Issue 12, 2022

Dissolution of Mn-bearing dolomite drives elevated Cr(vi) occurrence in a Permian redbed aquifer

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.

Graphical abstract: Dissolution of Mn-bearing dolomite drives elevated Cr(vi) occurrence in a Permian redbed aquifer

  • This article is part of the themed collection: Geochemistry

Supplementary files

Article information

Article type
Paper
Submitted
27 sep 2022
Accepted
08 nov 2022
First published
09 nov 2022

Environ. Sci.: Processes Impacts, 2022,24, 2419-2436

Dissolution of Mn-bearing dolomite drives elevated Cr(VI) occurrence in a Permian redbed aquifer

J. P. Westrop, Z. D. Tomlinson, B. M. Maples, K. T. Dee, A. L. Swindle, M. E. Elwood Madden, Q. Hu and A. S. Elwood Madden, Environ. Sci.: Processes Impacts, 2022, 24, 2419 DOI: 10.1039/D2EM00395C

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