Flocculation of Bentonite Suspension under Suppression of Swelling with Inorganic Electrolyte

Abstract

The flocculation behavior of particles iR two kinds of bentonite suspensions has been studied in the presence and the absence of polymer flocculants. Suspension A was prepared by dispersing bentonite in pure water and subsequent addition of iRorganic electrolytes such as Ca(OH)2 and CaCI2. Suspension B was prepared by dispersing bentonite directly in inorganic electrolyte solution.
Both the settling and the filtration rates of B were higher than those of A. An extreme difference of settling rate was found between A and B, The addition of polymer flocculant greatly increased settling and filtration rates, but the difference in flocculation behavior between A and B still remained. High settling rate (7 cm/min) was obtained with the addition of Ca(OH)2to 250 ppm Ca and Separan NP 20 to 2 ppm in the case of B (Fig, 7),
When kaolin, silica powder, pettery clay or silt rich clay containing no montmorillontite was substituted for bentonite, no appreciable difference was observed in the flocculatioR behavior between two kinds of suspensions. On the other hand, the flocculation behavior of suspensions of coal debris which contained considerable amounts of montmorillonite changed according to the preparation method of suspensions as was the case for bentonite (Fig.2 and Fig.3),
Above experimental results suggest that the addition of an adequate amount of inorganic electrolyte such as Ca(OH)2 to the water for dressing or washing of coal, gravel and the like containing montmorillonite facilitates the flocculation treatment of the waste eMuent from these processes through the resultant suppression of the swelling of montmorillonite.