44 Environmental Geoscience (Posters)

Wednesday, 11 March 2026
9:00 AM - 12:00 PM
RCC, Lower Level Hall

How Flow Conditions affect Metal Sequestration in Iron-(oxyhydr)oxides found in Acid Mine Drainage

Paper number: 44-12
Program: Technical Sessions
Time: 9:00 AM – 9:00 AM

Authors

Abstract

Toxic metals released in acid mine drainage can potentially be re-sequestered during the precipitation of secondary Fe-phases. While the role of Fe-phases in metal sequestration is well documented, there is limited work on how flow conditions (e.g. continuous and intermittent flow, and vernal ponds) impact redox potential, dissolved oxygen, and metal availability, which can influence Fe-oxide transformations and metal uptake. Continuous flow promotes stable, oxidative conditions that favor crystalline Fe-oxides, while intermittent flow causes redox shifts, destabilizing Fe-oxides and triggering adsorption-desorption cycles. Vernal pools enhance metal retention due to limited outflux and reduced oxidation during saturation. The goal of this research is to determine how flow regime can affect the formation of Fe-phases and their ability to sequester metals from an abandoned coal mine in Appalachian Ohio, which contains three sections with different flow conditions: the point source (continuous flow), culvert (intermittent flow) and the flood plain (vernal pool). Aqueous samples (to determine dissolved metal content) and solid samples are taken at each site along a transect from the source through the culvert and floodplain. Sediment samples are analyzed by SEM-EDS for grain-scale composition and morphology and milled for XRF and XRD analyses. A sequential extraction protocol will be used to determine metal speciation. Preliminary results indicate that the sediments near the AMD source are dominated by jarosite and ferrihydrite, with some goethite with an overall composition of up to 70 wt% Fe2O3. Within the culvert, the Fe and S content steadily decrease with a rapid drop in the abundance of jarosite and ferrihydrite, while goethite remains nearly constant. In contrast, samples from the floodplain contained less than 30% Fe2O3 by weight, with nearly no detectable Fe-oxides. Metals exhibited enrichment in the floodplain but not the culvert. Samples from the point source and part-way through the culvert contained aggregates of fine-grained particles (<1–5 µm), with grain size increasing in the culvert and floodplain, with subangular grains ranging from 15 to 30 µm. Metal enrichment in the floodplain is likely due to longer residence times and cycling in Fe-phase crystallinity.

Geological Society of America Abstracts with Programs. Vol. 58, No. 1

doi: 10.1130/abs/2026SE-411586

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