Effect of heat treatment on the flotation of turkish lignites

Unlike bituminous coals which oxidize upon heat treatment, lower rank coals such as lignites have been found to exhibit improved hydrophobicity on heating. Microflotation tests, zeta potential and infrared measurements have been carried out to understand the flotation behavior of four different lower-rank coals of varying ash and moisture contents. While Yenikoy and Saray coals exhibited improved floatabilily, Alpagut and Soma coals showed either no improvement or adverse effect upon thermal treatment. The zeta potential values of heat treated samples showed drastic changes compared to the original sample. Interaction of anionic and cationic surfactants with the original and heat treated coals was tested to find out their effect on flotation. A quantitative approach was adapted to correlate the flotation response and the quantity of hydrophobic and hydrophilic groups in coal as determined by infrared measurements. It is shown that the amount of hydrophobic and hydrophilic groups in coal dictates whether a particular coal is conductive to thermal treatment prior to flotation.