EFFECT OF SURFACE-ACTIVE AGENTS ON FILTRATION AND POST-FILTRATION CHARACTERISTICS OF FINE COAL (SURFACTANTS, CONTACT ANGLE, FLOCCULANT, ZETA POTENTIAL, FROTHER)

The physical cleaning of fine coal by "wet" processes results in slurries containing fine coal suspended in water. An attractive alternative to the thermal drying operation is to remove the water in filter cakes by the use of surface-active chemical reagents. While dispersants are known to reduce the final moisture content in coal cakes, flocculants increase the filtration rate, as well as affect the final moisture content. The effect of frothers and collectors on filtration and post-filtration processes has not been examined in depth and little or no information is available in the literature.;In most cases, three distinct regions were obtained in the adsorption isotherms, characteristic of bilayer formation. The observed complex behavior of the moisture content curves upon filtration/dewatering have been explained on the basis of adsorption of molecules at various concentrations and physical adsorption models as well as reduction of surface tension in the aqueous phase. (Abstract shortened with permission of author.);The effect of two surfactants, a flocculant, a frother and a collector on -32 Mesh coal have been investigated on an individual basis as well as in suitable combinations. The modification of surface properties of coal like adsorption, wettability and zeta potential in the presence of these reagents have been related to filtration and post-filtration characteristics. Surface tension data was used to measure reagent concentration in the aqueous solution. Rate of adsorption studies were also performed. Wettability characteristics were delineated with direct contact angle measurements on coal pellets as well as indirectly obtained by capillary pressure data. The zeta potential of coal slurries in the presence of reagents was measured by the technique of microelectrophoresis. Filtration and dewatering experiments were carried out in a lab-scale unit at 67kPa vacuum for various slurry and reagent concentrations after premixing with powdered coal. Washing phenomena was investigated by using surfactants as wash liquor at various wash ratios and concentrations. The amount of adsorption of wash liquor in filter cakes was also measured.