SIMPLE RELATIONSHIPS AMONG ZETA-POTENTIAL, PARTICLE-SIZE DISTRIBUTION, AND CAKE SPECIFIC RESISTANCE FOR COLLOID SUSPENSIONS COAGULATED WITH FERRIC-CHLORIDE

Kaolinite and latex colloidal suspensions were coagulated with various doses of ferric chloride before being filtered on microfiltration membranes. Subsequent improvements of the filtration rate (7 to 25 times) were observed for small coagulant doses (10 to 20 mg Fe3+/g). The variations of three parameters, the cake specific resistance, the particle interaction energy calculated from zeta potential measurements, and the fraction of colloidal particles remaining in suspension, all showed a minimum at virtually the same concentration of ferric chloride. The fixation of iron ions, which brings positive charges onto the originally negative surfaces, resulted in charge destabilization and aggregation of fines. For the latex, however, overdosing caused the breakup of aggregates and an accordingly lower filtrability. The cake structure was found to be more open at optimum ferric chloride dosage as shown by electron microscopy.