LEACHING BEHAVIOR AND BIOAVAILABILITY OF ARSENIC AND SELENIUM IN FLY ASH FROM COAL-FIRED POWER PLANTS

A huge amount of fly ash was always produced by coal-fired power plants every year. Arsenic and selenium were absorbed and accumulated in fly ash during the combustion process of coal, but would be released into the environment again when/if fly ash was disposed. To better understand the mobility and bioavailability of arsenic and selenium in fly ash, one sequential extraction procedure was applied to characterize the species of As and Se. Both in fly ash were divided into 5 fractions: water extractable fraction (F1), acid soluble fraction (F2), reducible fraction (F3), oxidable fraction (F4) and residual fraction (F5). The fly ash samples from both the conventional pulverized coal (PC) and the circulating fluidized bed (CFB) combustor were analyzed. The results demonstrated that 71-84% of As and about 96% of Se were present in the extractable fractions (F1+F2+F3+F4) indicating that both in fly ash from coal-fired power plants have high mobility and bioavailability.