The Role of Silicone Surfactants in Coal Dewatering

Abstract

Silicone surfactants are capable of marked lowering of the surface tension of water, superior to that of hydrocarbon-based surfactants. These silicone surfactants are also readily adsorbed at a variety of hydrocarbon/water interfaces. These attributes suggest the use of such surfactants in coal dewatering, an aspect of coal processing that is growing in importance. the interaction of several silicone surfactants based both on the poly(ethylene oxide) (nonionic) and the quaternary ammonium salt (cationic) hydrophile was studied using various coals. Surface tensions, contact angles and zeta potentials were measured. These techniques relate to the three commonly proposed mechanisms for coal dewatering: - i/ Reduced capillary forces caused by aqueous surface tension reduction ii/ Dewetting produced by hydrophobing of the coal iii/ Increased permeability resulting from flocculation of coal particles All of these mechanisms appear to be significant in the dewatering process. Silicone surfactants tend to hydrophilize the coal rather than hydrophobe it. This detracts from the dewatering effect and the best silicone coal dewatering surfactants are those that have adequate surface tension lowering ability without too marked a detrimental water contact angle decrease. Silicone surfactants have only a minor effect on the flocculation aspect. Flocculation is best effected by other materials such as polyacrylamides or silicone polymer emulsions.