Experimental studies on hydrophobic flocculation of coal fines in aqueous solutions and flotation of flocculated coal

Hydrophobic flocculation of fine bituminous coal particles in aqueous solutions under mechanical conditioning and without any surfactants has been experimentally studied through the measurements of aggregative efficiency, zeta potential and contact angle in this work. The results have shown that the hydrophobic coal fines strongly aggregated in a wide pH range (3.5-9.5), even though the particle surfaces were highly charged. This hydrophobic flocculation closely correlated with particle hydrophobicity, having a stronger aggregation for more hydrophobic coal fines. It reaches the maximum degree only if a sufficient kinetic energy is applied to the coal slurry. Also, it has been found that the hydrophobic flocculation could be greatly enhanced by adding a little amount of nonpolar oil. In addition, the flotation of flocculated coal fines was tested on the fine Prince coal for the deep elimination of ash and pyrite from coals in this work. An ultraclean coal with 1.3% ash remaining was produced with 87% combustible recovery. The ash rejection and pyritic sulfur rejection were about 93% and 66%, respectively.