Particle aggregation in complex aquatic systems

The influence of humate, gallate and salicylate on the surface charge character and particle aggregation of permanently and/or conditionally charged clay and oxide minerals (montmorillonite, kaolinite and aluminium-oxide) was investigated at pH 7-8 in the presence of an indifferent electrolyte. pH-dependent surface charging of minerals were determined by acid-base titration. The pH- and ionic strength dependent particle aggregation was measured in both the absence and presence of organic anions by means of dynamic light scattering (DLS). Relatively small amount of organic anions, less than one species per nm(2), adsorbed on the AI-OH surface sites of minerals induces a significant increase in the colloidal stability of dilute suspensions. Bound organic anions smear out the heterogeneity of surface charge and the differences between the clay and oxide minerals. (C) 1999 Elsevier Science B.V. All rights reserved.