Possibilities of Utilization of Aggregates and Extractive Waste from Hard Coal Mining at Janina Mine in the Process of Reclamation of Open-pit Mines

In recent years, the economic importance of gangue mined during coal production has changed and it is currently treated more and more often not as waste but as a source of mineral resources for economic use. The overriding objective throughout the reclamation process of open-pit mines associated with the utilization of external material is to make sure that the placement of waste rock on the surface does not cause damage to the environment. The paper presents results of the diagnosis and evaluation of the possibility of filling open-pit mine workings with mining waste or other materials, for example aggregates produced on the basis of gangue, originating in the Janina Mine mining plant (a subsidiary of TAURON Wydobycie S.A.). The study involved aggregate or coal silts from dewatering on the filter presses. The evaluation refers to the legal aspects and takes the requirements of pollution prevention into account, with a particular emphasis on soil, surface water and groundwater. The analysis of the potential impact on the soil and water environment of the project involving reclamation of the open-pit excavation with the use of minerals or waste from coal mining was carried out based on a study of the total content of sulfur and other elements in the samples pierwiastków (As, Cd, Co, Cr, Cu, Hg, Mo, Ni, Pb, V and Zn), as well as of the leaching of components. Moreover, an examination of the coefficient of permeability and porosity was conducted, which allowed the suitability of the material for the construction of insulating layers to be determined. The physical and chemical analyses were conducted on a total of over a dozen samples of waste rock, a byproduct of the enrichment of coal in the Janina Mine plant. The specific studies of the total sulfur content were conducted for the 16 primary samples scattered into 15 fractions each. Moreover, the so-called secondary samples were created, meaning that fine fractions of less than 20 mm and less than 10 mm were rejected. The total content of the selected components was examined for such crafted samples and their concentrations were determined in the leachable form (batch test 1:10). In the case of use of waste rock as an aggregate for quarry reclamation, a comparative analysis was applied to the legal requirements assigned to the mining waste and the quality of soil and water environment. Based on the conducted studies, it has been concluded that the coal silts (filter cakes) are characterized by good insulating properties and can be used for waterproofing objects, especially in the industrial, communications and mining areas. However, coal silts do not meet the quality requirements, mainly due to their slightly increased chlorides content, in addition to being a waste, which in some cases limits the possibility of their use. The best quality parameters were found for the gangue from the Janina Mine (on the basis of which aggregates are manufactured), but deprived of fine fractions. Physical and chemical analyses of the total content of elements in the secondary samples showed that the obtained values are within the allowable ranges determined by appropriate regulations for the vast majority of samples. The limit of 1% was assumed for the sulfur content. The conducted research on the leaching of pollutants indicates that the tested samples do not introduce contaminants exceeding the limit values for the analyzed metals and sulfates. Only single exceedances of the analyzed parameters are observed. The test results allow to conclude that it is possible to obtain a useful product that meets the requirements of environmental protection, but only after the rejection of fine fractions of the waste material.