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.