Sulfate Availability Drives Divergent Evolution of Arsenic Speciation during Microbially Mediated Reductive Transformation of Schwertmannite

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• 作者：Edward D. Burton ; Scott G. Johnston ; Peter Kraal ; Richard T. Bush ; Salirian Claff
• 刊名：Environmental Science & Technology (ES&T)
• 出版年：2013
• 出版时间：March 5, 2013
• 年：2013
• 卷：47
• 期：5
• 页码：2221-2229
• 全文大小：612K
• 年卷期：v.47,no.5(March 5, 2013)
• ISSN：1520-5851

文摘

The effect of SO₄^{2鈥?/sup> availability on the microbially mediated reductive transformation of As(V)-coprecipitated schwertmannite (Fe₈O₈(OH)_3.2(SO₄)_2.4(AsO₄)_0.004) was examined in long-term (up to 400 days) incubation experiments. Iron EXAFS spectroscopy showed siderite (FeCO₃) and mackinawite (FeS) were the dominant secondary Fe(II) minerals produced via reductive schwertmannite transformation. In addition, 25% to 65% of the initial schwertmannite was also transformed relatively rapidly to goethite (伪FeOOH), with the extent of this transformation being dependent on SO₄2鈥?/sup> concentrations. More specifically, the presence of high SO₄2鈥?/sup> concentrations acted to stabilize schwertmannite, retarding its transformation to goethite and allowing its partial persistence over the 400 day experiment duration. Elevated SO₄2鈥?/sup> also decreased the extent of dissimilatory reduction of Fe(III) and As(V), instead favoring dissimilatory SO₄2鈥?/sup> reduction. In contrast, where SO₄2鈥?/sup> was less available, there was near-complete reduction of schwertmannite- and goethite-derived Fe(III) as well as solid-phase As(V). As a result, under low SO₄2鈥?/sup> conditions, almost no Fe(III) or As(V) remained toward the end of the experiment and arsenic solid-phase partitioning was controlled mainly by sorptive interactions between As(III) and mackinawite. These As(III)鈥搈ackinawite interactions led to the formation of an orpiment (As₂S₃)-like species. Interestingly, this orpiment-like arsenic species did not form under SO₄2鈥?/sup>-rich conditions, despite the prevalence of dissimilatory SO₄2鈥?/sup> reduction. The absence of an arsenic sulfide species under SO₄2鈥?/sup>-rich conditions appears to have been a consequence of schwertmannite persistence, combined with the preferential retention of arsenic oxyanions by schwertmannite. The results highlight the critical role that SO₄2鈥?/sup> availability can play in controlling solid-phase arsenic speciation, particularly arsenic鈥搒ulfur interactions, under reducing conditions in soils, sediments, and shallow groundwater systems.}