The Effect of Saturating Cations on the Adsorption of Dasanit®, O,O‐diethyl O‐[p‐(methyl sulfinyl) phenyl] phosphorothioate, by Montmorillonite Suspensions

Abstract

A study was conducted to examine the adsorptive behavior of Dasanit in montmorillonite suspensions as affected by saturating cations and the clay suspension concentration. Adsorption isotherms, similar to Type III or Class “S” isotherms, were constructed for 10 cation‐saturated montmorillonites. Infrared spectroscopy was used to examine the relative polarities of the sulfoxide, sulfone, phosphoryl, and carbonyl groups as they occur in Dasanit, in some of its oxidation products, and in several other insecticides. Despite its polar nature, Dasanit did not appear to adsorb on the interlayer surfaces of montmorillonite. X‐ray diffraction data for dry Dasanit‐montmorillonite systems showed a maximum interlayer expansion of 2.7Å. Kinetic data showed that the adsorption process reached equilibrium in less than 15 min. The sequence of the upper linear segments of the 10 isotherms appeared to be related to valence, atomic weight, and co‐ordinating habits of the saturating cations. The Fe‐montmorillonite system adsorbed the most Dasanit. At a suspension concentration of 15 mg/ml, this system removed 99% of the Dasanit from solution. The maximum adsorption value obtained for Fe‐montmorillonite was 0.354 mg/mg clay at a suspension concentration of 0.25 mg/ml. This value corresponded to approximately 4.8 Dasanit monolayers on the exterior clay surface. Desorption studies indicated that those clays with the greatest adsorption capacity exhibited the least desorption tendency. The decreasing order of desorption was Na − > Ca − > Al − > Cu − montmorillonite.

Sorption of organophosphorus and carbamate insecticides by soil

“…Mechanisms were similar to those proposed for parathion, i.e., hydrogen bonding via water bridges between polar func tional groups and adsorbed cations (Bowman et al 1970;Bowman 1973;Singhal and Singh 1978).…”

“…Bowman (1973) found that the saturating cation on montmorillonite affected adsorption of fensulfothion in the following order of retention:…”

Surface Condensation of Organophosphate Esters on Smectites

“…A number of studies (e.g., Bowman, 1973;Bowman and Sans, 1977;Yaron and Saltzman, 1972;Gerstl and Yaron, 1978;Yaron, 1978) on the interaction of these and other organophosphate esters with various clays in aqueous and nonpolar media have shown that the adsorption of organophosphate esters on a clay surfaee is highly dependent on the exchangeable cation and its hydration state. Previous studies investigated the low part of the adsorption isotherms; yet, if clays are to be used as carriers for pesticides or other bioactive substances, it is important, for example, to study the interactions oforganophosphate esters on clays at high surface concentrations.…”

Effects of Increasing Potassium Chloride and Calcium Chloride Ionic Strength on Pesticide Sorption by Potassium‐ and Calcium‐Smectite

“…This view is exemplified by the reliance on soil organic carbon-normalized sorption coefficients (K OC ) to predict the fate and transport of organic compounds in soils. However, several recent studies and a few earlier ones provide clear evidence that soil minerals can function as effective adsorbents for pesticides and organic contaminants under environmentally relevant conditions (Bailey et al, 1968;Bowman, 1973;Boyd et al, 2001;Celis et al, 1998;Haderlein et al, 1996;Hundal et al, 2001;Johnston et al, 2002;Laird et al, 1992;Mortland, 1970;Sheng et al, 2002;Zhu et al, 2004). For important categories of pesticides (e.g., triazines, carbamates, ureas, nitrophenols, benzonitrile) and organic contaminants (e.g., nitroaromatics), sorption by clays can be equal or greater than that by SOM based on comparisons of sorption by a unit mass of isolated clay minerals vs. SOM and by synthetic clay-organic matter complexes (Li et al, 2003;Sheng et al, 2001).…”