Kaolinite/humic acid interaction in the presence of aluminium ion

The present study concerned the modifications of the interfacial electrical characteristics of a kaolinite clay induced by adsorption of aluminium ions and humic substances. The strong interaction of aluminium ions with clay and humic acids strongly increased the humic acid adsorption. The extent and nature of the kaolinite surface modifications were determined to be functions of the initial doses of kaolinite and humic acids. Weakly complexed humic acids behaved as polyacids and highly complexed humic acids behaved as amphoteric polyelectrolytes. For the latter situation, the anisotropic distribution of positive and negative charges within the adsorbed layer was found to depend on the surface charge of the adsorbent. The ζ potential of kaolinite–aluminium ion–humate complexes depended in a complex manner on all parameters of the system including the initial pH, the area developed by the clay and the volume of the liquid phase, and evolved from negative to positive values with increasing degrees of the relative concentration of aluminium ions and humic acids.