Submitted to: Clay Minerals
Publication Type: Peer reviewed journal
Publication Acceptance Date: 9/7/2000
Publication Date: N/A
Citation: Interpretive Summary: The most widely used method to remediate contaminated sites is the removal of the organic pollutants by activated carbon; however, the increasing sorbent demand is stimulating research to look for new sorbent materials. Because of the character of their surfaces, clays are very good sorbents for certain types of organic molecules, but poor for other types of compounds. The sorptive properties of the clays however, can be significantly enhanced by replacement of natural positively-charged metals on the clay surface with large positively-charged organic molecules. In present paper, we used the pesticide imidacloprid, which is a new systemic insecticide of the chemical group nitroguanidine, as a test compound to comparatively evaluate the ability of two clays and their organoderivatives (organoclays) as potential sorbents for remediation of polar organic molecules, which are a concern because they can be highly water soluble. These clays could be used to reduce the leaching potential of imidacloprid associated with its high application rate used for termite control. These results would also provide information on imidacloprid-clay interactions, on which there are no published reports. We have determined the mechanism by which imidacloprid binds to these clays. We have also determined that varying the organic molecule on the clay can be used to increase sorption and hence, we can manipulate the potential mobility of imidacloprid associated with clays. While the results appear promising, additional research is still needed to determine if these types of organoclays would be good sorbents for remediation of contaminated soil and water.
Technical Abstract: Sorption of imidacloprid on organic saturated octadecylammonium (C18) and dioctadecyldimethylammonium (DOD) and inorganic (Fe) saturated Wyoming (SW) and Arizona (SA) montmorillonites has been investigated. Sorption isotherms were fitted to the Freundlich equation. Imidacloprid-montmorillonite complexes were studied by X-ray diffraction and FT-IR techniques. Imidacloprid sorption coefficients, Kf, decreased in the order SWC18> SAC18>SWFe>SWDOD>=SADOD. The low layer charge and saturation by primary alkylammonium cation facilitates sorption of imidacloprid in the interlayer of the smectite, corroborated by the increase in basal spacing observed in X-ray diffractograms and by the presence of absorption band shifts in FT-IR spectra. Imidacloprid sorbs in the interlayer space of smectite mainly by hydrophobic interactions with the alkylchains in organic smectites and with uncharged siloxane surface in Fe(III)-smectite. Further polar bonds between nthe NO2 group of imidacloprid and NH of the primary alkylcations and protonation of imidacloprid in Fe-smectites enhanced sorption in these cases.