substances and simple weak organic acids (3). The results
The adsorption of lactate, oxalate, malonate, phthalate, and suggest that by studying well-defined weak organic acids a citrate has been determined experimentally as a function of conbetter understanding of the interactions of ill-defined organic centration, pH, and ionic strength. The data have been described acids with mineral surfaces can be gained. with the CD-MUSIC model of Hiemstra and Van Riemsdijk [J. The knowledge obtained may also be of importance in Colloid Interface Sci. 179, 488-508 (1996)] which allows a distriunderstanding the effects of organic acid binding on the bution of charge of the organic molecule over the surface and dissolution kinetics of metal (hydr)oxides and the change in the Stern layer. Simultaneously, the concentration, pH, and salt geochemical processes, colloidal stability, and the sorption dependency as well as the basic charging behavior of goethite characteristics of silicate, iron, and aluminum oxide surfaces could be described well. On the basis of model calculations, a distinction is made between inner and outer sphere complexation (12-14).
of weak organic acids by goethite. The results indicate that the
This study focuses on the binding of well-defined weak affinity of the organic acids is dominated by the electrostatic atorganic acids by goethite. Detailed molecular information traction. The intrinsic affinity constants for the exchange reaction about the adsorption mechanisms of weak organic acids has of surface water groups and organic acids, expressed per bond, become available from conventional infrared spectroscopy increases with increasing number of reactive groups on the organic (IR) (1, 15, 16) and recently from in situ Fourier transform molecule. Ion pair formation between noncoordinated carboxylic infrared spectroscopy (in situ FTIR) studies (17)(18)(19). groups of adsorbed organic acids and cations of the background Ions can be bound by mineral surfaces by different mechaelectrolyte proved to be important for the salt dependency. The nisms. Often a distinction is made between so-called inner knowledge obtained may contribute to the interpretation of the sphere complexes (the ligand is coordinated to the metal binding of larger organic acids like fulvic and humic acids. แญง 1997 atom of the surface) and outer sphere complexes (the ligands Academic Press