Adsorption of Polycations on Clays: A Comparativein situStudy Using133Cs and23Na Solution Phase NMR

Abstract

23Na solution phase NMR has been evaluated as anin situprobe to study the adsorption of tetramethylammonium (TMA+) and two polycations, FL17 ([(Me2NCH2CHOHCH2)n]n+Cln) and Magnafloc 1697, ([(CH2CHCH2N(Me)2CH2C̄HCH2)n]n+Cln), onto clays in aqueous suspensions containing 2.5 mass% low iron Texas bentonite. The NMR data shows the effectiveness of the organocations at displacing Na+from the bentonite surface. This information has been correlated with that obtained from particle-size and electrophoretic measurements in aqueous solution, together with information from adsorption isotherms. These results have been compared to those obtained in parallel studies using133Cs solution phase NMR. FL17 and 1697 both exhibited high affinity adsorption isotherms on Na+- and Cs+-clay, whereas the adsorption of TMA+, which represents the cationic portion of the polymers was of lower affinity. Na+-bentonite adsorbed almost twice the amount of polycation required to fulfill the cation-exchange capacity (CEC) of the bentonite. The electrophoretic and particle size data indicated significant differences in the size of the polycation/clay flocs and the amount of polymer adsorbed on the external faces of the flocs in the presence of Na+- and Cs+-exchange ions. Correlation of this data with the NMR results suggests that the Na+-bentonite/polycation flocs are large, of low density, and that the polycation is concentrated in the interior while the Na+-ions occupy exchange sites on the external faces.