Water Quality Impacts from Remediating Acid Mine Drainage with Alkaline Addition

Geochemical and thermodynamic theory predict that metals that occur dominantly as oxyanionic species (e.g., arsenic as opposed to zinc) have reduced mobility in an oxidized environment with iron-rich sediments when the pH is moderately acidic (4.6 to 6.0 s.u.), relative to when the pH is neutral or moderately alkaline (7.0 to 9.0 s.u.). A common objective of remediation of acid mine drainage from abandoned mined lands is increasing the pH through alkaline addition. One predictable result of alkaline addition is the flushing of previously adsorbed oxyanionic metals from the sediments. This release is independent of any additional contribution of the same metals from the alkaline agent that is used. Data from surface water, ground water, leaching tests, and “remediated” mining sites in Appalachia and Midwest basins provide empirical confirmation of the calculations based on theory.