Adsorption of alkali metal cations and halide anions on metal oxides: prediction of Hofmeister series using 1-pK triple layer model

Adsorption of electrolyte ions on metal oxides significantly affects the interfacial charge distribution. The general procedure for the prediction of surface charge on oxides in salt solutions was given by Sverjensky for the 2-pK Triple Layer Model (2-pK TLM) (Sverjensky, Geochim. Cosmochim. Acta 69:225-257, 2005). Based on his parameters values and by assuming parameters transferability (Piasecki, J. Colloid Interface Sci. 302:389-395, 2006) we have predicted the adsorption constants for three monovalent ions (Rb(+), F(-), Br(-)) for eight oxides within the framework of the 1-pK Triple Layer Model (1-pK TLM). The obtained parameters values along with the previously reported ones (Piasecki, J. Colloid Interface Sci. 302:389-395, 2006) allowed us to compare the adsorption affinities of alkali metal cations and halide anions, and construct the following Hofmeister series for the cations (Cs(+)a parts per thousand Rb(+)a parts per thousand K(+)< Na(+)< Li(+)) and for the anions (F(-)a parts per thousand << Cl(-)a parts per thousand Br(-)< I(-)) for investigated oxides. The same lyotropic series was predicted by the 2-pK TLM. It indicates that Hofmeister series is invariable during parameter transfer between surface complexation models.