Modeling the binding of fulvic acid by goethite: the speciation of adsorbed FA molecules

Under natural conditions, the adsorption of ions at the solid–water interface may be strongly influenced by the adsorption of organic matter. In this paper, we describe the adsorption of fulvic acid (FA) by metal(hydr)oxide surfaces with a heterogeneous surface complexation model, the ligand and cha...

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Published inGeochimica et cosmochimica acta Vol. 67; no. 8; pp. 1463 - 1474
Main Authors Filius, Jeroen D., Meeussen, Johannes C.L., Lumsdon, David G., Hiemstra, Tjisse, van Riemsdijk, Willem H.
Format Journal Article
LanguageEnglish
Published Elsevier Ltd 15.04.2003
Subjects
charge
competitive adsorption
humic substances
hydrous oxides
ion-binding
iron-oxide
natural organic-matter
nica-donnan model
proton binding
surface complexation
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Summary:Under natural conditions, the adsorption of ions at the solid–water interface may be strongly influenced by the adsorption of organic matter. In this paper, we describe the adsorption of fulvic acid (FA) by metal(hydr)oxide surfaces with a heterogeneous surface complexation model, the ligand and charge distribution (LCD) model. The model is a self-consistent combination of the nonideal competitive adsorption (NICA) equation and the CD-MUSIC model. The LCD model can describe simultaneously the concentration, pH, and salt dependency of the adsorption with a minimum of only three adjustable parameters. Furthermore, the model predicts the coadsorption of protons accurately for an extended range of conditions. Surface speciation calculations show that almost all hydroxyl groups of the adsorbed FA molecules are involved in outer sphere complexation reactions. The carboxylic groups of the adsorbed FA molecule form inner and outer sphere complexes. Furthermore, part of the carboxylate groups remain noncoordinated and deprotonated.
ISSN:0016-7037
1872-9533
DOI:10.1016/S0016-7037(02)01042-6