Removal of arsenic and metals from groundwater impacted by mine waste using zero-valent iron and organic carbon: Laboratory column experiments

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, SO₄^2-, and acidity in groundwater from an abandoned gold mine. The onset of bacterially-mediated SO₄^2- reduction was indicated by a decrease in Eh, a decline in aqueous SO₄^2- 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.