Acid mine drainage and the associated contaminants, including As and metals, are ongoing environmental issues. Passive remediation technologies have the potential to remove As from mine waste effluents. A series of laboratory column experiments was conducted to evaluate the effectiveness of varying mixtures of organic carbon (OC), zero-valent iron (ZVI), and limestone for the treatment of As, metals, SO42-, and acidity in groundwater from an abandoned gold mine. The onset of bacterially-mediated SO42- reduction was indicated by a decrease in Eh, a decline in aqueous SO42- concentrations coupled with enrichment of δ34S, and the presence of sulfate-reducing bacteria and H2S. Removal of As was observed within the first 3 cm of reactive material, to values below 10 µg L-1, representing > 99.9% removal. An increase in pH from 3.5 to circumneutral values and removal of metals including Al, Cu, and Zn was also observed. Synchrotron results suggest As was removed through precipitation of As-crystalline phases such as realgar and orpiment, or through adsorption as As(V) on ferrihydrite. The results indicate the potential for a mixture of OC and ZVI to remove As from acidic, mine-impacted water.
Keywords: Acid Mine Drainage; Mining; Permeable Reactive Barriers; Water Treatment.
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