Nico Peter S, Stewart Brandy D, Fendorf Scott
Earth Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, California 94720, USA.
Environ Sci Technol. 2009 Oct 1;43(19):7391-6. doi: 10.1021/es900515q.
The form of solid phase U after Fe(II) induced anaerobic remineralization of ferrihydrite in the presence of aqueous and absorbed U(VI) was investigated under both abiotic batch and biotic flow conditions. Experiments were conducted with synthetic ground waters containing 0.168 mM U(VI), 3.8 mM carbonate, and 3.0 mM Ca2+. In spite of the high solubility of U(VI) under these conditions, appreciable removal of U(VI) from solution was observed in both the abiotic and biotic systems. The majority of the removed U was determined to be substituted as oxidized U (U(VI) or U(V)) into the octahedral position of the goethite and magnetite formed during ferrihydrite remineralization. It is estimated that between 3 and 6% of octahedral Fe(III) centers in the new Fe minerals were occupied by U. This site specific substitution is distinct from the nonspecific U coprecipitation processes in which uranyl compounds, e.g., uranyl hydroxide or carbonate, are entrapped within newly formed Fe oxides. The prevalence of site specific U incorporation under both abiotic and biotic conditions and the fact that the produced solids were shown to be resistant to both extraction (30 mM KHCO3) and oxidation (air for 5 days) suggest the potential importance of sequestration in Fe oxides as a stable and immobile form of U in the environment.
在非生物间歇和生物流动条件下，研究了在水相和吸附的U(VI)存在时，Fe(II)诱导水铁矿厌氧再矿化后固相U的形态。实验采用含有0.168 mM U(VI)、3.8 mM碳酸盐和3.0 mM Ca2+的合成地下水进行。尽管在这些条件下U(VI)具有高溶解性，但在非生物和生物系统中均观察到溶液中的U(VI)有明显去除。确定去除的U大部分以氧化态的U（U(VI)或U(V)）替代进入水铁矿再矿化过程中形成的针铁矿和磁铁矿的八面体位置。据估计，新形成的铁矿物中八面体Fe(III)中心的3%至6%被U占据。这种位点特异性替代不同于非特异性U共沉淀过程，在该过程中，铀酰化合物，如氢氧化铀酰或碳酸铀酰，被截留在新形成的铁氧化物中。在非生物和生物条件下均普遍存在位点特异性U掺入，并且所产生的固体对萃取（30 mM KHCO3）和氧化（5天空气）均具有抗性，这表明铁氧化物中固存作为环境中U的一种稳定且固定的形式具有潜在重要性。
