Abstract
Contact-angle and flotation techniques were used to evaluate the influence of oxygen — both that inherent in the coal and that introduced by ambient temperature, aqueous oxidation — on a wide range of coal ranks. Oxidation was found to decrease the hydrophobicity and floatability of coal; with the effect being minor for coals of high rank but becoming increasingly important as the rank of coal is reduced. As an approximation, oxidation makes a coal behave as if it were one of lower rank. Frother-only flotation of coal correlates with the captive-bubble contact angle whereas when oil is used as a collector, the flotation appears to follow the pattern shown by the water-sessile drop on a fresh, un-reagentized coal surface. Coal recovery lost through oxidation may often be recovered by use of a variety of collectors, of which No. 2 fuel oil is among the best of those reagents tested. A simple alkali-extraction test may be used to estimate the influence of oxidation on coal-preparation processes and use.
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