Pacific Northwest National Laboratory, Richland, Washington 99353, United States.
University of New South Wales, Sydney New South Wales 2052, Australia.
Environ Sci Technol. 2022 Aug 16;56(16):11857-11864. doi: 10.1021/acs.est.2c02113. Epub 2022 Jul 25.
Characterizing the chemical state and physical disposition of uranium that has persisted over geologic time scales is key for modeling the long-term geologic sequestration of nuclear waste, accurate uranium-lead dating, and the use of uranium isotopes as paleo redox proxies. X-ray absorption spectroscopy coupled with molecular dynamics modeling demonstrated that pentavalent uranium is incorporated in the structure of 1.6 billion year old hematite (α-FeO), attesting to the robustness of Fe oxides as waste forms and revealing the reason for the great success in using hematite for petrogenic dating. The extreme antiquity of this specimen suggests that the pentavalent state of uranium, considered a transient, is stable when incorporated into hematite, a ubiquitous phase that spans the crustal continuum. Thus, it would appear overly simplistic to assume that only the tetravalent and hexavalent states are relevant when interpreting the uranium isotopic record from ancient crust and contained ore systems.
表征在地质时间尺度上持续存在的铀的化学状态和物理赋存状态对于模拟核废料的长期地质封存、准确的铀铅定年以及利用铀同位素作为古氧化还原示踪剂至关重要。X 射线吸收光谱结合分子动力学模拟表明，五价铀被纳入了 16 亿年古老赤铁矿（α-FeO）的结构中，证明了 Fe 氧化物作为废物形式的稳健性，并揭示了赤铁矿在成因年代测定中取得巨大成功的原因。该标本的极端古老性表明，当五价铀被纳入赤铁矿时，其状态是稳定的，而赤铁矿是一种普遍存在的相，跨越地壳连续体。因此，当从古老地壳和所含矿石系统中解释铀同位素记录时，假设只有四价和六价状态是相关的，似乎过于简单化。
