Adsorption of Terbutryne on Metal-Montmorillonites

Adsorption of terbutryne (2-methyl thio, 4-ethyl amino, 6-tertiary butyl amine-S-triazine) on Cu, Zn, Ca, Mg and Al-montmorillonites was studied at 30 and 40°C. The adsorption conformed well to Freundlich and Langmuir adsorption isotherms. The amount of terbutryne adsorbed decreased in the order Al>Cu>Ca>Zn>Mg-montmorillonite. Equilibrium constants for adsorption were calculated from temperature studies and from this the standard enthalpy and entropy of adsorption. A wide variation in the value of equilibrium constants and standard enthalpy of adsorption point towards differences in the mode of binding of the herbicide to the metal clays. Desorption studies indicate some Irreversible fixation of terbutryne also. Some decomposition of terbutryne was also brought about by adsorption on Al and Cu-montmorillonites. This is attributed to protonation of terbutryne in Al-montmorillonite and coordination to Cu in the Cu-montmorillonite by terbutryne.