Soil contamination caused by fly ash from coal-fired thermal power plants in India: Spatiotemporal distribution and elemental leaching potential

On combustion, coal produces fly ash (FA) and spheroidal carbonaceous particles (SCP) at high temperatures. Airborne particles like FA and SCP can be transported over long distances by wind, leading to the pollution of air and water resources. Concern mainly arises from various toxic metals loosely bound to the surface of FA and SCP. Here, we trace the provenance of SCP in soil samples collected upwind and downwind from two coal-fired thermal power plants (TPP) in central Nagpur (Khaperkheda and Koradi) that have been operational for over four decades. The samples showed morphological similarities between SCPs from soil samples and FA collected from the Khaperkheda power plant. The SCP distribution shows a sharp increase in the soil profiles coinciding with the expansion of the power plants between 2010 and 2015. Backward trajectories of winds were calculated to ascertain whether the sampling locations downwind of the TPPs were potentially affected by FA emissions. The results from the back trajectories indicate that emissions from the TPP are directed toward the sampling sites. Finally, leaching experiments were conducted in FA to assess the release of elements. Leaching experiments at 30, 40, and 50 degrees C and at a given pH or extraction time did not show any notable differences in elemental concentrations of Al, As, Ca, Cr, Co, Cu, Fe, Mn, Mo, Se, Ni, Ti, V, and Zn. The concentration of different elements mobilized from FA was high at pH 3, with rapid leaching occurring within the first 30 min of the experiment. Hence, disposal, reclamation, and management of FA need to be regulated and monitored correctly to ensure the safety of its use.