Modelling SO2−4 surface complexation on variable charge minerals: I. H+ and SO2−4 exchange under different solution conditions

Berlin

1997

S. 483-491

4 Abb., 5 Tab., 47 Lit. Ang.

Artikel aus einer ZeitschriftUnselbständiges Werk

200150034

Surface complexation of SO2−4 and H+ exchange were compared between goethite, gibbsite and a soil material from a podzol B horizon. Intrinsic equilibrium constants were determined for the surface complexation of SO2−4 and H+ using the diffuse layer model (DLM). Three surface group configurations for the SO2−4 adsorption were tested. A model with only one SO2−4 surface species and no H+ explicitly taking part in the reaction gave the overall best prediction of adsorption. The concomitant H+ exchange occurring during SO2−4 adsorption was attributed to decreased surface potential caused by charge neutralization in the inner layer. The H+/SO2−4 stoichiometric ratios (η) were determined by back-titration under different pH, ionic strength (I) and SO2−4 concentrations. The experimentally determined η was close to 1 for all materials at I= 0·1 M but 1·5, 1·0 and 1·7 in I = 1 mM for goethite, gibbsite and the soil suspension, respectively. The DLM gave a quantitatively correct description of SO2−4 and H+exchange at small I, but predictions were less accurate at large I. The surface complexation model give insight in the role of SO2−4 adsorption for the reversibility of soil acidification but remain to be evaluated in experiments more closely related to field conditions.