Technetium-99 immobilization in low-temperature nuclear waste forms often relies on additives that reduce environmentally mobile pertechnetate (TcO₄^–) to insoluble Tc(IV) species. However, this is a short-lived solution unless reducing conditions are maintained over the hazardous life cycle of radioactive wastes (some ∼10,000 years). Considering recent experimental observations, this work explores how rapid formation of ettringite [Ca₆Al₂(SO₄)₃(OH)₁₂·26(H₂O)], a common mineral formed in cementitious waste forms, may be used to directly immobilize TcO₄^–. Results from ab initio molecular dynamics (AIMD) simulations and solid-phase characterization techniques, including synchrotron X-ray absorption, fluorescence, and diffraction methods, support successful incorporation of TcO₄^– into the ettringite crystal structure via sulfate substitution when synthesized by aqueous precipitation methods. One sulfate and one water are replaced with one TcO₄^– and one OH^– during substitution, where Ca²⁺-coordinated water near the substitution site is deprotonated to form OH^– for charge compensation upon TcO₄^– substitution. Furthermore, AIMD calculations support favorable TcO₄^– substitution at the SO₄^2– site in ettringite rather than gypsum (CaSO₄·2H₂O, formed as a secondary mineral phase) by at least 0.76 eV at 298 K. These results are the first of their kind to suggest that ettringite may contribute to TcO₄^– immobilization and the overall lifetime performance of cementitious waste forms.

中文翻译：

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通过硫酸盐置换将高tech酸酯固定在钙矾石中。

将Technetium-99固定在低温核废料中通常依赖于将环境可移动的高mobile酸盐（TcO ₄ ^–）还原为不溶性Tc（IV）物质的添加剂。但是，这是一个短暂的解决方案，除非在放射性废物的危险生命周期（约10,000年）内保持降低条件。考虑到最近的实验观察，这项工作探索了如何快速形成钙矾石[Ca ₆ Al ₂（SO ₄）₃（OH）₁₂ ·26（H ₂ O）]，这是一种以水泥废物形式形成的常见矿物，可用于直接形成钙钛矿。固定TcO ₄ ^–。从AB结果算分子动力学（AIMD）模拟和固相表征技术，包括同步辐射X射线的吸收，荧光和衍射法，TCO的支撑成功掺入₄ ^-成经由硫酸盐替代的钙矾石晶体结构通过水性沉淀合成时方法。一个硫酸盐和一种水被替换为一个TCO ₄ ^-和一个OH ^-取代，其中C期间²⁺的取代部位附近配位的水去质子化，以形成OH ^-用于在TCO电荷补偿₄ ^-置换。此外，AIMD计算支持有利的TcO ₄ ^–在298 K时至少在钙矾石中的SO ₄ ^2–处而不是石膏（作为次生矿物相形成的CaSO ₄ ·2H ₂ O）上被0.76 eV取代。这些结果首次表明钙矾石可能有助于TcO ₄ ^–固结性废物形式的固定化和整个生命周期的表现。