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Adsorption of Pesticides onto Quartz, Calcite, Kaolinite, and -Alumina

^a Dep. of Geology and Geotechnical Engineering, Technical Univ. of Denmark, Building 204, DK-2800 Lyngby, Denmark
^b Dep. of Geochemistry, Geological Survey of Denmark and Greenland, Thoravej 8, DK-2400 Copenhagen, Denmark

View larger version (145K): [in a new window]   Fig. 1. Scanning electron micrographs (SEMs) of mineral powders. (A) quartz, (B) calcite, (C) -alumina, (D) kaolinite. The scalebar in the SEM image of the quartz powder is 20 µm, whereas the scalebar in the other images is 2 µm.

View larger version (17K): [in a new window]   Fig. 2. Structural formulae of herbicides used in sorption studies.

View larger version (31K): [in a new window]   Fig. 3. Distribution coefficients (Kd) normalized to surface area, as a function of equilibrium concentration of sorbate in solution. Error bars indicate standard deviation.

View larger version (33K): [in a new window]   Fig. 4. Freundlich adsorption isotherms shown on a log scale for the sorption of 2,4-D, atrazine, and isoproturon on minerals. The Freundlich constant (KF) is given in (µmol/m2) (µmol/mL)-n. Error bars indicate standard deviation (may be covered by the symbols).

View larger version (28K): [in a new window]   Fig. 5. Atrazine adsorption isotherms on a linear scale for the sorption on quartz and kaolinite. Full symbols denote adsorption points where the pesticide solutions were added after equilibration of the water–mineral system. Open symbols denote adsorption points where the pesticide solutions were added directly to the dried mineral powder. The Freundlich constant (KF) is given in (µmol/m2) (µmol/mL)-n. Error bars indicate standard deviation (may be covered by the symbols).

View larger version (24K): [in a new window]   Fig. 6. 2,4-D adsorption isotherms on a linear scale for the sorption on quartz, calcite, and -alumina. Full symbols denote adsorption points where the pesticide solutions were added after equilibration of the water–mineral system. Open symbols denote adsorption points where the pesticide solutions were added directly to the dried mineral powder. The Freundlich constant (KF) is given in (µmol/m2) (µmol/mL)-n. Error bars indicate standard deviation (may be covered by the symbols).

View larger version (30K): [in a new window]   Fig. 7. Effect of CaCl2 as electrolyte on the sorption of selected pesticides by quartz, calcite, -alumina, and kaolinite. The solution conditions are: temperature = 10°C, pH (quartz) = 6.7 ± 0.1, pH (calcite) = 8.8 ± 0.1, pH (-alumina) = 7.0 ± 0.1, pH (kaolinite with CaCl2) = 5.9 ± 0.1, and pH (kaolinite without CaCl2) = 6.5. Error bars indicate standard deviation.