The interaction between Roundup (glyphosate) and montmorillonite. Part I. Infrared study of the sorption of glyphosate by montmorillonite

Abstract--The adsorption mechanism of iso-propyiammonium (PAH*), the cationic omponent ofRoundup, by various homoionic montmorillonites and the structures ofthe associations obtained in the interlayer space were investigated, using infrared, X-ray, and carbon analysis methods. Adsorption from aqueous and ethanol solutions of Roundup was studied. The infrared spectra were compared with those obtained by the treatment of montmorillonites with ethanol and CCI~ solutions of the free iso-propylamine (PA). The adsorption of PA from ethanol gives rise to protonation ofthe amine. PA sorbed from CC14 solution forms an ammonium-amine association. Adsorption ofPAH + from alcohol solution of Roundup occurs by the mechanism ofcation exchange. With transition metal exchangeable cations, PAH + is sorbed in excess, forming hydrogen bonds between NH3 + groups and hydroxyls resulting from dissociation ofwater molecules. The process of adsorption ofPAH + from aqueous solutions of Roundup depends on the concentration ftbe solution. If montmorillonite is reacted with 0.5 % solution of Roundup, PAH + is adsorbed by exchanging metal cations and the adsorption capacity of the clay does not exceed the c.e.c. If the montmorillonite s reacted with 5.0 % solution of Roundup, the PAH + exchanges protons originating from the hydrolysis of the interlayer water. Protons which are transferred from the interlayer space to the water solution are accepted by the anion component ofRoundup. The amounts ofPAH + adsorbed from concentrated Roundup solutions are much higher than the cation exchange capacity of montmoriUonite. Hydrogen bonds are formed between the ammonium and water or hydroxyl groups on the interlayer space. With the trivalent exchange ions AI and Fe, which tend to polymerize inthe interlayer space, excess orption gives rise to hydrogen bonding of NH3 + to oxygen of the polymer