INFLUENCE OF TIME, PH, TEMPERATURE, ORGANIC-MATTER, EXCHANGEABLE CATION AND IONIC-STRENGTH ON THE ADSORPTION OF BENALATE ON MONTMORILLONITES

Adsorption of benalate has been examined in dilute aqueous suspensions of montmorillonite saturated with transition metal ions under variabl e conditions of time, pH, organic matter, temperature and solution ion ic strength. Maximum adsorption of the pesticide occurred at pH 6.5. T he adsorption isotherms were of S-type. The adsorption varied directly as the effective ionic radii of the exchangeable cation and inversely as the temperature, organic matter and ionic strength (upto 0.45), af ter which it became constant. The thermodynamic parameters indicated t he process to be exothermic and the adsorption of pesticides on montmo rillonite gave rise to an entropy loss. Various studies, viz. thermody namic parameters and Freundlich adsorption isotherms revealed the exis tence of protonation and/or coordination between exchangeable cation o f clay and oxygen of C=O group of benalate. However, desorption studie s showed the presence of physical adsorption.