Enrichment and particle size dependence of polonium and other naturally occurring radionuclides in coal ash

Coal fired thermal power contributes 70% of power in India. Coal fired power generation results in huge amounts of fly ash and bottom ash of varying properties. Coal, which contains the naturally occurring radionuclides, on burning results in enrichment of these radionuclides in the ashes. In the present study, coal, bottom ash and fly ash samples collected from six coal-fired power plants in India were measured for Po-210 using alpha spectrometry and for natural U, Ra-226, K Th-232 and K-40 by an HPGe gamma-ray spectrometer. Po-210 in fly ash ranged from 25.7 to 70 Bq/kg with a mean value of 40.5 Bq/kg. The range and mean activities of U-238, Ra-226, Th-232, K-40 in fly ash were 38.5-101 (78.1), 60-105.7 (79), 20-125 (61.7) and 43.6 200 (100) Bq/kg respectively. Fly ash and bottom ash contains two to five times more natural radionuclides than feed coal. The results were compared with the available data from earlier studies in other countries. The effect of particle size on enrichment factor of the nuclides in fly ash was studied. Po-210 showed the largest size dependence with its concentration favoring the smaller particle size while Th-232 showed least size dependence. U-238 and Ra-226 showed behavior intermediate to that of Po-210 and Th-232. Also the correlation between sulfur content of the feed coal and activity of Po-210 was investigated. Increased sulfur content in feed coal enhanced enrichment of Po-210 in ash. (C) 2014 Elsevier Ltd. All rights reserved.