Intrinsic characteristics of coal combustion residues and their environmental impacts: A case study for Bangladesh

This study has focused on petrography, geochemistry, radiochemical, and leaching properties of coal combustion residues (CCRs), their leachates and nearby waters from the Barapukuria coal-fired power-plant (BCPP) to evaluate the potential environmental impacts and human health hazards for the first in Bangladesh. The CCRs, used in this study are predominantly comprised of Al-Si-rich glassy materials (94.8%) followed by crystallites (3.6%), notably quartz, mullite, and spinel with rock-fragments (0.3%); and un-burnt organic constituents (1.3%) such as anisotropic coke (0.8%) and slightly altered inertinite (0.5%). Hematite, magnetite, cristobalite, monazite, zircon, rutile, tourmaline and sillimanite were also identified as trace minerals. Elemental contents are found to be elevated (2.1–14.2 times) in the fly ash (FA) and bottom ash (BA), as compared to world coal-ash average with the exceptions of Ni in FA; and of Zn, As, Cu, and Hg in BA. The sum of detected rare earth elements is significantly high as compared to the world FA, Indian and Chinese ash residues. The specific activities of CCR are comparatively higher by a factor of 3.7 (²²⁶Ra) to 6.2 (²³²Th) than those of the world average. The examined spheres, particles, and agglomerates of FA are predominantly comprised of C, Al, and Si as major while, K, Ca, Mg, Fe, W and Ti as minor elements. On the other hand, extractable amounts of soluble potentially toxic elements in FA leachates are 7.7% for Se, 4.8% for Zn, and in BA 5.7% for As and 3.1% for Se and others are < 1%. Metals are substantially released from FA in the range of 8.5 (for Cr) to 9650 (for Zn) ppb and 0.002% (for Cr) −7.7% (for Se), while from BA below detection level (for Cr) to 940 ppb (for Mn). The concentration of hazardous metals in the discharged waste water and water ash pond were higher than those were found in nearby pond- and ground-water sources around the BCPP. Ecological and radiological risk indices suggest moderate-risk derived from FA and low-risk from BA.