Dissolution of Mn-bearing dolomite drives elevated Cr(vi) occurrence in a Permian redbed aquifer. Issue 12 (15th November 2022)

• Record Type: Journal Article
• Authors: 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.
• Is Part Of: Environmental science. Volume 24:Issue 12(2022)
• Page Start: 2419
• Page End: 2436
• Publication Date: 2022-11-15
• Subjects: Environmental monitoring -- Periodicals; Biological monitoring -- Periodicals; Environmental chemistry -- Periodicals; 363.7363
• DOI: 10.1039/d2em00395c
• Languages: English
• ISSNs: 2050-7887

Abstract

Abstract : Cr(iii ) oxidation and Cr(vi ) occurrence corresponds to regions of cation-exchange induced Mn-carbonate dissolution. Abstract : 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.