Floatability and desulfurization of a low-rank (Turkish) coal by low-temperature heat treatment

It is well known that higher rank coals are inherently hydrophobic whereas lower rank coals are more hydrophilic. Because of the hydrophilic character of low-rank coals, they are difficult to float even at high dosages of oily collectors. In the present study, the floatability behavior of a hydrophilic lignitic coal was investigated with and without low-temperature heat treatment using a column flotation and a Denver flotation cell. The floatability and hydrophobicity of the coal were investigated upon heating the coal at 105 °C. After heating it was found that the floatability, hydrophobicity, and separation efficiency of lignite increased dramatically. A change in the hydrophobicity of lignite before and after the low-temperature heating was determined by FTIR spectroscopy. On the other hand, reverse flotation experiments applied in natural, alkaline, and acidic conditions yielded rather good results. A concentrate assaying 1.52% total sulfur was obtained at natural pH from a feed of 2.50% sulfur.