A METHOD FOR PREDICTING THE ALKALINITY GENERATED BY ANOXIC LIMESTONE DRAINS

A method has been developed to predict the alkalinity generated by anoxic limestone drains (ALDs) using a specific mine water and a selected limestone material. Collapsible, 3.8-liter (1.0 gal) containers were loaded with. limestone, filled with untreated mine water, and the generation of alkalinity was monitored by periodic extraction of water samples. In order to determine the predictive capabilities of this method, tests were conducted at two ALD sites where samples of untreated mine water were available. After two days of contact between untreated water and limestone, mean alkalinity concentrations within the experimental containers were within 6% of the actual alkalinity concentrations in the respective ALD effluents. This experimental method was used to compare alkalinity generation of seven carbonate rocks with differing compositions and two different mine waters. Generation of alkalinity within the experimental containers was similar for all of the limestones tested within each of the mine waters. Dolomite generated significantly less alkalinity than limestone. After two days of contact between mine water and carbonate rock, dolomite generated only 50 percent of the alkalinity that was generated by limestone. The two mine waters generated significantly different alkalinity concentrations in the experimental containers containing the similar limestones indicating that the chemistry of the untreated mine water plays an important role in alkalinity generation.