Electrokinetic clarification of colloidal suspensions

A novel apparatus has been developed for the electrophoretic clarification of concentrated colloidal suspensions. The laboratory equipment is capable of being scaled up to much larger capacity. The apparatus was designed to process suspensions in either batch or semicontinuous operation, and it has been used to demonstrate the removal of coal/clay colloidal matter from the effluent of a coal-washing facility. In addition, a parametric study of sodium-bentonite suspensions in batch operation was performed to elucidate the effects of initial colloid and electrolyte (NaCl) concentrations on the rate of clarification and the instantaneous power requirements. It was found that an increase in either the initial particle or electrolyte concentration (up to 50 mg of NaCl/L) caused a decrease in the instantaneous power levels but increased the time necessary to reach a given solution clarification. Typical electrophoretic clarification experiments resulted in 99.9% removal of the colloidal matter. In semicontinuous operation it was shown that a 0.2 wt % sodium-bentonite suspension could he clarified to 2.6 x 10(-4) wt % in 13.5 h without the addition of flocculants or other chemicals.