The removal of unburned carbon from coal fly ash by flotation.

Abstract

The purpose of this study is to determine the characteristics and to provide the technical data for the viable economic utilization of coal fly ash by using flotation tests. The main components of the sample are SiO2, Al2O3, and unburned carbon substance, which is enriched in coarse size fractions over 74 μm and under 37 μm is 7.13wt.%. Flotation tests were performed to determine the effects of various flotation parameters including reagents dosage, impeller speed, pulp pH, and grinding time of the test sample using aerofroth 73 (AF 73), pine oil, methyl isobutyl carbinol (MIBC) as frothers and kerosene as a collector. Unburned carbon recovery grew gradually according to the amount of reagents used, however, the flotation tests proved it necessary to improve the liberation of the ash from the unburned carbon fraction of the sample in order to increase the flotation efficiency prior to benecifiation. As the impeller speed increased from 1100 rpm to 1500 rpm, the unburned carbon recovery increased. According to the pH value variations, the unburned carbon recovery improved in the acidic pH range with an optimum at about 3.3. The relationship between the residual carbon content of the sink product and the grinding time indicated that the residual carbon contents tend to decrease as the grinding time increases and when the pH value was adjusted to 3.3, the residual carbon content of the sink product decreased to 0.75 wt.% at 1.6 kg/t of the AF 73 addition used and to 0.5 wt.% at 3.2 kg/t for 30 min of the ground sample.