Volume 24, Issue 1 (March 2001)
A Laser Technique to Quantify the Size, Porosity, and Density of Clay Clusters During Sedimentation
A technique is developed for measuring the size, porosity, and density of clay clusters (flocs) and the distributions of these fundamental quantities during sedimentation. A laser-particle counter is used to detect cluster size and size distribution. Cluster velocities are computed by taking measurements at successive time intervals. By comparing the initial cluster size distribution with the measured distribution as sedimentation proceeds, a unique relationship between cluster size and settling velocity can be established. By applying a settling model for porous spheres, a unique relationship between cluster diameter and porosity is then established. Cluster density is calculated using fundamental mass-volume relationships. The technique and its working principles are illustrated via two sets of experiments, one for kaolinite clusters in distilled water and another for kaolinite clusters in 0.5 M NaCl. Consistent with double-layer theory, the results show that the porosity of clusters in distilled water is higher than the porosity of clusters in NaCl solution. The results also show that power-law relationships, which state that cluster porosity increases with cluster size, may not be valid for clusters very close to the primary particle size.