Over 60 years of nuclear activity have resulted in a global legacy of contaminated land and radioactive waste. Uranium (U) is a significant component of this legacy and is present in radioactive wastes and at many contaminated sites. U-incorporated iron (oxyhydr)oxides may provide a long-term barrier to U migration in the environment. However, reductive dissolution of iron (oxyhydr)oxides can occur on reaction with aqueous sulfide (sulfidation), a common environmental species, due to the microbial reduction of sulfate. In this work, U(VI)–goethite was initially reacted with aqueous sulfide, followed by a reoxidation reaction, to further understand the long-term fate of U species under fluctuating environmental conditions. Over the first day of sulfidation, a transient release of aqueous U was observed, likely due to intermediate uranyl(VI)–persulfide species. Despite this, overall U was retained in the solid phase, with the formation of nanocrystalline U(IV)O₂ in the sulfidized system along with a persistent U(V) component. On reoxidation, U was associated with an iron (oxyhydr)oxide phase either as an adsorbed uranyl (approximately 65%) or an incorporated U (35%) species. These findings support the overarching concept of iron (oxyhydr)oxides acting as a barrier to U migration in the environment, even under fluctuating redox conditions.

中文翻译：

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掺入 U(VI) 的针铁矿的硫化和再氧化：对亚表面氧化还原循环过程中 U 保留的影响

60 多年的核活动导致了受污染的土地和放射性废物的全球遗留问题。铀 (U) 是这一遗留物的重要组成部分，存在于放射性废物和许多污染场地中。U 结合的铁（羟基）氧化物可能为 U 在环境中的迁移提供长期屏障。然而，由于硫酸盐的微生物还原，铁（羟基）氧化物在与硫化物水溶液（硫化物）反应时会发生还原溶解，硫化物是一种常见的环境物种。在这项工作中，U(VI)-针铁矿最初与硫化物水溶液发生反应，然后进行再氧化反应，以进一步了解 U 物种在波动的环境条件下的长期命运。在硫化的第一天，观察到 U 的瞬态释放，可能是由于中间体铀酰 (VI)-过硫化物。尽管如此，整体 U 仍保留在固相中，形成纳米晶 U(IV)O₂在硫化系统中以及持久性 U(V) 组分。在再氧化时，U 与铁（羟基）氧化物相结合，作为吸附的铀酰（约 65%）或合并的 U（35%）物质。这些发现支持铁（羟基）氧化物作为环境中铀迁移屏障的总体概念，即使在波动的氧化还原条件下也是如此。