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 obse rved acid/base and ion binding behaviors of mineral surfaces. A variet y of models have been employed; the constructs can differ in represent ation of both the surface and the interfacial region. Little effort ha s been made to assess how or why model response depends on the model e mployed or the surface complexes considered. We have examined three SC Ms and determined how model-predicted cation partitioning and proton r elease 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-la yer model responses for several different complexes were almost identi cal over certain ranges. Model properties that contribute to the obser ved behaviors were considered. (C) 1997 Academic Press.