Oliveira Augusto F, Kuc Agnieszka, Heine Thomas, Abram Ulrich, Scheinost Andreas C
Institute of Resource Ecology Helmholtz-Zentrum Dresden-Rossendorf (HZDR) Forschungsstelle Leipzig, Permoserstr. 15, 04318, Leipzig, Germany.
Theoretische Chemie, Technische Universität Dresden, Bergstr. 66c, 01062, Dresden, Germany.
Chemistry. 2022 Oct 21;28(59):e202202235. doi: 10.1002/chem.202202235. Epub 2022 Sep 23.
The β-emitting Tc isotope is a high-yield fission product in U and Pu nuclear reactors, raising special concern in nuclear waste management due to its long half-life and the high mobility of pertechnetate (TcO ). Under the conditions of deep nuclear waste repositories, Tc is retained through biotic and abiotic reduction of TcO to compounds like amorphous TcO ⋅ xH O precipitates. It is generally accepted that these precipitates have linear (Tc(μ-O) (H O) ) chains, with trans H O. Although corresponding Tc-Tc and Tc-O distances have been obtained from extended X-ray absorption fine structure (EXAFS) spectroscopy, this structure is largely based on analogy with other compounds. Here, we combine density-functional theory with EXAFS measurements of fresh and aged samples to show that, instead, TcO ⋅ xH O forms zigzag chains that undergo a slow aging process whereby they combine to form longer chains and, later, a tridimensional structure that might lead to a new TcO polymorph.
发射β射线的锝同位素是铀和钚核反应堆中一种高产率的裂变产物，由于其半衰期长且高锝酸盐（TcO ）迁移率高，在核废料管理方面引起了特别关注。在深层核废料储存库的条件下，锝通过将TcO 生物还原和非生物还原为诸如无定形TcO ⋅ xH O沉淀之类的化合物而得以保留。人们普遍认为这些沉淀物具有线性（Tc(μ-O) (H O) ）链，其中H O呈反式。尽管已通过扩展X射线吸收精细结构（EXAFS）光谱获得了相应的Tc-Tc和Tc-O距离，但这种结构很大程度上是基于与其他化合物的类比。在此，我们将密度泛函理论与新鲜样品和老化样品的EXAFS测量相结合，结果表明，相反，TcO ⋅ xH O形成之字形链，该链经历缓慢的老化过程，在此过程中它们结合形成更长的链，随后形成三维结构，这可能会导致一种新的TcO多晶型物。
