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A GEOCHEMICAL EVALUATION OF WEATHERING PROCESSES AND METAL UPTAKE BY VEGETATION IN COAL MINE SPOIL

Abstract Details

2017, BS, Kent State University, College of Arts and Sciences / Department of Chemistry and Biochemistry.
Coal has been a primary resource for energy production throughout the United States, negatively impacting many environments through acid mine drainage (AMD) from underground mines and the weathering of abandoned mine spoil (waste rock) on the land surface. At the Huff Run Watershed in Ohio, ongoing remediation efforts aim to treat point source pollution from legacy mining operations; however, it is not well understood how nonpoint source pollution from the weathering of mine spoil contributes to AMD and how it affects metal cycling in the surrounding vegetation. Our objective was to use flow-through column experiments to model weathering reactions in mine spoil collected from Huff Run Site 25 (HR-25) and to quantify foliar uptake of metals by vegetation growing on mine spoil. Mine spoil was reacted with either a rain water solution, representative of the chemistry of the rain water at HR-25, or with rain water solution enriched with sodium citrate, representative of organic acids that vegetation release from their roots. Effluent solutions from the columns were analyzed to quantify concentrations of metal cations (e.g., Fe, Al, Mn), anions (e.g., SO42-, Cl-), and dissolved organic carbon (DOC). In the rain water column, soluble salts were dissolved and leached out in one pulse near the start of the experiment. DOC initially decreased and then became constant, while effluent pH remained constant at 6.5 over the course of the experiment. In contrast, effluent solutions from the citrate column contained elevated concentrations of solutes that indicate active weathering of the spoil. The leaching of sulfate was constant over time and at a much higher concentration than in the rain water column, potentially indicating oxidation of sulfide minerals. Additionally, the pH of the citrate effluents increased from 6.5 to 8, and the DOC was higher than in rain water effluents and constant, though lower than the influent citrate solution. We propose that citrate may be complexing metal cations in the column and reducing iron oxyhydroxide minerals, e.g., Fe(OH)3, to produce mobile Fe2+ and OH-, thus raising the effluent pH. Citrate oxidation coupled to Fe(OH)3 reduction would release CO2, causing there to be less DOC in the effluents than in the influent solution. The column data also reveal that the reactions in the citrate column may reach steady-state over time. To assess foliar metal uptake (e.g., Al, Mn, Fe, Ca) in vegetation, the green leaves of trees and ground cover vegetation growing on mine spoil were collected, powdered and ashed, and then dissolved in nitric acid. Foliage collected from HR-25 contained high concentrations of Mn and Al, indicating the potential for vegetation to accumulate these elements and slow leaching. However, the Fe foliage concentrations were within nutritional requirements reported for plants. Our results indicate that vegetated mine spoil may experience increased metal mobilization relative to non-vegetated mine spoil due to enhanced chemical weathering by organic acids, and that vegetation may be a potential sink for the mobilized metals Mn and Al, but not for Fe, which then may still be leaching from the mine spoil and contributing to AMD.
Elizabeth Herndon, Dr. (Advisor)
David Singer, Dr. (Committee Member)
David Costello, Dr. (Committee Member)
Alexander Seed, Dr. (Committee Member)
117 p.

Recommended Citations

Citations

  • Frederick, H. E. (2017). A GEOCHEMICAL EVALUATION OF WEATHERING PROCESSES AND METAL UPTAKE BY VEGETATION IN COAL MINE SPOIL [Undergraduate thesis, Kent State University]. OhioLINK Electronic Theses and Dissertations Center. http://rave.ohiolink.edu/etdc/view?acc_num=ksuhonors1494443548705579

    APA Style (7th edition)

  • Frederick, Hannah. A GEOCHEMICAL EVALUATION OF WEATHERING PROCESSES AND METAL UPTAKE BY VEGETATION IN COAL MINE SPOIL. 2017. Kent State University, Undergraduate thesis. OhioLINK Electronic Theses and Dissertations Center, http://rave.ohiolink.edu/etdc/view?acc_num=ksuhonors1494443548705579.

    MLA Style (8th edition)

  • Frederick, Hannah. "A GEOCHEMICAL EVALUATION OF WEATHERING PROCESSES AND METAL UPTAKE BY VEGETATION IN COAL MINE SPOIL." Undergraduate thesis, Kent State University, 2017. http://rave.ohiolink.edu/etdc/view?acc_num=ksuhonors1494443548705579

    Chicago Manual of Style (17th edition)