Equilibrium Models in Seawater: Applications and Limitations

摘要

A knowledge of chemical species is fundamental to understanding the behavior of substances in environmental processes. Thermodynamic data provide a basis for predicting the equilibrium in environmental processes. Thermodynamic data provide a basis for predicting the equilibrium state of a chemical system. An equilibrium model for the trace constituents in seawater is illustrated using an ion-pair model for the major ions and considering copper, iron(III, cadmium, and lead as examples of trace elements. Equilibrium models have been particularly successful in accounting for the chemical behavior of many aspects of trace-metal complexation. Caution must be used in applying this approach to redox reactions and heterogeneous phase reactions because kinetic factors often limit the attainment of equilibrium. Substantial advances have been made in recent years in obtaining a suitable base of thermodynamic data for marine systems, but limitations exist because data are lacking for many trace-element reactions involving some of the important oxyanions in seawater. The existing equilibrium data base is inadequate to predict the effects of temperature and pressure on most reactions in the marine environment. (Reprints)