Studies on ash reduction of a non-coking coal sample by froth flotation

Coal is a vital energy fuel world over, statistically contribution upto 55-60% and it plays a major role in
the economic development of the country. In general Indian coals are poor in quality with high ash
content and they need beneficiation prior to their utilization. CSIR-NML is pursuing dry beneficiation of
non-coking coal for application in DRI, cement and thermal power plant. However, during the crushing of
coal for dry separation, some amounts of ultrafines are generated. There are limitations in treating
ultrafine particles by dry separation methods. To maximise the overall combustible recovery an attempt
was made for ash reduction in a typical non-coking sample from Rajmahal by froth flotation with an
initial target of 25% ash in the product. Kerosene and diesel oil were used as collectors for coal flotation.
The coal sample was characterised thoroughly in terms of petrography characteristics, size analysis and
proximate analysis. Proximate analysis indicated that the coal contains 34.8% ash, 23.52% VM, 6.86%
moisture and 34.82% FC. The coal sample of -150μm was taken for flotation studies. The effect of
important variables such as collector dosage, frother dosage and pH level are investigated for arriving the
optimum value of yield/combustible recovery. Use of dispersant/depressant with diesel oil as collector
was found to give better yield with an ash content of 25% with a combustible recovery of 72%. Efforts
are put in to further reduce ash content in clean coal for metallurgical application.