engleski

Adsorption of Oxalic Acid on Hematite: Application of the Surface Potential Measurements

Surface potential at hematite / oxalic acid aqueous solution interface was measured by hematite Single Crystal Electrode. Simultaneous interpretation of surface potential, electrokinetic potential and adsorption data for adsorption of oxalic acid on hematite surface was introduced. Interpretation based on the Surface Complexation Model suggested that oxalate ion is bound to metal ion at the solid surface forming the singly charged oxalate surface complex with charge exposed to the potential at the outer Helmholtz layer. The equilibrium parameters describing the interfacial equilibrium were obtained as follows. For two steps of protonation of surface sites, the thermodynamic equilibrium constants are: lg K1 = 7.1 ± ; ; ; ; 0.4 and lg K2 = 5.2 ± ; ; ; ; 0.4, respectively. Regarding the adsorption equilibrium constant two assumptions were tested ; i.e. the charge of surface complex is exposed to inner surface potential Ψ 0 or to outer surface potential Ψ d. From the required constancy of the interfacial equilibrium constants one may conclude that the latter assumption was found to be more appropriate. The obtained adsorption equilibrium constant is lg Kads = 3.0 ± ; ; ; ; 0.8. It was shown that the surface potential measurement by Single Crystal Electrodes is a helpful tool in elucidation of the complex equilibrium at the interface.

Surface potential; hematite; oxalic acid; Surface Complexation Model; Electrical Interfacial Layer

nije evidentirano