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A B S T R A C TFly ash was collected from individual mechanical and electrostatic precipitator (ESP) hoppers at a 130-MW pulverized-coal utility unit burning a southeastern Kentucky moderate-to high-S Pennsylvanian Fire Clay coal. The fly ash particle size is generally similar within each row of the mechanical and ESP hoppers, with the mean particle diameter decreasing from >36 μm in the mechanical hoppers to 6 μm in the last ESP row. Rare earth element (REE)-bearing phases occur within fine minerals and, possibly, as part of the fly ash glass phase. Transmission electron microscopy was used to identify Y-Ce-Nd-La-bearing regions within a glassy matrix. Y-and U-bearing zircons were also found in the fly ash. Total REE plus yttrium (REY) occupies a narrow range from 719 to 775 ppm, showing an overall lack of partitioning of the REY elements with respect to particle size and temperature in ash collection systems. The heavy REE increase and the light REE/heavy REE ratio decreases from the mechanical hoppers through ESP rows.

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