Kinetic study on the sedimentation behavior of Na- and Ca-kaolinite suspension in the presence of polyethyleneimine

Flocculation properties (settling rate, sediment thickness, supernatant clarity) of Na- and Ca-kaolinite suspension have been studied in the presence of cationic polyethyleneimine (PEI) and mixtures of NaCl or CaCl2 with PEI under controlled conditions of pH. Two extreme kinds of qualitative sedimentations have been observed: flocculation–sedimentation (at 0, 10 and 50 ppm PEI) and accumulation–sedimentation (at 200, 600 and 1000 ppm PEI). It is concluded that the highest sediment thickness and lowest turbidity were observed for Na- or Ca-kaolinite suspension at 10 ppm PEI, that is to say the critical flocculation concentration occurred at 10 ppm PEI. The sedimentation behaviors of Na- and Ca-kaolinite suspension in the presence of PEI were found dependent on both pH and nature of electrolytes, while their flocculation was enhanced by the addition of low electrolyte concentration (0.001 mol/l) with PEI (10 ppm).