New flotation scheme for a difficult-to-float coal using pitch additive in dry grinding

Unlike bituminous coals, lower rank coals are inherently hydrophilic and thus difficult to float with typical oily collectors in moderate additions. The poor floatability of Soma coal was enhanced through a new processing scheme involving dry grinding of coal in the presence of bituminous coal pitch followed by flotation with usual collectors. The floatability of the coal was further improved by heating the coal in the temperature range of 300-600°C. Addition of pitch in dry grinding is found to achieve remarkable increase in recoveries from 22.1 to 89.9 wt% and reduce ash levels from 11.8 to 10.1 wt%. The mechanism of this selective improvement in the hydrophobicity of coal is discussed on the basis of the experimental data.