Separation of coal macerals

The conditions necessary for efficient, small-scale separation of coal macerals are investigated. The method developed takes advantage of known density differences of the various macerais, but unlike most separations, an isopycnic density gradient centrifugation (DGC) technique is used to isolate pure macerals. The technique consists of grinding the coal in a fluid energy mill to ≈ 3 μm average particle size, separating macerals in an aqueous CsCI density gradient, and analysing the products for maceral composition as a function of density. Excellent separations can be achieved in a single run if the coal is first demineralized and then well dispersed with a wetting agent. Sink-float separations also benefit substantially from the addition of a surfactant. The density gradient centrifugation technique is limited more by inability to liberate macerals from each other on comminution than by any inherent errors in the gradient technique itself. Resolution of pure macerals using the DGC technique is much better than would be obtained from sink-float techniques. Data for three coals of differing constitution are presented.