Excess adsorption on hydrophobic and hydrophilic solid-liquid interfaces: Negative adsorption of electrolytes and urea. Part 2

Abstract

The extent of hydration of charcoal, cationic and anionic resin powders in the presence and absence of some inorganic salts and urea has been studied using isopiestic vapour pressure technique. The shapes of water vapour adsorption isotherms for different solids agree with type III BET isotherms. At water activity approaching unity, maximum values of water adsorption Delta n(1)(0) in moles per square meter of solid at 30 degrees C are in the order: cationic resin > anionic resin > charcoal. Standard free energies (Delta G degrees), of adsorption of water vapour have also been evaluated. The negative and positive excess hydration of these solid powers for different mole fractions of LiCl, NaCl, KCl, Na2SO4 and urea in the bulk phase have been estimated using data obtained from the isopiestic experiments. The free energies of excess hydration for all these systems have been evaluated using the integrated forms of the Gibbs adsorption equations. The absolute values of water and salt binding to these solids have been estimated in the bulk phase.