Adsorption-desorption of trichlorophenol in water-soil systems

Adsorption-desorption of trichlorophenol (TCP) on calcium montmorillonite (pure clay), prepared montmorillonite-humic complexes. and natural soils were investigated. Adsorption followed a Freundlich-type isotherm between 5 and 30 mg/L of TCP, and linear adsorption isotherms were obtained for equilibrium concentrations up to 7 mg/L. Linear correlations were obtained between sorption constants (K-p) and organic carbon (f(oc)) and clay-mineral content (f(m)). In the montmorillonite and montmorillonite-humic complex systems, adsorption and desorption isotherms coincided and no hysteresis was observed. Strong hysteresis was observed in adsorption-desorption in natural soils. The different behavior in adsorption-desorption was explained by the different nature of organic matter, its different structure, and interaction with the mineral fraction. Because trichlorophenol is a weak acid, adsorption highly depended on pH and could be predicted by combining the adsorption constant of undissociated TCP and the dissociation constant of phenol-phenolate.