Zinc Isotopic Composition of Particulate Matter Generated during the Combustion of Coal and Coal plus Tire-Derived Fuels

Atmospheric Zn emissions from.:he burning of coal and tire-derived fuel (TDF) for power generation can be considerable. In an effort to lay the foundation for tracking these contributions, we evaluated the Zn isotopes of coal, a mixture of 95 wt % coal + 5 wt % TDF, and the particulate matter (PM) derived from their combustion in a power-generating plant. The average Zn concentrations and delta Zn-66 were 36 mg/kg and 183 mg/kg and +0.24 parts per thousand and +0.13 parts per thousand for the coal and coal + TDF, respectively. The (delta Zn-66 of the PM sequestered in the cyclone-type mechanical separator was the lightest measured, -0.48 parts per thousand for coal and -0.81 parts per thousand for coal+TDF. The delta Zn-66 of the PM from the electrostatic precipitator showed a slight enrichment in the heavier Zn isotopes relative to the starting material. PM collected from the stack had the heaviest delta Zn-66 in the system, +0.63 parts per thousand and +0.50 parts per thousand for the coal and coal + TDF, respectively. Initial fractionation during the generation of a Zn-rich vapor is followed by temperature-dependant fractionation as Zn condenses onto the PM. The isotopic changes of the two fuel types are similar, suggesting that their inherent chemical differences have only a secondary impact on the isotopic fractionation process.