ABSTRACT
Among mineral commodities of the world, hard coal is extracted in the highest amount (USGS, 2005). Coal is the most important global energy source, providing 26% of the world’s primary energy and 41% of electricity. The top and continuously growing hard coal producer is China with 2549 Mt in 2007, while Poland with declining annual output of 90 Mt holds the eighth position among coal producers, being the biggest hard coal producer in European Union (WCI 2008). The amount of wastes generated and their characteristics depend both on the geologic conditions in the mining area, and on the method of coal extraction. Mechanized mining with shearers results in generation of 30-50% waste with respect to coal output. In Poland, coal mining waste is the largest type bulk waste. In 2007, 39.3 Mt was generated, while 587.5 Mt was stored at dumps (GUS 2008). High extent of coal mining waste re-use, mostly as common fill in engineering construction and for residual coal extraction by physical methods is associated with the re-mining of existing waste dumps and re-deposition of rock material in different conditions that significantly alters pollutants generation, mobilization and migration processes in waste, and adversely affects the aquatic environment, in particular groundwater. Long-term observations in the local ground-and surface water monitoring networks and porewater analysis along the profiles of the re-mined waste dumps, among them the one of the Anna coal mine in Bukow, Poland, showed that coal re-extraction process induces significant alteration in the hydrogeochemical profiles of the dump. A considerable intensification of sulfide decomposition
and sulfate and acidity generation along the profile of a re-disposed layer was observed, at the simultaneous increase of carbonate mineral buffering effect due to increase of their exposure extent, up to the neutralization of the previously acidic mineral. This process was called “waste activation” that resulted from the increase of exposure surface of both acidifying and buffering compounds. It should be anticipated that the observed restoration of the material buffering is only temporary (Szczepan´ska & Twardowska 2004). Redisposed material, besides alteration of distribution and concentration of dissolved constituents in pore solution along the vertical profile of a waste layer, shows also a considerable increase of infiltration water flow rate in the first year of re-disposal and a general increase of contaminant loads, mostly of sulfates, and of iron and manganese migration to the groundwater.
