Anoxic limestone drains

In 1990, an anoxic limestone drain was installed upstream of a wetland treating acid drainage from another coal-contaminated area of the Fabius Coal Preparation Plant. The total installation cost was approximately 19,000 (D124607, p. 135). 

An anoxic limestone drain is considered a snfticient method of adding alkalinity to acid rock drainage. 

Brodie, G. A., C. R. Britt, T. M. Tomaszewski, and H. N. Taylor. 1991. Use of the passive anoxic limestone drains to enhance performance of acid drainage treatment wetlands. In W. Oaks and J. Bowden, Eds. Proceedings Reclamation 2000 Technologies for Success. Durango, CO, pp. 211-222. 

Naim, R. W., R. S. Hedin, and G. R. Watzlaf. 1991. A preliminary review of the use of anoxic limestone drains in the passive treatment of acid mine drainage. In Proceedings of the 12th Annual West Virginia Surface Mine Drainage Task Force Symposium. Morgantown, WV, pp. 23-38. 

In order to ensure continued neutralization it is necessary to avoid precipitation of blinding minerals on the surface of the alkaline material. This can be avoided if the water is anoxic and ferric iron and aluminium are not present in the water. Anoxic limestone drains are designed to achieve this (Fig. 7). These work by reacting CaCOs with the drainage acidity in an anaerobic environment such that ferric hydroxide precipitation will not occur. If it does then this leads to mantling of the limestone and effectively reduces the efliciency of the drain. This effect occurred at the Cwmstywth drain in central Wales and led to a complete failure of a limestone drain (Fuge 1993). 

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