Abstract: Adsorption experiments were conducted by mixing homoionic kaolinite and C14-labeled hydrolyzed polyacrylonitrile (HPAN) in water and solutions of electrolytes. Langmuir type adsorption isotherms resulted. Exchange cations on kaolinite increased adsorption in approximately the same order as such cations reduce zeta potential, i.e. Th4+ >Ca2+ >Ba2+ >H+ > NH 4 + >K+ >Na+. The anomalous increase in adsorption in the presence of polyvalent exchange cations suggested adsorption at the site of base exchange salt formation. Sorbed anions increased adsorption of HPAN in the order of electronegativity, i.e. F− >OH− > H 2 PO 4 − >Cl− >CH3COO− > NO 3 − .
An increase in the concentration of electrolyte and acidity of the adsorbate medium increased adsorption of HPAN. This effect was apparently due to the reduction of electrostatic repulsion between HPAN and kaolinite and a reduction in size of the polymer coil. Divalent cations, especially the transition metals capable of being complexed by HPAN, were more effective than univalent cations. Dissolution of the clay lattice caused desorption of HPAN.
HPAN adsorption reduced the intensity of the OH and O—Al—OH bands in infrared absorption spectra of the kaolinite. Preadsorption of aurintricarboxylic acid blocked adsorption of HPAN, suggesting that “positive spots” due to exposed lattice aluminum on edges of the clay platelets were adsorption sites.