Study on flotation characteristics of oxidised Indian high ash sub-bituminous coal

It is well known that high rank coals are generally more hydrophobic than low rank coal or oxidised coal. Non-coking coal (sub-bituminous) of the Talcher coal field in India has very high ash content and is believed to have oxidised surface. This coal is very difficult to float even at higher concentration of collector due to its oxidised surface with reduced hydrophobicity. This investigation has been carried out to study the flotation characteristics of oxidised Indian high ash sub-bituminous coal having particle size below 1 mm. Initially the flotation study was carried out using conventional reagents only in a Denver D-12 sub-aeration flotation cell. Then it was pre-treated with aliphatic alcohols i.e., ethanol and butanol to de-oxidise the coal surface. The attempt was also made using a non-conventional reagent known as black oil as promoter for this type of coal to enhance the floatability. The combinations of the above reagents were also studied to improve the flotation performance. Flotation study was also carried out at optimum reagent conditions to evaluate the flotation performance using flotation column. To characterize the flotation performance with respect to maceral's response, the petrography study was carried out on bulk, concentrate, + 500 µm and − 500 µm size fractions of tailings of the flotation. Based on the test data, it may be concluded that this coal has potential to give a product of around 31% ash content with 80.4% yield from 41–42% ash content of feed coal. In case of column flotation, the product ash could be reduced further to 26.6% from the same feed coal with 66.5% yield.