Carrier flotation for desulfurization and deashing of difficult-to-float coals

A new concept in carrier flotation has been developed where highly hydrophobic coarse carrier coal particles are coated by slime size, extremely hydrophilic (unfloatable) coal particles of low-rank and the resultant aggregate floated with frother alone. A systematic flotation study in a Denver cell as a function of carrier size, the ratio of carried to carrier and other relevant parameters revealed an optimum carrier size of −0.3 +0.1 mm and a carried to carrier ratio of 0.02. Under the optimum conditions, a fine (−38 μm) concentrate containing 8.3 % ash and 0.72 % total sulfur with a recovery of 81.0 % was obtained from a feed containing 16.3 % ash and 2.0 % total sulfur. The addition of pitch was found to further improve the performance of carrier flotation. The results are explained on the basis of electrostatic forces between the oppositely charged carrier and carried particles and the resultant hydrophobic/hydrophilic balance at the aggregate surface which activates the heterocoagulation of bubble/aggregate cluster.