Controls on the Fate and Speciation of Np(V) During Iron (Oxyhydr)oxide Crystallization
Controls on the Fate and Speciation of Np(V) During Iron (Oxyhydr)oxide Crystallization
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DOI：
10.1021/acs.est.5b05571
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发表时间：
2016-04-05
影响因子：
11.4
通讯作者：
Morris, Katherine
中科院分区：
文献类型：
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作者：
Bots, Pieter;Shaw, Samuel;Morris, Katherine
在一系列体系中，探讨了铁水合石结晶成赤铁矿和针铁矿过程中镎作为Np(V)O-2（+）的形态和归宿。NpO2+对铁（III）（氧）氧化物相的吸附是可逆的，对于水合铁，通过形成单核双齿表面配合物发生。化学萃取和x射线吸收光谱（XAS）分析表明，在铁水合物（pH 10 5）结晶过程中，Np(V)进入赤铁矿结构，这是通过Np(V)在海王星状配位中直接取代八面体配位的Fe（III）而发生的。对针铁矿和赤铁矿混合结晶产物（pH分别为9.5和11）的分析表明，Np(V)在结晶过程中被掺入。相反，在极端pH为13.3时，针铁矿结晶过程中Np(V)掺入的证据有限。这可能是由于形成了一种Np(V)氢氧化物沉淀，防止掺入针铁矿颗粒。总的来说，这些数据突出了Np(V)在铁（III）（氧合）氧化物结晶过程中的复杂行为，并证明了镎掺入环境重要矿物相的明确证据。这扩大了我们对地球化学条件范围的了解，在这些条件下，放射性毒性Np在自然和工程环境中有可能长期固定。
The speciation and fate of neptunium as Np(V)O-2(+) during the crystallization of ferrihydrite to hematite and goethite was explored in a range of systems. Adsorption of NpO2+ to iron(III) (oxyhydr)oxide phases was reversible and, for ferrihydrite, occurred through the formation of mononuclear bidentate surface complexes. By contrast, chemical extractions and X-ray absorption spectroscopy (XAS) analyses showed the incorporation of Np(V) into the structure of hematite during its crystallization from ferrihydrite (pH 10 5) This occurred through direct replacement of octahedrally coordinated Fe(III) by Np(V) in neptunate-like coordination. Subsequent analyses on mixed goethite and hematite crystallization products (pH 9.5 and 11) showed that Np(V) was incorporated during crystallization. Conversely, there was limited evidence for Np(V) incorporation during goethite crystallization at the extreme pH of 13.3. This is likely due to the formation of a Np(V) hydroxide precipitate preventing incorporation into the goethite particles. Overall these data highlight the complex behavior of Np(V) during the crystallization, of iron(III) (oxyhydr)oxides, and demonstrate clear evidence for neptunium incorporation into environmentally important mineral phases. This extends our knowledge of the range of geochemical conditions under which there is potential for long-term immobilization of radiotoxic Np in natural and engineered environments.