The incorporation of natural organic matter — cation interaction into the speciation code PHREEQE

Abstract

There is a growing need to consider the influence of organic macromolecules on the speciation of ions in natural waters. It is recognised that a simple discrete ligand approach to binding of protons/cations to organic macromolecules is not appropriate to represent heterogeneities of binding site distributions. A more realistic approach has been incorporated into the speciation code PHREEQE. Because of the concept of the speciation code the discrete ligand approach was retained but the binding intensities are modified using an electrostatic (surface complexation) model assuming the organic molecules form rigid, impenetrable spheres. The theoretical concept is discussed and the relevant changes to PHREEQE are outlined. Examples where the model is tested against literature data are shown and practical problems are discussed.