A non-equilibrium approach to modeling metal speciation in acid,aquatic systems: theory and process equations

A general algorithm (NONEQUI) was developed to simulate reversible sorption and ion exchange kinetics among a variety of heavy metals and substrates in acid (pH < 6.5) lake or stream environments. Competitive metal-substrate and substrate-substrate interactions are modeled as kinetic processes rather than invoking an instantaneous equilibrium assumption. This distinction from other models offers certain advantages when attempting to predict the fate, speciation, transport and ultimately biological effects of toxic metals in dynamic media such as lakes and streams.