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The hydraulic backfilling of abandoned room and pillar coal mines with ash-based grout holds promise as an environmentally beneficial method of ash disposal, capable of preventing acid mine drainage and subsidence. For this scheme to be economically viable, the grout must be sufficiently flowable so that mines can be filled from a small number of boreholes. This paper describes the development and testing of a water-ash-bentonite grout using ash from a coal and gob burning atmospheric pressure fluidized bed combustor. Bentonite was needed to prevent settling which would limit the ability of the grout to spread. Laboratory techniques were devised to measure the rheological parameters of the grout. A static model was developed to predict the maximum distance of spread due to gravity. A field injection of 765 m3 of grout into an inactive mine panel showed that the grout flows well enough to make hydraulic backfilling feasible.

Abstract. Steel slag leach beds were constructed at the abandoned McCarty mine site in Preston County, West Virginia. The leach beds were constructed as slag check dams below limestone-lined settling basins. Acid water was captured in limestone channels and directed into basins to leach through the slag dams and discharge into a tributary of Beaver Creek. Since installation in October 2000, the system has been consistently producing net alkaline, pH 9.0 water. The water is still net alkaline and has stabilized at a neutral pH after the treated water encounters several other acidic seeps downstream. In addition, other than elevated Cr, which exceeds EPA water criteria for freshwater aquatics at the Beaver pond discharge, metals in the system effluent are within acceptable limits.

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