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Controls on pH and Pyrite Oxidation Pathways across the Phreatic Surface of a Coal Waste Deposit in Southwest Indiana

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dc.contributor.author Hardisty, D.S.
dc.contributor.author Olyphant, G.A.
dc.contributor.author Pratt, L.M.
dc.date.accessioned 2010-07-27T18:45:34Z
dc.date.available 2010-07-27T18:45:34Z
dc.date.issued 2010-06
dc.identifier.uri http://hdl.handle.net/2022/8996
dc.description This presentation was given at the 2010 Annual Meeting of the American Society of Mining and Reclamation, Pittsburgh, PA, June 5-10, 2010. en
dc.description.abstract During acid mine drainage (AMD) generation, the factors controlling pH and pyrite oxidation can differ between the saturated and unsaturated zones. These differences, however, may not always be considered during field-scale remediation efforts. At an unreclaimed coal waste deposit in southwest Indiana, preliminary studies have identified a horizontal pH gradient that increases from 2.8 to 6.5 along a 90 meter shallow groundwater flow path. This site provides a unique opportunity to determine pyrite oxidation pathways under varying conditions within both the saturated and unsaturated zones of coal mine refuse being subjected to weathering processes. Vertical profiles of pore-water were obtained using Diffusion-Controlled Dialysis Membrane Samplers installed across the phreatic surface. Samples were collected at 2 cm intervals from the ground surface to a depth of 40 cm with the bottom 10 cm being fully saturated. Samples collected during the summer reveal a linear trend with respect to pH and depth with pH values of approximately 2.5 near the surface to 3.4 at the base of the profile. Concentrations of sulfate (SO42-) and iron (Fe-total) during the summer are highest near the surface and in the case of Fe, decrease by an order of magnitude at the bottom of the profile. Samples collected during the autumn show that within the saturated zone, ferrous iron (Fe2+) concentrations are elevated relative to ferric iron (Fe3+), but Fe3+ increases with decreasing pH. This indicates that atmospheric oxygen is the limiting factor in pyrite oxidation both through direct oxidation of pyrite and through the oxidation of Fe2+ to Fe3+ that can then oxidize pyrite in both saturated and unsaturated conditions at lower pH values. These results imply that an increase in the thickness of the saturated zone can act as a control on acidity generation by preventing positive feedback cycling of Fe3+ to oxidize pyrite. en
dc.language.iso en_US en
dc.rights This work is licensed under the Creative Commons Attribution-NonCommercial-ShareAlike 2.5 License. To view a copy of this license, visit http://creativecommons.org/licenses/by-nc-sa/2.5/ or send a letter to Creative Commons, 543 Howard Street, 5th Floor, San Francisco, California, 94105, USA. en
dc.rights.uri http://creativecommons.org/licenses/by-nc-sa/2.5/ en
dc.subject coal en
dc.subject reclamation en
dc.subject Indiana Geological Survey en
dc.subject Indiana en
dc.subject pyrite en
dc.subject AMD en
dc.subject acid mine drainage en
dc.title Controls on pH and Pyrite Oxidation Pathways across the Phreatic Surface of a Coal Waste Deposit in Southwest Indiana en
dc.type Presentation en


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This work is licensed under the Creative Commons Attribution-NonCommercial-ShareAlike 2.5 License. To view a copy of this license, visit http://creativecommons.org/licenses/by-nc-sa/2.5/ or send a letter to Creative Commons, 543 Howard Street, 5th Floor, San Francisco, California, 94105, USA. This work is licensed under the Creative Commons Attribution-NonCommercial-ShareAlike 2.5 License. To view a copy of this license, visit http://creativecommons.org/licenses/by-nc-sa/2.5/ or send a letter to Creative Commons, 543 Howard Street, 5th Floor, San Francisco, California, 94105, USA.

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