Iron and Arsenic Cycling in Intertidal Surface Sediments during Wetland Remediation

详细信息    查看全文

• 作者：Scott G. Johnston ; Annabelle F. Keene ; Edward D. Burton ; Richard T. Bush ; Leigh A. Sullivan
• 刊名：Environmental Science & Technology
• 出版年：2011
• 出版时间：March 15, 2011
• 年：2011
• 卷：45
• 期：6
• 页码：2179-2185
• 全文大小：938K
• 年卷期：v.45,no.6(March 15, 2011)
• ISSN：1520-5851

文摘

The accumulation and behavior of arsenic at the redox interface of Fe-rich sediments is strongly influenced by Fe(III) precipitate mineralogy, As speciation, and pH. In this study, we examined the behavior of Fe and As during aeration of natural groundwater from the intertidal fringe of a wetland being remediated by tidal inundation. The groundwater was initially rich in Fe²⁺ (32 mmol L^鈭?) and As (1.81 渭mol L^鈭?) with a circum-neutral pH (6.05). We explore changes in the solid/solution partitioning, speciation and mineralogy of Fe and As during long-term continuous groundwater aeration using a combination of chemical extractions, SEM, XRD, and synchrotron XAS. Initial rapid Fe²⁺ oxidation led to the formation of As(III)-bearing ferrihydrite and sorption of >95% of the As(aq) within the first 4 h of aeration. Ferrihydrite transformed to schwertmannite within 23 days, although sorbed/coprecipitated As(III) remained unoxidized during this period. Schwertmannite subsequently transformed to jarosite at low pH (2鈭?), accompanied by oxidation of remaining Fe²⁺. This coincided with a repartitioning of some sorbed As back into the aqueous phase as well as oxidation of sorbed/coprecipitated As(III) to As(V). Fe(III) precipitates formed via groundwater aeration were highly prone to reductive dissolution, thereby posing a high risk of mobilizing sorbed/coprecipitated As during any future upward migration of redox boundaries. Longer-term investigations are warranted to examine the potential pathways and magnitude of arsenic mobilization into surface waters in tidally reflooded wetlands.