Adsorption of humic acid on Ca-montmorillonite

Abstract

Experiment on the adsorption of a calcium · sodium-humate (Ca · Na-HA, Ca2+: Na+; 3.5: 3.4 in molar ratio = HA(D′)) on a Ca-montmorillonite (Ca-Mt) was conducted to analyze the process of adsorption of HA on Ca clays. The adsorption experiment was carried out in solution under conditions whereby a constant (minimum) HA(D′) molecular size was maintained in the dissolved state. The saturated adsorption amount of the HA(D′) monomolecular layer was 20–38 g kg-1at pH 6–7 and in a NaCl concentration range of 0.004-0.028 m. It was concluded that HA(D′) adsorption only takes place on the Ca-Mt edge (E)-surface, because the relations of the adsorption amount vs. pH corresponded to the variation in the electrical potential with the pH of the E-surfaces, and the adsorption amount and the characteristics of these adsorption curves were similar to those of the Na-HA adsorption on Na-Mt. © Taylor & Francis Group, LLC.