The Sorption of Synthetic Surface-Active Compounds by Carbon Black

Abstract

The sorption on carbon black of a number of types of anionic, cationic, and nonionic surface- active compounds from aqueous solutions has been measured. It is shown that the sorption of these compounds does not conform to the Freundlich adsorption isotherm over the whole of the concentration range studied (0.01%—0.2% by weight). In the majority of cases an abrupt change in slope of the curve occurred at concentrations which appear to correspond, at least approximately, to the critical micelle concentrations of the various compounds. At con centrations above this critical point the plot of log X vs. log C appeared to be linear, but below the critical point considerable deviation from lineality was observed in some cases. The sorption of sodium alkyl sulfates increased with increasing chain length of the alkyl group at constant temperature, and decreased with increasing temperature at constant chain length. A series of compounds differing widely in chemical constitution, and including both anionic and cationic agents, were shown to be remarkably similar with respect to the general level of adsorption. Two typical nonionic compounds were found to be sorbed somewhat more strongly, particularly at higher concentrations, than any of the other compounds investigated. The addition of sodium sulfate to solutions of anionic compounds resulted in an increase in the sorption of the latter in every case.