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

A new concept in carrier flotation has been developed where highly hydropho bic coarse carrier coal particles are coated by slime size, extremely hydro philic (unfloatable) coal particles of low-rank and the resultant aggregate d 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 r elevant parameters revealed an optimum carrier size of -0.3+0.1 mm and a ca rried to carrier ratio of 0.02. Under the optimum conditions, a fine (-38 m um) concentrate containing 8.3 % ash and 0.72 % total sulfur with a recover y 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 electrostat ic forces between the oppositely charged carrier and carried particles and the resultant hydrophobic/hydrophilic balance at the aggregate surface whic h activates the heterocoagulation of bubble/aggregate cluster. (C) 2001 Els evier Science Ltd. All rights reserved.