Effect of Amorphous Fe(III) Oxide Transformation on the Fe(II)-Mediated Reduction of U(VI)
Effect of Amorphous Fe(III) Oxide Transformation on the Fe(II)-Mediated Reduction of U(VI)
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DOI：
10.1021/es101848a
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发表时间：
2011-02-15
影响因子：
11.4
通讯作者：
Waite, T. David
中科院分区：
文献类型：
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作者：
Boland, Daniel D.;Collins, Richard N.;Waite, T. David
最近有报道说，Fe（II）催化的2线水铁矿结晶为针铁矿和磁铁矿可以导致铀的固定。虽然可以预期结晶过程的干扰（例如，硅酸盐的存在）会阻止铀的固定，但这尚未得到证实。在这里，我们提出的结果的X射线吸收光谱研究的命运的六价铀（U（VI））在Fe（E）催化的2线水铁矿和水铁矿共沉淀硅酸盐（硅酸盐-水铁矿）的转变。双线水铁矿单调地转化为针铁矿，而硅酸盐-水铁矿转化为类似于在不存在硅酸盐的情况下合成的水铁矿的形式。U L（III）-边EXAFS数据的建模表明，共沉淀和吸附的U（VI）最初与水铁矿和硅酸盐-水铁矿作为单核双齿表面络合物。在Fe（II）催化的转化过程中，与2线水铁矿相关联的U（VI）被还原，并部分纳入新形成的针铁矿矿物结构，最有可能的U（V），而与硅酸盐-水铁矿相关联的U（VI）没有被还原，并保持在一个类似的形式，其最初的吸附状态。铀（VI），最初吸附到硅酸盐fenihydrate，但是，变得更耐还原溶解表明至少部分减少流动性。这些结果表明，当Fe（H）-催化的类铁矾铁羟基氧化物的转化被抑制时，至少在与这些实验中使用的那些条件类似的条件下，铀还原将不会发生。
It has recently been reported that the Fe(II) -catalyzed crystallization of 2-line ferrihydrite to goethite and magnetite can result in the immobilization of uranium. Although it might be expected that interference of the crystallization process (for example, by the presence of silicate) would prevent uranium immobilization, this has not yet been demonstrated. Here we present results of an X-ray absorption spectroscopy study on the fate of hexavalent uranium (U(VI)) during the Fe(E)-catalyzed transformations of 2-line ferrihydrite and ferrihydrite coprecipitated with silicate (silicate-ferrihydrite). Two-line ferrihydrite transformed monotonically to goethite, whereas silicate-ferrihydrite transformed into a form similar to ferrihydrite synthesized in the absence of silicate. Modeling of U L(III)-edge EXAFS data indicated that both coprecipitated and adsorbed U(VI) were initially associated with ferrihydrite and silicate-ferrihydrite as a mononuclear bidentate surface complex. During the Fe(II)-catalyzed transformation process, U(VI) associated with 2-line ferrihydrite was reduced and partially incorporated into the newly formed goethite mineral structure, most likely as U(V) whereas U(VI) associated with silicate-ferrihydrite was not reduced and remained in a form similar to its initially adsorbed state. Uranium(VI) that was initially adsorbed to silicate-fenihydrite did, however, become more resistant to reductive dissolution indicating at least a partial reduction in mobility. These results suggest that when the Fe(H)-catalyzed transformation of ferrihydrite-like iron oxyhydroxides is inhibited, at least under conditions similar to those used in these experiments, uranium reduction will not occur.