MODELISATION DU COMPORTEMENT DE LA MON PAR UN « CHIMIO-TYPE » MODELLING OF NOM'S PROPERTIES BY A "CHIMIO-TYPE"

mots-cles : MON, metaux traces, proton, DPASV, PROSECE Resume : L'analyse du comportement d'acides fulviques et humiques standards (Suwannee River et Laurentian River), vis-a-vis des metaux traces (Cd, Pb) et du proton, a ete realisee a partir de differentes titrations potentiometriques et voltammetriques, par additions de solutions standards en mode logarithmique. Les donnees experimentales ainsi obtenues ont ete traitees a l'aide du logiciel PROSECE, en definissant un modele base sur un « chimio-type » constitue de proprietes discretes analysables des MON etudiees. Ce « chimio-type », constitue d'un set de trois types de « quasi-particules » (Sposito, 1981), a permis de modeliser les sites acides (6 « quasi-particules » de type I), les sites complexants echangeables (4 de type II) ainsi que les sites complexants specifiques (2 de type III) presents sur la MON. Les parametres de complexation optimises (i.e. concentrations, constantes de complexation et d'acidite de ces « quasi-particules ») permettent de prevoir le comportement de la MON vis-a-vis des metaux traces, et les phenomenes de competition metal/metal et metal/proton. Ces parametres, quasi-thermodynamiques, sont facilement integrables dans un modele de transport de contaminants tels que le modele SiAM3D-MOCO (IFREMER). Abstract: To analyse the properties of humic and fulvic acid standards (Suwannee River and Lauretian River) concerning their relation towards trace metals (Cd, Pb) and protons, several potentiometric and voltametric titrations have been carried out. The experimental results were achieved by logarithmic addition of standard solutions prior to mathematical treatment by new calculation software that was developed in our laboratory. PROSECE (Programme d'Optimisation et de SpEciation Chimique dans l'Environnement) defines a discreet model based on a so-called "chimio-type", representing the characteristics of the analysed natural organic matter (NOM). This "chimio-type" consists of three different types of "quasi-particles" (Sposito, 1981), which allows to model the acid sites (6 "quasi-particles" of type I), convertible complexing sites (4 of type II) and specific complexing sites (2 of type III) inside the NOM. Optimised complexing parameters (e.g. concentration, complexation-and acid-constants of these "quasi-particles") allow predicting the properties of NOM related to trace metals and to the phenomenon of metal/metal and metal/proton competition. These "quasi-dynamic' parameters can be integrated easily in a contaminants transport model like SiAM3D-MOCO (IFREMER).