X-Ray Absorption Near Edge Structure Spectrometry Study of Nickel and Lead Speciation in Coals and Coal Combustion Products

Abstract

The fate and environmental impacts of trace elements from coal fired power stations are a significant concern because of the large quantities of coal used as an energy source. The ultimate environmental fate and health impact of some of these trace elements is dependent on their various forms and oxidation states. Nickel and lead are two of the trace elements classified as “priority pollutants” by the National Pollutant Inventory (NPI) in Australia. This study attempts to understand speciation of nickel and lead in coal and coal combustion products from five coal fired power stations in Australia where bituminous rank coals are utilized. Non-destructive X-ray Absorption Near Edge Structure Spectrometry (XANES) was used to determine speciation of these metals. Semiquantitative speciation of nickel and lead was calculated using a linear combination fit of XANES spectra obtained for selected pure reference compounds. In all fly ash samples, 28−80% of nickel was present as nickel in NiSO4 form, which is a more toxic and more bioavailable form of nickel. Less toxic NiO was detected in fly ash samples in the range of 0−15%. Speciation of lead revealed that 65−70% is present as PbS in the feed coals. In all fly ash samples analyzed, lead comprised different proportions of PbCl2, PbO, and PbSO4. PbCl2 and PbSO4 contents varied between 30−70% and 30−60%, respectively. Chemical reactions resulting in nickel and lead transformation that are likely to have occurred in the post-combustion environment are discussed.