ADSORPTION OF HUMIC SUBSTANCES BY HYDROXYALUMINUM-MONTMORILLONITE AND HYDROXYALUMINOSILICATE-MONTMORILLONITE COMPLEXES

The interaction between humic substances purified from an Andisol and montmorillonite (Mt) complexed with hydroxyaluminosilicate HAS or hydroxyaluminum (HyA) ions was studied. The HAS ions were formed from solutions containing HyA ions and orthosilicic acid at an Al concentration of 4 mM; Si/Al atomic ratios of 0, 0.25, 0.5, 0.75, and 1.0; and a NaOH/Al molar ratio of 2.0. The adsorption of humic substances by HAS-Mt and HyA-Mt complexes increased as pH decreased in the adsorption systems. The results indicate that besides HyA ions, the reactivity of HAS ions in humus accumulation and the pedogenic implication in soil environments merit attention.