Corrected Debye-Huckel analysis of surface complexation I. Bulk salt limit

Statistical mechanics in the framework of generalized van der Waals theory is used to clarify the mechanisms at work in surface complexation. As a fir st step this article will focus on a description of ion interactions in sol ution. A simple semiempirical theoretical framework is proposed on the basi s of an extension of the Debye-Huckel theory of the screening mechanism. Io n size effects are accounted for within a restricted primitive model of the electrolyte leading to a shift in the Debye screening length. Remarkably t he shift is found to be due only to hole correction of the electrostatic po tential energy while the excluded volume effects vanish in the linear appro ximation. The treatment of diffuse screening is tested by application of th e corrected Debye-Huckel theory to the calculation of bulk thermodynamic pr operties, such as the internal energy, the osmotic coefficient, and mean io nic activity coefficients. Calculations and comparisons with experimental d ata have been performed for 1: 1, 2: 1, 3: 1, and 2:2 salt solutions. The a ccuracy is good indicating that the theory is suitable for the intended app lication in the study of surface complexation. Finally our theory is applie d to electrolyte solutions in the solvent primitive model where the solvent is represented by neutral hard spheres. Our analysis indicates that, withi n the limits of our basic assumptions, the solvent hard spheres only enter the background contributions and leave the screening mechanism unaffected. The simulation results available indicate that this is largely, if not enti rely, correct. (C) 2001 Academic Press.