Assessment and Characterization of Mine Waste and Fly Ash Material for Effective Utilization in Opencast Coal Mines

Coal is a major source of nonrenewable energy in India. Most of the Industries depend on the coal to meet the energy demand of the country. Coal mining is invariably associated with the generation of voids. The voids so generated are often filled with overburden (OB) and waste materials. To enhance the utilization, fly ash (FA) is also being used for filling the voids. However, these operations inevitably require excessive planning and control to minimize the environmental impact of mining. In order to evaluate the impact of backfilling the voids with coal mine wastes and fly ash, Overburden and fly ash materials have been collected from Talcher coalfield. The geotechnical characterization study of overburden (OB) sample and OB+30% fly ash samples have been carried out separately for backfilling. After addition of fly ash, it is observed that the permeability is increased but liquid limit, plastic limit, and plasticity index (PI) of the OB are decreased. The maximum dry unit weight of OB mixture decreases while optimum water content increases with the fly ash. The angle of internal friction of OB decreases after addition of the fly ash. Cohesion value of OB sample has not changed much after addition of the fly ash. The grain size analyses results show OB sample is poorly graded. The OB soil type is found to be poorly graded sand of low compressible clay (SP-CL). Similarly, the OB+30% fly ash soil type is of poorly graded sand of low compressible silty (SP-ML) type. The OB and OB+ 30% fly ash contain heavy metals such as Fe and Al in high quantity, mild concentrations of Zn, Cr, and Mn and low amounts of Cu, Co, As, and Se. B and Pb are found below the detection level. The decreasing order of heavy metals in the leachate samples observed to be Fe>Mn>Ni>Cu>Zn>Se>Co>Cd>Cr>As. The major mineral phases in OB and OB+30% fly ash samples are found to be quartz, kaolinite, muscovite, dickite, zinnwaldite, and illite.