信息和沉积物特征，从汉福德废物处置场中选择了30多种沉积物进行放射自显影分析，结果表明Tc浓度通常低于5 mg Tc / g沉积物的检测极限。当在渗流带沉积物中可测量到Tc时，它主要以TcO的形式存在₄ ^-与细粒沉积物相关联，具有最大的锝存在于酸可萃取级分总量的12％，此处定义为不动的分数水的膜。但是，在一个废物处理场的下方，含有降低能力的矿物的沉积物拦截了其他裂变产物回收废物和磷酸铋工艺产生的废物，固定部分中存在的Tc占总量的53％。使用Tc K边缘X射线吸收近边缘结构光谱法首次对这些被田间污染的沉积物中存在的Tc相进行表征，结果表明，以及Tc以Tc（VII）O _{4-的形式存在}^-在与细颗粒沉积物相关的孔隙水中，Tc也是：（i）物理封装在从其他废物成分沉淀的固相和多成分磷酸盐矿物中；（ii）在局部还原区以混合的Tc（VII）/ Tc（IV）的形式存在。通过刺激增强Tc衰减的条件，这些结果将用于开发针对现场应用优化的改进的长期Tc修复策略。