where the complexed solutes represented in Eq. [1] are cat-Simultaneous solution of the Gibbs-Lewis thermodynamic ions, M m , anions, A a , nonionics, U 0 , protons, H / , and hyequations for equilibrium proton and cation complexation at the droxide ions, OH 0 .
solution-metal oxide interface results in a single cation adsorption
Beginning about 1972, published cation adsorption equaequation in closed mathematical form. The simple form of the tions for the surface complex have been derived from the cation adsorption equation allows direct assessment of cation adequations of mass action for the cation alone (6-21). These sorption dependence on: (1) solution pH, (2) protonation differcation adsorption equations shared a common problem: lack ences of metal oxide surfaces, (3) differences in adsorption affinity of explicit pH dependence. Since it was well recognized that for different cations, (4) concentration of solid versus cations in cation adsorption at the solution-metal oxide interface is pH the dispersion, etc. Experimental and calculated cation adsorption results are compared. From a knowledge of the cation adsorption dependent, each publication found various means of forcing behavior combined with electrostatic potential equations, the elecexplicit pH dependence into their respective cation adsorptrostatic behavior in an interfacial system can also be determined. tion equations.
The resulting solution and interfacial electrostatic potential equa-
In just the past year, two publications (22, 23) have shown tions are single equations in closed mathematical form expressed that explicit pH dependence will arise naturally when the as explicit functions of solution and interfacial variables. The decation adsorption equation is derived by simultaneous solupendence of these variables on solution and interfacial electrostatic tion of the Gibbs-Lewis thermodynamic equations of mass potential is also examined.