Coal flotation chemistry

The hydrophobic character of coals of different rank, ranging from lignite to anthracite, was evaluated by contact angle, bubble attachment time, reagentless Hallimond tube flotation response, and the heat of immersion. It was observed that the hydrophobicity and hence floatability first increased with an increase of rank, reached a maximum at an intermediate rank (LVB coal), then decreased with further increase of rank. Using DRIFT- and ATR-FTIR, and XPS spectroscopic techniques, it was shown that coal hydrophobicity depends on the chemical characteristics of the coal surface. Coal hydrophobicity and its rank-dependence can be described by an FTIR spectroscopic criterion--the hydrophilicity index--which contrasts the relative abundance of surface hydrophilic groups OH and COOM with the relative abundance of surface hydrophobic groups ArH and RH. Coal hydrophobicity can also be evaluated by an XPS hydrophobicity index which is the carbon to oxygen ratio in the surface layer of about 20 A.;Increased hydrophobicity/floatability of coals was observed for CO...