Determination of kaolinite floc size and structure using interface settling velocity

Abstract Although interface settling methods are generally simple, they are not used to determine physical properties such as size of flocs because the relationship between the physical properties of a floc during the settling process and its settling velocity is poorly understood. In this study, the interface settling method was extended to soft matter such as kaolinite floc, and a technique was developed to measure the size and diameter of the floc during the settling process using an interface settling method. An equation proposed by Michaels and Bolger, based on the relationship between interface settling velocity and the solid volume concentration of interfering hard spheres as originally developed by Richardson and Zaki, can be applied to soft matter such as clay floc. The present study demonstrated that the effective volume of floc, as well as the diameters of individual floc particles, can be measured by the interface settling method. This was achieved by incorporating the equation for the settling of spheres in a viscous fluid into Michaels and Bolger's settling velocity equation. To investigate the validity of the effective volume and diameter of floc, the diameter and settling velocity were also measured visually. The experimental work in this study involved constructing a device in which soft floc material could settle without interruption, recording the settling with a video camera attached to an optical microscope, and measuring the diameters of individual flocs and their settling velocities from the recorded images. The interface settling method and the optical visualization method provide similar results for the effective volume and the diameter of the floc particles when they are compared at the same pH and the same ionic concentrations. This work demonstrates that the interface settling method is an efficient way to measure the size and diameter of soft matter such as kaolinite floc.