Effects of anaerobically digested sludge on the oxidation of pyrite and the formation of acid mine drainage

Anaerobically digested municipal sanitary sewage sludge has been mixed with the mine soil at the Palzo Mine, Williamson County, Illinois in an effort to retard the oxidation of the pyrite that is present throughout the mine soil and so decrease the amount of acid mine drainage that forms. To evaluate this treatment, experiments were conducted which examined the oxidation rate of various mixtures of pyrite and sludge as well as each component separately. The experiments show that the oxidation rate is controlled by the pyrite present until a low component ratio of 2 to 1 is reached where the rate drops significantly. Experiments with both treated and untreated mine soil samples showed that treated samples gave Eh and pH values similar to the low ratio mixtures, while the untreated samples had values close to those recorded in the experiments where pyrite dominated the reaction rate. The results of these experiments suggest that the treatment of acid mine drainage producing mine soils with anaerobically digested sludge improves the quality of the drainage on and from the area by causing ferric hydroxide to precipitate and coat the pyrite present and thus prevent the continued oxidation reaction sequence. In this process, sludge ismore » oxidized and must be replaced to hold the conditions on the site stable.« less