Use of surfactants to aid the dewatering of fine clean coal

Abstract

Vacuum filtration of clean coal slurries and flocculated slurries with cationic, anionic and nonionic surfactants has been investigated. Significant reductions in filter cake moisture content were obtained for all types of surfactant. The most effective surfactant was CTAB. The final moisture content of filter cakes was reduced from 21 to 11.7 wt% by using a moderate dosage of flocculant followed by surfactant pretreatment. Measurements of electrophoretic mobility, surface tension, adsorption, dewatering kinetics and kinetics of adsorption of surfactants were carried out. A direct correlation exists between the point of zero charge and residual moisture reduction in the filter cake. Test results show that surface tension by itself does not give much indication of the effectiveness of surfactants as dewatering agents. The enhancement in filtration dewatering characteristics has been attributed to the changes that surfactant adsorption causes in the wetting characteristics of the coal surface. (C) 1998 Elsevier Science Ltd. All rights reserved.