Chapter 3 - Forces between Clay Particles and the Process of Flocculation

Abstract

This chapter emphasizes forces between clay particles and the process of flocculation. It discusses the basic properties of colloidal suspensions in water, the process of flocculation, the factors affecting flocculation, and some important and frequently encountered definitions. Suspended particles may either repel or attract each other depending on the chemical properties of the solvent. This change from repulsion to attraction indicates the existence of both attractive and repulsive inter-particle forces acting simultaneously on each colloidal particle. The inter-particle forces are essentially secondary bond forces of an electrochemical nature. The origin of the repulsive forces lies in the net electric charge of the sediment particles. Although a soil is electrically neutral, suspended particles may have a negative or positive net electric charge. This charge can readily be demonstrated by applying an electric field to the soil, in which case negatively charged particles move toward the positive electrode and vice versa. This transport is known as electrophoresis.Almost without exception, clay mineral particles carry a negative electric charge on their faces and sometimes a positive charge on their edges. Positive charges occur in ferric hydroxide soils and other metal hydroxide soils. The latter, however, are not of direct importance to cohesive sediment transport mechanics, unless they interfere with the clay minerals themselves.