Long-Term Settling Characteristics of Some Clays

Abstract

Abstract A series of experiments was set up, the purpose of which was to determine factors affecting long-term settling characteristics of some suspensions of clay-sized materials. Suspensions of approximately 8 g per 1. were prepared using Georgia kaolin, Mississippi bentonite, Wyoming bentonite, Iowa illite and finely ground quartz. In addition, 2 g and 16 g per 1. suspensions of kaolinite were prepared. All suspensions were observed for 2-week periods at constant temperatures of 19°C; kaolinite suspensions were also observed at 2°, 10°, 25° and 31°C. After settling 3–4 days at 19°C, layering formed in all clay suspensions, and all the tops of the layers contained higher concentrations of suspensoid than bottoms. Tops and bottoms of the layers were parallel to liquid top surfaces. At 2°C, no stratification developed in kaolinite suspensions. At 10°C, layering formed only in 2 g per 1. suspensions after 3 months of settling. At higher temperatures, layering formed after 3–4 days of undisturbed settling. Two grams per liter kaolinite suspensions formed five distinct layers; 8 g per 1., nine layers; and 16 g per 1. suspensions formed a many-layered, banded structure after approximately 2 weeks. If layered suspensions were cooled, the layers were not disturbed. However, layering was very responsive to heating: they expanded and tilted downward away from the heat source. With prolonged heating, layering disappeared. These experiments show that temperature and concentration markedly affect long-term settling characteristics of fine-grained suspensions. Layering forms most readily in water with relatively low viscosity and density. If such layered suspensions were formed in nature, such features as graded bedding, lamination, or varving probably would result after complete settling.