Adsorption of Amphoteric Modified Bentonites to Phenol and Its Thermodynamics
两性修饰膨润土对苯酚的吸附及热力学特征

After characterizing the structure of amphoteric bentonite by X-ray diffraction and the organic carbon contents,which modified with amphoteric surfactants octadecyldimethylbetaine(BS-18),the adsorption of phenol on amphoteric bentonite and its affecting factors,i.e.modified ratio,temperature,ionic strength and pH,were studied,and the adsorption mechanism was also discussed according to its adsorption isotherms and thermodynamics.Results showed that the interlamellar spacing of amphoteric-bentonite shows a positive correlation with BS-18 modified ratio.The phenol adsorption is in sequence 150BS(150%BS-18)>100BS(100%BS-18)>50BS(50%BS-18)>25BS(25%BS-18)>CK(Unmodified soil) at 20℃ and 40℃,indicated that the phenol adsorption on bentonite can be enhanced significantly by BS-18 modification.The adsorption of phenol decreases with an increase of temperature and pH,but increases with ionic strength rise.The adsorption isotherms can be described with Henry equation.The adsorption of phenol on the amphoteric bentonite depends mainly on partition effect,because that its adsorption coefficients show a positive correlation with the organic carbon contents of amphoteric bentonite.The adsorption thermodynamics demonstrated that the phenol adsorption on amphoteric-bentonite is a physical adsorption.With the modified ratio of BS-18 increases,the phenol adsorption is a spontaneous process with characteristics of both enthalpy decrease and entropy increase in the region of 0-100% CEC ratio,while an opposite change,i.e.enthalpy increase and entropy decrease,appears when the modified ratio of BS-18 is higher than 100% CEC.