Dissolution of Mn-bearing dolomite drives elevated Cr( vi ) occurrence in a Permian redbed aquifer
Dissolution of Mn-bearing dolomite drives elevated Cr( vi ) occurrence in a Permian redbed aquifer
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含锰白云石的溶解导致二叠纪红层含水层中 Cr(vi) 的出现增加
DOI：
10.1039/d2em00395c
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发表时间：
2022
期刊：
影响因子：
--
通讯作者：
Elwood Madden, Andrew S.
中科院分区：
文献类型：
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作者：
Westrop, Jeffrey P.;Tomlinson, Zachary D.;Maples, Brandon M.;Dee, Kato T.;Swindle, Andrew L.;Elwood Madden, Megan E.;Hu, Qinhong;Elwood Madden, Andrew S.
美国俄克拉荷马州中部的城镇越来越依赖于从中央俄克拉荷马州含水层（COA）取水，因为地表水资源的增长与人口和当前的水需求不成比例。然而，从COA的某些区域抽取的水通常含有高水平的天然存在的六价铬。对诺曼砷测试孔岩心（NATHC）的岩石样品进行了研究，以通过大量矿物学和化学测量、选择性化学提取和微量元素分析来确定Cr的矿物学宿主和Cr（VI）释放机制。结果表明，大多数COA铬包含在铁的氧化物和粘土类质同象取代铁（III）。区域地下水数据的分析，包括层次聚类方法和GIS，表明最强烈的Cr（VI）的发生与钠粘土在深度的阳离子交换。阳离子交换使含锰白云石溶解，从而在原本饱和白云石的地下水中产生锰氧化物。Mn氧化物又已知将Cr（III）氧化成Cr（VI）。在一般情况下，共同存在的含锰碳酸盐和可交换的粘土在任何含水层，特别是那些与铬（III）存在于氧化铁水泥，作为成分的地下水发生的可氧化的微量金属。
Municipalities in central Oklahoma, U.S.A. increasingly rely on water drawn from the Central Oklahoma Aquifer (COA) as surface water resources have not grown in proportion to population and current water demands. However, water drawn from certain regions of the COA frequently contains elevated levels of naturally occurring hexavalent chromium. Rock samples from the Norman Arsenic Test Hole Core (NATHC) were investigated to identify the mineralogic host(s) of Cr and mechanisms of Cr(VI) release via bulk mineralogy and chemistry measurements, selective chemical extractions, and microscale elemental analyses. Results demonstrate most COA Cr is contained in Fe oxides and clays as isomorphic substitutions for Fe(III). Analyses of regional groundwater data, including hierarchical clustering methods and GIS, demonstrate the most intense Cr(VI) occurrence is linked to cation exchange with Na-clays at depth. Cation exchange allows dissolution of Mn-bearing dolomite, which in turn produces Mn oxides in otherwise dolomite-saturated groundwaters. Mn oxides in turn are known to oxidize Cr(III) to Cr(VI). In general, co-occurrence of Mn-bearing carbonates and exchangeable clays in any aquifer, particularly those with Cr(III) present in iron oxide cements, serve as ingredients for groundwater occurrences of oxidizable trace metals.