| Abstract
| - The aim of the present work is to model iron speciationduring its interaction with natural organic matter. Experimentaldata for iron speciation were achieved with an insolubilisedhumic acid used as an organic matter analogue for 30 μMto 1.8 mM total iron concentrations and 2 ≤ pH ≤ 5.5. IHAwas found to be able to impose its redox potential tothe solution and therefore the Fe(II)/Fe(III) ratio. Model VIand the NICA-Donnan model have been adjusted toexperimental results of acid−base titrations, total ironmeasurements, and redox speciation in solution. They bothdescribe well pH and concentration dependence of ironadsorption. For high iron concentration, Fe(III) solution activityis limited by precipitation of a poorly ordered Fe oxyhydroxidewith a higher solubility (log Ks = 5.6−5.7) than ferryhydritedescribed in the litterature.
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