Effects of Increasing Acidity on Metal(loid) Bioprecipitation in Groundwater: Column Studies

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• 作者：Alexander C. Davis ; Bradley M. Patterson ; Michelle E. Grassi ; Blair S. Robertson ; Henning Prommer ; Allan J. McKinley
• 刊名：Environmental Science & Technology
• 出版年：2007
• 出版时间：October 15, 2007
• 年：2007
• 卷：41
• 期：20
• 页码：7131 - 7137
• 全文大小：477K
• 年卷期：v.41,no.20(October 15, 2007)
• ISSN：1520-5851

文摘

Large-scale column experiments were carried out over aperiod of 545 days to assess the effect of increasing acidityon bacterial denitrification, sulfate reduction, and metal(loid) bioprecipitation in groundwater affected by acid minedrainage. At a groundwater pH of 5.5, denitrification andCu²⁺ removal, probably via malachite (Cu₂(OH)₂CO₃)precipitation, were observed in the ethanol-amendedcolumn. Sulfate reduction, sulfide production, and Zn²⁺removal were also observed, with Zn²⁺ removal observedin the zone of sulfate reduction, indicating likely precipitationas sphalerite (ZnS). Se⁶⁺ removal was also observed in thesulfate reducing zone, probably as direct bioreduction toelemental selenium via ethanol/acetate oxidation or sulfideoxidation precipitating elemental sulfur. A step decreasein groundwater pH from 5.5 to 4.25 resulted in increaseddenitrification and sulfate reduction half-lives, migrationof both these redox zones along the ethanol-amended column,and the formation of an elevated Cu²⁺ plume. Additionally,an elevated Zn²⁺ plume formed in the previous sulfatereducing zone of the ethanol-amended column, suggestingdissolution of precipitated sphalerite as a result of thereduction in groundwater pH. As Cu²⁺ passed through thezone of sphalerite dissolution, SEM imaging and EDSdetection suggested that Cu²⁺ removal had occurred viachalcocite (Cu₂S) or covellite (CuS) precipitation.