Evaluation of internally consistent parameters for the triple-layer model by the systematic analysis of oxide surface titration data

Details Evaluation of internally consistent parameters for the triple-layer model by the systematic analysis of oxide surface titration data Evaluation of internally consistent parameters for the triple-layer model by the systematic analysis of oxide surface titration data

Jul 1997

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1997gecoa..61.2801s&link_type=abstract

Geochimica et Cosmochimica Acta, vol. 61, Issue 14, pp.2801-2826

Computer Science

7

Scientific paper

Systematic analysis of surface titration data from the literature has been performed for ten oxides (anatase, hematite, goethite, rutile, amorphous silica, quartz, magnetite, -MnO 2 , corundum, and -alumina) in ten electrolytes (LiNo 3 , NaNO 3 , KNO 3 , CsNO 3 , LiCl, NaCl, KCl, CsCl, NaI, and NaClO 4 ) over a wide range of ionic strengths (0.001 M-2.9 M) to establish adsorption equilibrium constants and capacitances consistent with the triple-layer model of surface complexation. Experimental data for the same mineral in different electrolytes and data for a given mineral/ electrolyte system from various investigators have been compared. In this analysis, the surface protonation constants (K,, and K s,2 ) were calculated by combining predicted values of pK ( log K s,2 - log K s,1 ) (Sverjensky and Sahai, 1996) with experimental points of zero charge; site-densities were obtained from tritium-exchange experiments reported in the literature, and the outer-layer capacitance (C 2 ) was set at 0.2 F·m -2 . This scheme permitted us to retrieve consistent sets of values for the inner layer capacitance (C 1 ), and for the electrolyte adsorption constants ( K s,L - and K s,M + ) corresponding, respectively, to the equilibria >SOH 2 + + L aq - = >SOH 2 + - L - and >SO - + M aq + = >SO - - M + Aqueous activity coefficients were calculated using the extended Debye-Huckel equation (Helgeson et al., 1981), which is valid to high ionic strengths (>0.5 M). Systematic analysis of the data reveals important trends and differences between triple-layer model predictions and experimental data and between data for the same mineral/ electrolyte from different investigators. Furthermore, the analysis yields an internally consistent set of triple-layer parameters which will be used in developing a predictive model for electrolyte adsorption based on Born solvation and electrostatic theory (Sahai and Sverjensky, 1997a).

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