Polyelectrolytic nature of humic substances aluminum ion complexes - Interfacial characteristics and effects on colloid stability

The present study concerned the modifications of interfacial characteristics of aluminum oxide (hydrophilic substrate) and a polystyrene latex particle (less hydrophilic substrate) induced by adsorption of humic substances, polyacrylamide, hydrolyzed polyacrylamide or polyacrylic acid in the presence of aluminum ions and aimed at determination of the mode of action of humic substances in the colloid stabilization and destabilization. On the basis of electrophoretic mobility measurements, polyacrylamide and hydrolyzed polyacrylamide interact differently with the oxide and synthetic latex particles, whereas humic and polyacrylic acids similarly modify the surface characteristics of the two substrates. The relative concentration of acid groups and aluminum ions determined the electrokinetic potential of the adsorbed layer. The instability domain of the colloidal suspension was found to depend similarly on adsorption time and zeta potential. When the zeta potential ranged between +20 and -20 mV, the domain where positively and negatively charged chain elements coexist, the suspensions became unstable and flocculated rapidly. Excess of complexed positively charged chain segments present at small polymer dosage or dissociated negatively charged chain segments present at high polymer dosage promoted colloid stabilization. (C) 1998 Elsevier Science B.V.