Chemical Speciation of Fe and Ni in Residual Oil Fly Ash Fine Participate Matter Using X-ray Absorption Spectroscopy

摘要

Epidemiological studies have linked residual oil fly ash fine paniculate matter with aerodynamic diameter <2.5 μm (ROFA PM_(2.5)) to morbidity and mortality from cardiovascular and respiratory illnesses. Bioavailable transition metals within PM have been cited as one of the components that induce such illnesses. By combining synchrotron-based X-ray absorption spectroscopy with leaching experiment, we studied the effect of residual oil compositions and combustion conditions on the speciation of Fe and Ni in ROFA PM_(2.5) and the implication of these species for human health and environment. PM_(2.5) samples were obtained from two types of combustors, a fire tube boiler (FTB) and a refractory line combustor (RLC). The study reveals that only Fe_2(SO_4)_3-nH_2O is present in RLC PM_(2.5) while Fe_2(SO_4)_3·nH_2O predominates in FTB PM_(2.5) with inclusion of varying amounts of nickel ferrite. The finding that RLC PM_(2.5) is more bioavailable and hence more toxic than FTB PM_(2.5) is significant. The reduction of toxicity of FTB PM_(2.5) is due to the immobilization of a portion of Fe and Ni in the formation of an insoluble NiFe_2O_4. This may explain the variation of toxicity from exposure to different ROFA PM_(2.5). Additionally, the speciation data are sought for developing emission inventories for source apportionment study and understanding the mechanism of PM formation.