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The Effect of Saturating Cations on the Adsorption of Dasanit®, O,O-diethyl O-[p-(methyl sulfinyl) phenyl] phosphorothioate, by Montmorillonite Suspensions¹

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.

¹ Contribution no. 525, Research Institute, Canada Dep. of Agr., University Sub Post Office, London, Ontario N6A 3KO.

² Research Scientist, Research Institute, Canada Department of Agriculture, London, Ontario.

Received for publication August 25, 1972. Accepted for publication December 5, 1972.