| Numerous methods have been devised to address the adverse environmental impacts associated with acid mine drainage (AMD). These developments have historically relied on control devices or “active treatments” that fall short of addressing the problem; more recent treatment strategies have involved passive systems. Alkaline generating “wetlands” and anoxic limestone drains (ALDs) are two passive treatments that have received considerable attention. With respect to underground mines, a more functional approach maybe the amelioration of AMD through treatment with alkaline coal combustion by-products (CCBs). Groundwater and infiltrating surface water collect within the mine workings to form pools or reservoirs of AMD. If these pools can be treated in situ, then the adverse impacts associated with the discharge water can be minimized or prevented.; The goal of this research was to determine how to effectively treat AMD in situ using CCBs and to develop a better understanding of the chemical and physical processes involved with the treatment. AMD treatment within the mine was investigated through laboratory research and field demonstration.; The laboratory investigation evaluated the physical and chemical properties of three alkaline CCBs to determine their effectiveness in an AMD treatment scenario. The laboratory investigation focussed on three types of CCBs and one synthetic mine drainage. The laboratory portion identified theoretical treatment considerations and which materials were best suited for treatment in a field setting.; The field study demonstrated the effectiveness of in situ treatment of AMD. The goal of this treatment was to create a highly alkaline buffering zone inside the mine. The demonstrated treatment method involved the injection of 418 tons of FDA into an acidic (pH = 4.4), flooded mine void. Once injected, alkalinity from the FBA was imparted to the system, which neutralized the existing acid and increased the pH. With elevated pH levels, metal species precipitated within the mine as hydroxides and carbonates. Consequently, the AMD after injection had an elevated pH, increased alkalinity, and a reduced metals load.; However, the amount of alkalinity introduced in the field study proved to be insufficient to treat the discharge to Federal standards and provided only temporary benefits. Despite these limitations, the technology proved to be very successful at mitigating some of the adverse effects associated with AMD. Given the complex and uncertain conditions that are typically observed at abandoned underground mine sites, alkaline injection may not be feasible in all situations. Based on the chemical improvements observed in the mine water, in situ treatment may prove to be beneficial as a preliminary treatment for passive systems, such as ALDs and wetlands.; Two benefits were achieved by this research. First, a better understanding of the chemistry associated with the treatment was developed through laboratory study. Second, the field study achieved significant changes in mine water quality. Further laboratory and field research is needed to improve the treatment (more metals precipitation and longer treatment) and reduce uncertainty related to the fate of the introduced alkalinity. If this is done, it is anticipated that in situ CCB injection will become a useful fullscale treatment method. (Abstract shortened by UMI.)... |
