Coagulation, Sedimentation, and Consolidation of Aqueous Clay Dispersions

Abstract

The existing methods for dewatering sewage sludge containing finely dispersed clay minerals can be applied with an initial moisture content of <75%. In the case of higher moisture content, it is necessary to treat preliminary such dispersions to provide their destabilization, sedimentation, and consolidation, that is, to obtain more concentrated precipitate, followed by the separation of the excess liquid phase. A decrease in the stability of clay disperse systems can be achieved by decreasing the electrostatic repulsion between particles with a decrease in their surface charge due to a change in the pH of the dispersed medium or adsorption of potential-determining cations, as well as due to the compression of the double electric layer with an increase in the total concentration of electrolyte. We studied the effect of the chemical composition of an aqueous dispersed medium on the ζ potential, the interaction and aggregation of dispersed particles in a model system based on kaolinite, sedimentation of aggregates, and consolidation of the sediment. The dependence of the obtained values of the ζ potential on the inhomogeneity of the surface charge of the particles and the polarization of the formed chain aggregates in an electric field is analyzed. The conditions for maximum sediment consolidation are determined, which ensure a further decrease in moisture content using methods combining pressure and electroosmosis.