ENHANCED FLOCCULATION WITH DOUBLE FLOCCULANTS

Flocculation of alumina was investigated in this study with polystyrene sulfonate and cationic polyacrylamide as polymers, alone and in combinations with each other. When used alone, polystyrene sulfonate showed some limited flocculation, while cationic polyacrylamide did not produce any flocculation of the alumina powder. Electrokinetics and adsorption results suggest this to be due to charge neutralization in the former case and electrostatic repulsion in the latter case. When these two polymers were added together, flocculation, measured in terms of settling rate, was enhanced markedly. This is attributed to the bridging by cationic polyacrylamide of alumina particles with preadsorbed polystyrene sulfonate. Viscosity results for the polymer combinations support the governing role of the polymer-polymer complexation. It was also found that flocculation obtained with the two polymers premixed was lower than that obtained with the polymers introduced individually. This suggests that polymer complex formation in bulk during mixing is detrimental to the flocculation process since the interparticle bridging capacity of the polymer is thus reduced.