USE OF SURFACTANTS IN FINE COAL DEWATERING

Moisture in coal prior to its utilization is undesirable. Removal of moisture from fine coal (less than 500 microns in size) by filtration and thermal drying contributes heavily to the cost of the clean coal. As an alternative to the thermal drying, the use of surfactants in vacuum filtration was investigated.;The adsorption isotherm of the surfactants exhibited three different regions; characteristic of a bilayer formation. A model for the adsorption isotherm, incorporating the orientation of the surfactant molecules at the surface of the coal particles was proposed. Based on this model the surface area of the coal was found to be 1000 to 2500 m('2)/kg. The observed complex behavior of the moisture content versus the surfactant concentration curve was explained on a consistent basis with the proposed model. An improvement in the dewatering characteristic was observed, whenever the surfactant adsorption made the coal surface hydrophobic. With the anionic Aerosol OT a maximum of 63% reduction in the moisture content of the filter cake was obtained, whereas the nonionic surfactants reduced the moisture content by 40%. However, at the optimum conditions, the adsorption density of Aerosol OT on coal was about four times higher than that of the nonionic surfactants. The amount of DPC adsorbed on coal at the optimum conditions was maximum; being 16 times that of the nonionic surfactants.;The Darcys equation for the flow of two phases through a porous medium, predicted the dewatering curves for the filter cakes formed with the surfactant solution coal slurry reasonably well. The relative permeability of the filtrate through the filter cake was calculated using the capillary pressure desaturation data obtained from the equilibrium experiments.;The effect of cationic (dodecyl pyridinium chloride, Arosurf MG 83A), anionic (Aerosol-OT) nad non-ionic (Triton X-114, Triton X-100) surfactants on the filtration and dewatering characteristics of -32 mesh Pittsburgh seam-Bruceton mine coal was investigated by conducting adsorption, dynamic and equilibrium experiments at various surfactant concentrations. The surfactant concentration was monitored by measuring the surface tension of aqueous solution.