Single Cation Adsorption Equation for the Solution-Metal Oxide Interface.

Simultaneous solution of the Gibbs-Lewis thermodynamic equations for equilibrium proton and cation complexation at the solution-metal oxide interface results in a single cation adsorption equation in closed mathematical form. The simple form of the cation adsorption equation allows direct assessment of cation adsorption dependence on: (1) solution pH, (2) protonation differences of metal oxide surfaces, (3) differences in adsorption affinity for different cations, (4) concentration of solid versus cations in the dispersion, etc. Experimental and calculated cation adsorption results are compared. From a knowledge of the cation adsorption behavior combined with electrostatic potential equations, the electrostatic behavior in an interfacial system can also be determined. The resulting solution and interfacial electrostatic potential equations are single equations in closed mathematical form expressed as explicit functions of solution and interfacial variables. The dependence of these variables on solution and interfacial electrostatic potential is also examined.