Chemical oxidation of selenite to selenate: Evaluation of reactive oxygen species and O transfer pathways
Chemical oxidation of selenite to selenate: Evaluation of reactive oxygen species and O transfer pathways
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DOI：
10.1016/j.chemgeo.2021.120229
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发表时间：
2021-08
期刊：
影响因子：
3.9
通讯作者：
P. Paydary;Alexandra E. P. Schellenger;Minerva Teli;D. Jaisi;A. Onnis‐Hayden;P. Larese-Casanova
中科院分区：
文献类型：
--
作者：
P. Paydary;Alexandra E. P. Schellenger;Minerva Teli;D. Jaisi;A. Onnis‐Hayden;P. Larese-Casanova
天然存在的硒通常存在于页岩中，主要以还原硒化物或元素硒金属的形式存在。相反，下游的含氧沃茨和土壤含有氧化形式的硒，如含氧阴离子亚硒酸盐（HSeO 3-，SeO 32-）和硒酸盐（SeO 42-）。虽然硒化物氧化成硒氧阴离子在O2存在下是可能的，但氧化的实际机制，特别是硒酸盐的形成，还没有完全理解。在这项工作中，活性氧物种进行了评估，在间歇式反应器内的亚硒酸盐氧化在中性pH值。完全亚硒酸盐氧化硒酸盐的臭氧（O3）和次氯酸盐（OCl-，作为阳性对照）分别发生在几分钟和几秒钟内。用过氧化氢将亚硒酸盐部分氧化成硒酸盐需要在2 M H2 O2下反应两周。H2 O2和氧化亚硒酸盐在6 h内完全光催化分解产生羟基自由基。单线态氧，超氧化物，和过氧亚硝酸盐没有观察到氧化亚硒酸盐。通过在氧化实验中使用具有不同δ 18 O同位素组成的亚硒酸盐和H2O，可以推断在硒酸盐形成过程中O的两种不同来源。硒酸盐继承了亚硒酸盐的三个O，并建议通过O转移从这里研究的氧化剂中获得第四个O。
Naturally occurring selenium is usually found in shales, mostly in the form of reduced selenides or elemental selenium metal. In contrast, downstream oxic waters and soils contain the oxidized forms of selenium as the oxyanions selenite (HSeO3−, SeO32−) and selenate (SeO42−). Whereas the oxidation of selenides to selenium oxyanions is possible in the presence of O2, the actual mechanisms of oxidation, and selenate formation in particular, are not fully understood. In this work, reactive oxygen species were evaluated for selenite oxidation within batch reactors at circumneutral pH. Complete selenite oxidation to selenate by ozone (O3) and hypochlorite (OCl−, as a positive control) occurred within minutes and seconds, respectively. Partial oxidation of selenite to selenate by hydrogen peroxide required two weeks reaction at 2 M H2O2. Hydroxyl radicals were generated by photocatalytic decomposition of H2O2and oxidized selenite completely within six hours. Singlet oxygen, superoxide, and peroxynitrite were not observed to oxidize selenite. By using selenite and H2O with varying δ18O isotopic compositions in oxidation experiments, it was possible to infer the two different sources of O during selenate formation. Selenate inherits three O from selenite and is suggested to acquire the fourth O via O transfer from the oxidants studied here.