Influence of Air Contact on the Surface Wettability of Coal and Its Filtration and Flotation Properties

In a laboratory experiment, samples of SS coal prepared in an inert atmosphere (nitrogen) and by standard methods in air are compared. The surface changes of the coal particles are studied by IR spectral analysis and chemical analysis of functional oxygen groups. The wetting properties of the coal are assessed by complementary methods: determination of the limiting wetting angle for a liquid drop; liquid filtration through a layer of coal powder; and reagent flotation. Exposure of the coal surface to air during sample preparation perceptibly changes the function composition and hence the natural hydrophobic properties of the coal particles. The results may be used to refine estimates of the properties of undisturbed coal in beds and to improve methods of sample preparation and coal enrichment and processing.