Adsorption of Small Weak Organic Acids on Goethite: Modeling of Mechanisms

Interactions Between Ionic Pesticides and Model Systems for Soil Fractions

“…At pH 4 there is a strong electrostatic interaction between both substances, but the adsorption decreases linearly with increasing pH because of the decrease in the positive surface charge of the goethite, so that at pH values close to the PZC, there is little interaction between the organic anions and the surface. This response is similar to that observed by Filius et al (1997Filius et al ( , 2001, who studied the adsorption of small organic acids on goethite and attributed the decrease in www.intechopen.com adsorption at increasing pH to the fact that the sorbent-sorbate interaction is usually dominated by electrostatic effects. The present experiments involving MCPA adsorption on goethite did not show any significant adsorption of the herbicide at pH 7.0 or higher, at which the surface charge on the goethite is less positive or even negative.…”

“…Among the experimental results that correspond to the interaction between the pesticide and the surface groups of goethite, the part of the isotherm which displays Langmuir behaviour ( Figure 4b) has been interpreted with the CD-MUSIC model (Iglesias et al, 2010a). It can be assumed, as for other simple organic acids (Filius et al, 1997), that the carboxylic groups of the organic molecules can form inner-sphere and outer-sphere surface complexes with the singly coordinated surface groups (≡FeOH -0.5 ), and that the triply coordinated surface groups (≡Fe 3 O -0.5 ) do not take part in the MCPA binding ( Figure 5). In the inner-sphere complexes, one oxygen atom of the carboxylate group is exchanged for a surface water group.…”

The relationship between molecular structure and ion adsorption on variable charge minerals

“…4 to indicate the estimated conditions where the charge distribution can potentially result from charge transfer of hydrogen bridges in outer sphere complexes (Filius et al, 1998). The maximum effect of this charge distribution from changes in hydrogen bonding is estimated to be 0.2 charge units per bond in case of strong hydrogen bond formation.…”

Nanoparticles in natural systems II: The natural oxide fraction at interaction with natural organic matter and phosphate

“…and Dz 1 = À0.5 v.u. (Filius et al, 1997). Overall, the reaction will neutralize the surface oxygen charge (changing from À1/2 to 0 v.u.)…”