Pyrite with acid-washed surfaces is chemically inert toward aqueous U(VI) at routine conditions. Given that there is a strong radiation field in the nuclear waste repository, the impact of gamma irradiation on the interaction between aqueous U(VI) and natural pyrite was investigated. Three different natural pyrites, namely Si-, Pb-, and As-pyrites, were used for reactions with uranyl nitrate and uranyl acetate, and the focus was set on Si-pyrite. With an initial pH of ∼ 4.5 and ∼ 6.5, results showed that the solution pH increased mainly due to the reduction of nitrate or the decomposition of acetate caused by the gamma irradiation, while it decreased for the reaction with an initial pH of ∼ 9.0 after gamma irradiation due to the oxidation of aqueous Fe. Meanwhile, significant amounts of U(IV)/U(V) were formed on pyrite surfaces at these three pH conditions, demonstrating that gamma irradiation can greatly enhance the U(VI) reduction by pyrite. We proposed that the oxidizing ·OH radical generated by water radiolysis could react with pyrite, leaving the concomitant e and ·H radicals to be effective reductants for aqueous U(VI) or the U(VI)-precipitate formed on pyrite surfaces. Conversely, the impact of gamma irradiation on the U(VI) reduction is insignificant at pH ∼ 3.0, mainly due to the quenching effect of e by H. Besides, carbonate has an inhibitive effect, because it is a quencher of e and can form anionic complexes with U(VI). The presence of pyrite can also protect UO from γ-irradiation-induced oxidation.

中文翻译：

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通过伽马辐照增强天然黄铁矿表面的 U(VI) 还原

表面经酸洗的黄铁矿在常规条件下对 U(VI) 水溶液呈化学惰性。鉴于核废料处置库中存在强辐射场，研究了伽马辐照对含水 U(VI) 与天然黄铁矿之间相互作用的影响。使用三种不同的天然黄铁矿，即硅黄铁矿、铅黄铁矿和砷黄铁矿，与硝酸双氧铀和乙酸双氧铀进行反应，重点是硅黄铁矿。结果表明，初始pH为~ 4.5和~ 6.5时，溶液pH升高主要是由于伽马辐照引起的硝酸盐还原或乙酸盐分解，而初始pH为~ 9.0的反应后，溶液pH降低。由于铁水溶液的氧化而产生的伽马射线照射。同时，在这三种pH条件下，黄铁矿表面形成了大量的U(IV)/U(V)，表明伽马辐照可以极大地增强黄铁矿对U(VI)的还原。我们提出，水辐射分解产生的氧化·OH自由基可以与黄铁矿反应，使伴随的e和·H自由基成为水相U(VI)或在黄铁矿表面形成的U(VI)沉淀物的有效还原剂。相反，在 pH ∼ 3.0 时，γ 辐照对 U(VI) 还原的影响不显着，主要是由于 H 对 e 的猝灭作用。此外，碳酸盐具有抑制作用，因为它是 e 的猝灭剂，可以形成与 U(VI) 的阴离子配合物。黄铁矿的存在还可以保护 UO 免受 γ 辐照引起的氧化。