Vadose-zone alteration of metaschoepite and ceramic UO2 in Savannah River Site field lysimeters.
Vadose-zone alteration of metaschoepite and ceramic UO2 in Savannah River Site field lysimeters.
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DOI：
10.1016/j.scitotenv.2022.160862
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发表时间：
2022-12
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通讯作者：
Connaugh M. Fallon;W. Bower;Brian A Powell;F. Livens;I. Lyon;Alana E. McNulty;K. Peruski;J. Mosselmans;D. Kaplan;D. Grolimund;P. Warnicke;D. Ferreira-Sanchez;Marja Siitari Kauppi;Gianni F. Vettese;S. Shaw;K. Morris;G. Law
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作者：
Connaugh M. Fallon;W. Bower;Brian A Powell;F. Livens;I. Lyon;Alana E. McNulty;K. Peruski;J. Mosselmans;D. Kaplan;D. Grolimund;P. Warnicke;D. Ferreira-Sanchez;Marja Siitari Kauppi;Gianni F. Vettese;S. Shaw;K. Morris;G. Law
二氧化铀（UO2）和偏黄铁矿（UO3•nH2O）颗粒已被确定为核场所的污染物。了解它们的行为和影响对放射性污染土地的安全管理和全面了解铀生物地球化学至关重要。萨凡纳河场地（SRS）（南卡罗来纳州，美国），是一个这样的污染场地，在历史上释放含铀废物到渗透区。在这里，我们使用现场溶析仪（15厘米深x 72厘米长）深入研究了这两种颗粒类型在代表SRS的动态条件下的行为。在每个渗滤仪的两个深度（25厘米和50厘米）放置包含不同颗粒类型的离散层，并暴露于环境降雨中1年，目的是了解动态、浅层地下条件对U颗粒行为和U迁移的影响。1年后，采用沉积物消化、顺序提取、体μ焦点x射线光谱等方法，对颗粒源中铀的溶解和迁移以及溶析仪中铀的形态进行了评估。在uo2溶析仪中，uo2的氧化溶解和随后的U沿水流方向和逆流方向在1 - 2cm范围内的迁移。对uo2源的连续提取表明，它们在1年内发生了显著变化。偏辉长岩颗粒也表现出明显的溶蚀作用，铀向源的迁移略有增强（约几厘米）。然而，在这两个颗粒系统中，释放的U被定量地保留在沉积物中，作为一系列不同的U（IV）和U（VI）相，并且在渗滤仪流出物中没有检测到U。该研究对具有代表性的、与SRS相关的现实条件下的铀颗粒行为提供了有用的见解，并强调了1年内由于与渗透带沉积物的二次反应而导致的铀从颗粒源的有限迁移。
Uranium dioxide (UO2) and metaschoepite (UO3•nH2O) particles have been identified as contaminants at nuclear sites. Understanding their behavior and impact is crucial for safe management of radioactively contaminated land and to fully understand U biogeochemistry. The Savannah River Site (SRS) (South Carolina, USA), is one such contaminated site, following historical releases of U-containing wastes to the vadose zone. Here, we present an insight into the behavior of these two particle types under dynamic conditions representative of the SRS, using field lysimeters (15 cm D x 72 cm L). Discrete horizons containing the different particle types were placed at two depths in each lysimeter (25 cm and 50 cm) and exposed to ambient rainfall for 1 year, with an aim of understanding the impact of dynamic, shallow subsurface conditions on U particle behavior and U migration. The dissolution and migration of U from the particle sources and the speciation of U throughout the lysimeters was assessed after 1 year using a combination of sediment digests, sequential extractions, and bulk and μ-focus X-ray spectroscopy. In the UO2lysimeter, oxidative dissolution of UO2and subsequent migration of U was observed over 1–2 cm in the direction of waterflow and against it. Sequential extractions of the UO2sources suggest they were significantly altered over 1 year. The metaschoepite particles also showed significant dissolution with marginally enhanced U migration (several cm) from the sources. However, in both particle systems the released U was quantitively retained in sediment as a range of different U(IV) and U(VI) phases, and no detectable U was measured in the lysimeter effluent. The study provides a useful insight into U particle behavior in representative, real-world conditions relevant to the SRS, and highlights limited U migration from particle sources due to secondary reactions with vadose zone sediments over 1 year.