两性修饰膨润土对苯酚的吸附及热力学特征

采用两性修饰剂十八烷基二甲基甜菜碱(BS-18)制备两性修饰膨润土,通过X射线衍射和有机碳质量分数分析表征了修饰土的结构;以批处理法研究了两性修饰膨润土对苯酚的吸附规律,考察了修饰比例、温度、pH和离子强度这4个因素对吸附的影响,并从吸附等温线和吸附热力学角度分析探讨了其吸附机制.结果表明,两性修饰土的底面层间距与修饰比例呈正相关;两性修饰后的土样对苯酚的吸附能力显著增强,20℃和40℃时均表现为150BS(150%BS-18)>100BS(100%BS-18)>50BS(50%BS-18)>25BS(25%BS-18)>CK;吸附量随温度、pH的增加而减小,随离子强度的增大而增大;Henry模型适用于描述苯酚的吸附;苯酚在供试土样上的吸附以分配作用为主,分配系数与有机碳质量分数呈正相关;BS-18修饰土样吸附苯酚是一个自发的物理吸附过程,在0～100%CEC比例时,随修饰比例的增大,吸附呈现焓减、熵增特征,而100%～150%CEC阶段,吸附则表现出相反的特征.

Adsorption of Amphoteric Modified Bentonites to Phenol and Its Thermodynamics

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.