Thermal Treatment of Low-Rank Coal and Its Relationship to Flotation Response

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Abstract
The deleterious effect of oxidation processes on coal flotation is generally recognized by researchers in the field. The present study, however, demonstrates that properly controlled low-temperature heating can actually improve coal flotation and its separation from mineral matter especially for low-rank coals. With a lignite sample, low-temperature heating at 130°C for a given time under ambient atmosphere leads to a higher yield and greater ash rejection during subsequent bench-scale flotation experiments. By combining experimental results from Hallimond-tube and bench-scale flotation experiments, bubble attachment-time measurements, wetting phenomena, and FTIR spectroscopy, it is clear that thermal treatment under the above conditions, which involves dehydration and oxidation reactions, changes the coal sample to a more hydrophobic state. These new results provide further evidence of the complexities involved in the analysis of coal surface chemistry as related to flotation phenomena.