Uranium(VI) Interactions with Mackinawite in the Presence and Absence of Bicarbonate and Oxygen

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• 作者：Tanya J. Gallegos ; Christopher C. Fuller ; Samuel M. Webb ; William Betterton
• 刊名：Environmental Science & Technology (ES&T)
• 出版年：2013
• 出版时间：July 2, 2013
• 年：2013
• 卷：47
• 期：13
• 页码：7357-7364
• 全文大小：460K
• 年卷期：v.47,no.13(July 2, 2013)
• ISSN：1520-5851

文摘

Mackinawite, Fe(II)S, samples loaded with uranium (10^鈥?, 10^鈥?, and 10^鈥? mol U/g FeS) at pH 5, 7, and 9, were characterized using X-ray absorption spectroscopy and X-ray diffraction to determine the effects of pH, bicarbonate, and oxidation on uptake. Under anoxic conditions, a 5 g/L suspension of mackinawite lowered 5 脳 10^鈥? M uranium(VI) to below 30 ppb (1.26 脳 10^鈥? M) U. Between 82 and 88% of the uranium removed from solution by mackinawite was U(IV) and was nearly completely reduced to U(IV) when 0.012 M bicarbonate was added. Near-neighbor coordination consisting of uranium鈥搊xygen and uranium鈥搖ranium distances indicates the formation of uraninite in the presence and absence of bicarbonate, suggesting reductive precipitation as the dominant removal mechanism. Following equilibration in air, mackinawite was oxidized to mainly goethite and sulfur and about 76% of U(IV) was reoxidized to U(VI) with coordination of uranium to axial and equatorial oxygen, similar to uranyl. Additionally, uranium鈥搃ron distances, typical of coprecipitation of uranium with iron oxides, and uranium鈥搒ulfur distances indicating bidentate coordination of U(VI) to sulfate were evident. The affinity of mackinawite and its oxidation products for U(VI) provides impetus for further study of mackinawite as a potential reactive medium for remediation of uranium-contaminated water.