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

Kaolinite and latex colloidal suspensions were coagulated with various doses of ferric chloride before being filtered on microfiltration mem branes. Subsequent improvements of the filtration rate (7 to 25 times) were observed for small coagulant doses (10 to 20 mg Fe3+/g). The var iations of three parameters, the cake specific resistance, the particl e interaction energy calculated from zeta potential measurements, and the fraction of colloidal particles remaining in suspension, all showe d a minimum at virtually the same concentration of ferric chloride. Th e fixation of iron ions, which brings positive charges onto the origin ally negative surfaces, resulted in charge destabilization and aggrega tion of fines. For the latex, however, overdosing caused the breakup o f 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.