Disposal of Acid Drainage Generating Mine Tailings in Lakes and Man-Made Reservoirs

A simple model is proposed to predict the rate of oxidation if acid mine tailings were disposed on the bottom of a meromictic pit near Mattabi mine near Ignace, Ontario, Canada. We assume the oxidation of pyrite establishes the rate of acid liberated for a given amount of oxygen consumed by the tailing. Acid generation is however independent of the amount of impounded tailings because the oxygen flow is limited by tranquil diffusion through the hypolimnion and is solely a function of depth and morphometry of the water body. Using the standard acid-base accounting method the model also predicts the amount of calcite equivalent needed to neutralize the generated acid and how long a given load of calcite would last. Based on their composition, Matabi tailings already have the acid equivalent of at most 96 g of calcite per Kg of tailing. If the pit was filled with this tailings to a depth of 16 m the calcite in the tailings would be able to neutralize the generated acid for a period of several thousand years. The impoundment of tailings thus appears to be a practical and feasible technique for environmentally-safe disposal as long as the meromictic character of the pit can be maintained.