Reclamation of Spoil and Refuse Material Produced by Coal Mining using Bottom Ash and Lime

Brazil's coal production is about five million tonnes per year, mostly on open mining operations. Mined land reclamation is difficult due to the high acidity generated by the suphur compounds' oxidation. In order to evaluate the feasibility to use bottom ash and lime for land reclamation of coal mining and processing refuse deposit areas, a field experiment was carried out in a coal waste dumping area over 20 m deep, that was previosly leveled off, located on the Butiá County Recreio mine, in Rio Grande do Sul state, Brazil in 1992 and 1993. Trenches 10m width and 50m length were dug in the coal refuse and filled with bottom ash covered with a layer of soil of different depths. Several summer and winter plant species were grown on 10 × 10 m subplots. A minimum of 0.1 m soil layer over 0.2 m bottom ash with proper liming and fertilization was required to promote plant growth. Low soil pH due to sulphur compounds' oxidation was the most limiting factor for plant growth. Heavy metals Cr, Cd, Ni and Pb concentrations in the plants' shoots were in the range usually determined for plants grown on uncontaminated soils.