抄録
The volume of sediment composed of flocculated materials is expressed as a function of floc diameter and the number of contacts between flocs. In this expression, the sediment is considered as a randomly packed bed of identical flocs with fractal dimension (D), which is determined by the number of bonds between clusters. The validity of this expression was experimentally tested using a monodispersion of polystyrene latex spheres coagulated with simple electrolytes. In the region near critical coagulation concentration, the formed sediment is characterized by a small effective volume reflecting the extremely small size of flocs composing the sediment. In the region of sufficiently high salt concentration to induce rapid coagulation, bulky sediments made of well-developed flocs are observed. Fairly good agreement between theoretical prediction and experimental result is confirmed for the ultimate sediment volume when experiments are carried out with a low volume fraction of particles. It is found that the volume of the sediment and creaming agree with each other when the absolute value of density difference between the solvent and the particle is the same. This result is an indication that the strength of floc formed with polystyrene latex particles is finite and constant against the ionic strength in the region of rapid coagulation. In order to introduce the factor of floc strength against compaction, we tested the result of scaling analysis on the elastic modulus. The experimental data of the sediment volume versus colloid concentration are found to be consistent with this analysis.
