Much attention has been devoted to developing inexpensive, limestone‐based systems for treating acid mine drainage (AMD) with little or no maintenance. Treatment of AMD with limestone results in a surface coating of metal hydroxides, a process known as limestone armoring. Once armored, limestone is assumed to cease dissolution and acid neutralization. Laboratory and field experiments determined acidity changes in AMD when contacted by armored and unarmored limestone and investigated the implications of armoring on the construction of open limestone channels for treating AMD. Results of a laboratory titration study indicated armored limestone was only 2 to 45% less effective in neutralizing a hydrochloric acid solution as unarmored limestone. A laboratory container study showed that armored limestone was 90% as effective in neutralizing AMD as unarmored limestone. The field study surveyed 2‐ to 8‐yr‐old, rock‐lined channels constructed of sandstone or limestone, and measured water quality changes down the length of the channel. Open limestone channels, though armored, reduced more acidity in AMD (4–62%) than the sandstone channel (2%). The results from open limestone channels were compared to an acid neutralization kinetics model that predicts the rate of acid neutralization for a specified channel size, and AMD flow and acidity concentration. The open limestone channels in the field neutralized more acidity than the model predicted. Open limestone channels show promise for neutralizing AMD in watershed restoration projects and abandoned mine land (AML) reclamation projects where one‐time installation costs are incurred, little to no maintenance is required, and systems do not have to meet specific water quality standards.
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Ziemkiewicz et al. (1997) studied this question.