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

Abstract

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.