Cation binding predictions of surface complexation models: Effects of pH, ionic strength, cation loading, surface complex, and model fit

Surface complexation models (SCMs) are commonly used to replicate observed acid/base and ion binding behaviors of mineral surfaces. A variety of models have been employed; the constructs can differ in representation of both the surface and the interfacial region. Little effort has been made to assess how or why model response depends on the model employed or the surface complexes considered. We have examined three SCMs and determined how model-predicted cation partitioning and proton release depend on pH, ionic strength, cation loading, model, model fit, and proposed surface complex. Significant differences were observed, between models, for comparable complexes. On the other hand, triple-layer model responses for several different complexes were almost identical over certain ranges. Model properties that contribute to the observed behaviors were considered. (C) 1997 Academic Press.