SEQUENTIAL EXTRACTION OF PALLADIUM IN FLY ASH FROM COAL-FIRED POWER PLANT

摘要

It was reported that some noble metals including palladium (Pd) were emitted during coal combustion and accumulated in fly ash. Huge amounts of fly ash were produced as a major byproduct by coal-fired power plants every year in the world, but little knowledge about Pd in fly ash was known until now. It was very important to evaluate the levels of Pd in fly ash. The previous studies also indicated that the mobility and bioavailability of elements (or species) were more useful and crucial for environmental risk assessment rather than the total amount. In this paper, not only the total amount of Pd but also its mobility and bioavailability in fly ash were investigated by performing a sequential extraction procedure. The fly ash samples were collected from a coal-fired power plant equipped with both conventional pulverized coal (PC) combustor and circulating fluidized bed (CFB) combustor. High levels of Pd (69.9 μg g~(-1) and 121 μg g~(-1)) were found in the fly ash samples. Pd in fly ash was further characterized as five species operationally by applying a sequential extraction method consisting of 5 extraction steps. From our results, more than 95% of Pd in fly ash was present in the extract-able forms, which meant Pd in fly ash was very active and easy to be extracted in the environment. Pd in fly ash had high mobility and bioavailability, and fly ash produced by power plants was probably a new anthropogenic emission source of Pd.