engleski

Sorption and fractionation of natural organic matter on kaolinite and goethite

High pressure size exclusion chromatography (HPSEC) was used to determine directly the molecular-weight fractionation that occurred upon sorption of the muck fluvic acid (FA) to kaolinite and goethite, at pH 3.7, 22°C, 24 hrs. equilibration. FA sorption affinity was found to be much greater for goethite than for kaolinite, with sorption maxima, Amax=0.22 and 0.05 mgCm-2, respectively. Fractionation measurements agreeed well with theoretical predictions. at concentrations <Amax, for both sorbents, the average molecular weight (Mw) of FA remaining in solution decreased by a s much as several hundred daltons, indicating preferential sorption of the higher molecular weight components. At concentrations >Amax, solution Mw did not change, most probably because preferential sorption was overwheled by excess FA. Polydispersity decreased slighty upon sorption to kaolinite, but there was no significant change for goethite. Our results demonstrate quantitatively the preferential sorption of higher molecular weight components, and show that effects on solution Mw vary as a function of (FA).

sorption; fractionation; natural organic matter; chromatography; kaolinite; goethite

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