Modeling of the Association of Metal Ions with Heterogeneous Environmental Sorbents

Abstract

AbstractThe use of mechanistic (surface-complexation, electric-double layer) and semi-empirical (affinity spectrum) models for representation of the association of metal ions with heterogeneous environmental materials, such as humic acids and soil particle surfaces, is compared. It is seen that mechanistic models are not nearly as mechanistic as one generally assumes, and that semi-empirical models are much more valuable than one might assume by comparison to simple Kd, models. A semi-empirical discrete-log-K-spectrum model was used to describe the binding of Co(II), as a function of pH and NaClO4 concentration, to two environmental substrates: leonardite humic acid and a kaolinitic subsoil. Excellent agreement of the model and the data was obtained over a wide range of solution composition. These models appear to be the most promising among several alternatives for modeling interactions of metal ions with complex heterogeneous environmental materials over a wide range of solution composition.