双子型复配增强两性膨润土吸附Cr(VI)的效应

Enhancing effect of gemini surfactant complex modification on Cr(VI)adsorption by amphoteric bentonite

在两性修饰剂十二烷基二甲基甜菜碱(BS)修饰膨润土的基础上,采用双子型阳离子修饰剂乙撑基双十四烷基二甲基氯化铵(EB)对其进行复配修饰,以批处理法研究了不同修饰比例、温度、pH值和离子强度条件下,BS+EB复配修饰膨润土对Cr(VI)的吸附规律和热力学特征,并通过吸附Cr(VI)前后BS+EB复配修饰膨润土的红外光谱和表面电荷探讨了其吸附机制.结果表明,与BS两性修饰膨润土比较,EB复配修饰显著增强了其对Cr(VI)的吸附能力,吸附量增加了2.02~27.25倍,30℃时吸附量呈现BS+150EB(BS和150%比例的EB复配修饰膨润土)>BS+100EB>BS+50EB>BS+25EB>BS>CK(膨润土)的趋势,对Cr(VI)的吸附量随EB修饰比例增加而上升.CK、BS修饰膨润土对Cr(VI)呈现自发、熵增和焓增的特征,而BS+EB复配修饰膨润土对Cr(VI)吸附量随着温度的升高而降低,呈现出增温负效应.随着pH值的升高、离子强度增加,各供试土样对Cr(VI)的吸附量逐渐降低.红外光谱和土壤表面电荷结果证实电荷引力是BS+EB复配修饰土吸附Cr(VI)的主要机制.

A series of amphoteric-cationic complex modified bentonites were prepared with amphoteric modifier dodecyldimethyl betaine(BS)and gemini cationic surfactant ethylene ditetradecyl dimethyl ammonium chloride(EB),Cr(VI)adsorption on BS+EB complex modified bentonite under different modification ratio,temperature,pH and ionic strength and its thermodynamic characteristics were studied by batch method,its adsorption mechanism was discussed by comparing surface charge and infrared spectrum of BS+EB complex modified bentonite before and after Cr(VI)adsorption.The results showed that EB complex modification significantly enhanced its adsorption capacity for Cr(VI),which was 2.02~27.25 times higher than that on BS amphoteric modified bentonite.The Cr(VI)adsorption increased with an increase of EB modification ratio at 30℃and was ordered by BS+150EB(BS and 150%EB complex modified bentonite)>BS+100 EB>BS+50EB>BS+25EB>BS>CK(bentonite).The Cr(VI)adsorption on both CK and BS modified bentonite was a spontaneous process with a characteristics of both enthalpy-increase and entropy-increase,except it on BS+EB complex modified bentonite decreased with an increase of temperature,showing a characteristics of negative temperature effect.With an increase of pH and ionic strength,the adsorption of Cr(VI)on each sample decreased gradually.The results of infrared spectra and soil surface charge confirmed that charge attraction was the main mechanism for Cr(VI)adsorption on BS+EB complex modified bentonite.