Leaching characteristics of metals in fly ash from coal-fired power plant by sequential extraction procedure

A modified sequential extraction procedure was developed and applied to characterize the species of metals in fly ash. Two fly ash samples were collected from a coal-fired thermal power plant located in the north of China. A sample was collected from the conventional pulverized coal (PC) combustor and another from the circulating fluidized bed (CFB) combustor. After extraction by the proposed sequential extraction procedure, the elements in the fly ash samples were divided into a water-extractable fraction (F1), an acid-soluble fraction (F2), a reducible fraction (F3), an oxidizable fraction (F4) and a residual fraction (F5). Except for Cu, V, Cd in the PC sample and V, Zn in the CFB sample, most of the other metals were present in the residual fraction (F5), which was very difficult to release into the environment. The fraction distribution patterns in the two samples were also compared. The results indicated that the distribution of metals in different fractions in fly ash samples were probably impacted by different combustion processes.