Speciation of mercury in coal-fired power station flue gas

Mercury is a potentially toxic trace metal. Mercury exists naturally in coal in very low concentrations, having been incorporated during the coalification process. Consequently, coal-fired power stations are a major anthropogenic source of mercury because of the large quantity of coal used for electricity generation. In the environment, mercury transforms into methylmercury, a potential neurotoxin, bioaccumulates in aquatic biota, and subsequently, enters the food chain. The subsequent environmental fate and ability to capture mercury prior to emission are dependent upon its different physicochemical forms and oxidation states, known as speciation. In this work, speciation of mercury was conducted at five different coal power stations across Australia (one inNewSouth Wales, three inWestern Australia, and one in Queensland) by the Ontario Hydro sampling and analysis method. The totalHgconcentrations in the emissions of these plantswere found to be in the range of 1.9-5.6 μg Nm^-3. Particle-bound mercury Hg^P occurred in very low proportions of 0.3-3.7%, while variable proportions of Hg⁰ and Hg^II were observed. Kinetic calculations were performed assuming a homogeneous system to understand role of the chlorine/mercury ratio of feed coal in the oxidation of mercury during power station combustion. Results from this study are compared to previous work published in the literature and discussed with respect to operating parameters of the power station.