The critical parameters affecting neutralization of ferric-iron acid mine waters were characterized by the U.S. Environmental Protection Agency in comparative studies using hydrated lime, rock-dust limestone, and a combination of the two as neutralizing agents. The advantages and disadvantages of each of these neutralizing agents were noted. On the ferric-iron test water, combination limestone-lime treatment provided a better than 25-percent reduction in materials cost as compared to straight lime or limestone treatment. Significant reduction in sludge production was noted by the use of rock-dust limestone and by the use of combination treatment as compared to hydrated-lime treatment. Emphasis on optimizing limestone utilization efficiencies resulted in an increase from approximately 35-percent to 50-percent utilization. Studies using limestone that had been ground to pass a 400-mesh screen resulted in utilization efficiencies near 90 percent.

"Program element no. 1BB040." "June 1974." Report prepared by Mining Pollution Control Branch, Industrial Waste Treatment Research Laboratory, Crown Mine Drainage Control Field Site, Rivesville, West Virginia. Includes bibliographical references (pages 73-75).