Assessment of Metal Pollution of Overburden in a Tropical Coalfield, Ib valley, India: A Case Study

Mining of Coal is one of the chief sources of power generation globally to meet the energy demand. However, the mining operations and power production leads to the generation of overburdens and fly ash in huge quantities. These became severe threat to the environment during backfilling via leaching of contaminants and forming acid mine drainages. To understand the chemical characteristics of overburden, seven locations from the Ib valley coalfield were sampled. Also, a fly ash sample was collected from NTPC, Kaniha, Odisha. Subsequently, laboratory-based experiments were conducted under controlled condition to estimate the leachate characteristics of the overburden and overburden-fly ash (30%) composite samples through various leaching agents viz., distilled water, rain water and 0.1N acetic acid. Overburden samples were found to be slightly acidic in nature, whereas fly ash was almost neutral. The mean concentration of the metals in the OBs showed a decreasing trend of Fe>Al>K>Mg>Ca>Na>Mn>Cr>Cu> Zn> Co>Ni>Cd>Pb. The leachability potential is found to be high with acetic acid followed by rainwater and distilled water. The estimated possible total metal leachate from the 0.1% (0.1219 Million tonnes) of total overburden generated during 2017–18 in Mahanadi coalfields (MCL) was found to be 0.00023%. The results from the metal indices i.e. contamination factor showed that the overburdens are critically contaminated with Se followed by Cd, As and Cu, as their associated shale have quite low values. Also the potential ecological risk (PER) for the overburdens is low if Se, Cd, and Cu are excluded.