BS-12+DTAB复配修饰膨润土吸附Cr(Ⅵ)和Cd2+的研究

为了探究和比较两性+阳离子复配修饰膨润土对不同类型重金属离子Cr(Ⅵ)和Cd~(2+)]的吸附效应及影响机制,采用阳离子型表面修饰剂十二烷基三甲基溴化铵(DTAB或DT)复配修饰两性表面修饰剂十二烷基二甲基甜菜碱(BS-12或BS)修饰膨润土,批处理法研究各复配修饰土样对Cr(Ⅵ)和Cd~(2+)的等温吸附的异同,并对比温度、pH值和离子强度对吸附的影响。结果表明:各复配修饰膨润土对Cr(Ⅵ)和Cd~(2+)的吸附等温线均符合Langmuir模型。供试土样对Cr(Ⅵ)的平衡吸附量呈现BS+150DT(150%CEC的DTAB复配修饰膨润土)BS+100DTBS+50DTBS+25DTBSCK(膨润土)的趋势,且最大吸附量(qm)为205.67 mmol·kg-1(BS+150DT)。土样对Cd~(2+)的平衡吸附量表现为BSCKBS+25DTBS+50DTBS+100DTBS+150DT,其qm值为232.38 mmol·kg-1(100BS)。10~40℃范围内,CK、BS修饰土对Cr(Ⅵ)吸附量为增温正效应,而BS+DT复配修饰土对Cr(Ⅵ)吸附呈现自发、焓减和熵增的特征;各供试土样对Cd~(2+)的吸附均表现为自发、焓增和熵增的特征。随着pH值的升高,各修饰土样对Cr(Ⅵ)的吸附量均逐渐降低,而对Cd~(2+)的吸附量逐渐增加。离子强度增加不利于供试土样对Cr(Ⅵ)和Cd~(2+)的吸附。BS+DT复配修饰膨润土表面的电荷类型、电荷数量是决定Cr(Ⅵ)和Cd~(2+)吸附差异的主要因素。

Studies on Cr(Ⅵ)and Cd2+adsorption onto bentonite modified by a BS-12+DTAB complex

In order to compare the discrepancies between Cr(Ⅵ)and Cd2+ adsorption on bentonite modified by a mixture of amphoteric modifier, dodecyldimethyl betaine(BS-12), and cationic modifier, Dodecyltrimethyl ammonium Bromide(DTAB), batch method was used to study the influence of temperature, ionic strength, pH on discrepancies of adsorption of Cr(Ⅵ)and Cd2+on different modified bentonites, and the thermodynamic properties were studied also. The results showed that:The Langmuir model was suited for adsorption isotherms of Cr (Ⅵ)and Cd2+on different samples. The equilibrium adsorption capacity of Cr(Ⅵ)was ordered by BS+150DT(BS-12+150％CEC DTAB)>BS+100DT>BS+50DT>BS+25DT>BS>CK(unmodified bentonite)and BS+150DT treatment had the maximum adsorption capacity(qm) 205.67 mmol·kg-1. On the contrary, the sequence of equilibrium adsorption capacity of Cd2+was BS>CK>BS+25DT>BS+50DT>BS+100DT>BS+150DT, and 100BS(100％CEC BS-12)had maximum Cd2+adsorption 232.38 mmol·kg-1. In the range of 10℃to 40℃, the adsorption capacity of Cr(Ⅵ)on CK and BS modified bentonites were increased with increased temperature, while Cr(Ⅵ)adsorption on BS-DT ben-tonites was a spontaneous process with a decrease in enthalpy and an increase in entropy. The Cd2+adsorption on different samples was a spontaneous process with an increase in enthalpy and an increase in entropy. With an increase of pH, the adsorption capacity of Cr(Ⅵ)de-creased gradually, while the adsorption capacity of Cd2+increased gradually. High ionic strength was not conducive to adsorption of Cr(Ⅵ) and Cd2+. Charge type of BS-DT complex modified bentonite was the crucial factor to difference between Cr(Ⅵ)and Cd2+adsorption.