SDS对两性修饰膨润土吸附Cd2+的影响

采用十二烷基磺酸钠(SDS)复配修饰十二烷基二甲基甜菜碱(BS-12)修饰的两性修饰膨润土,以批处理法研究了不同修饰比例、温度、pH和离子强度下,SDS对两性修饰膨润土吸附Cd2+的影响,并从吸附等温线、温度效应和热力学角度探讨了吸附机制.结果表明,SDS复配修饰显著增强了两性修饰膨润土对Cd2+的吸附能力,修饰土对Cd2+的吸附量呈现BS+150SDS(BS-12+150%SDS)>BS+100SDS(BS-12+100%SDS)>BS+50SDS(BS-12+50%SDS)>BS+25SDS(BS-12+25%SDS)>BS(BS-12)>CK(原土)的顺序.修饰土对Cd2+的吸附等温线符合Langmuir模型.SDS复配修饰后,温度效应由CK和BS两性修饰土的增温正效应逐渐向BS+150SDS两性复配修饰土的增温负效应转变.pH对修饰土吸附Cd2+影响不大.离子强度增加,修饰土对Cd2+的吸附能力下降,但SDS修饰比例增加可以减弱离子强度对修饰土吸附Cd2+的影响.热力学参数结果表明,修饰土对Cd2+吸附是熵增控制的自发性过程,当SDS复配修饰比例<100%CEC时,修饰土对Cd2+吸附为焓增、熵增过程;当SDS复配修饰比例≥100%CEC时,修饰土对Cd2+吸附为焓减、熵增过程.

Effect of SDS on the Adsorption of Cd2+ onto Amphoteric Modified Bentonites

Under different modified ratios, temperatures, pH and ionic strengths, the effect of sodium dodecyl sulfonate (SDS) on the adsorption of Cd²⁺ onto bentonites which modified with amphoteric modifier dodecyl dimethyl betaine (BS-12) was studied by batch experiments, and the adsorption mechanism was also discussed. Results showed that the adsorption of Cd²⁺ on amphoteric bentonites can be enhanced significantly by SDS combined modification, Cd²⁺ adsorption decreases in the order: BS+150SDS(BS-12+150%SDS)>BS+100SDS(BS-12+100%SDS)>BS+50SDS(BS-12+50%SDS)>BS+25SDS(BS-12+25%SDS)>BS(BS-12)>CK(unmodified soil). The adsorption isotherm can be described by the Langmuir equation. The change of temperature effect from positive on CK and amphoteric bentonites to negative on BS+150SDS bentonites is observed with an increase of SDS modified ratio. The pH has little influence on Cd²⁺ adsorption on bentonites. The adsorption of Cd²⁺ on bentonites decreases with ionic strength rise, but the effect of ionic strength can be reduced with an increase of SDS modified ratio also. The adsorption thermodynamic parameters demonstrated that the adsorption of Cd²⁺ on modified bentonites was spontaneously controlled by entropy increment. When the SDS modified ratio is lower than 100% CEC, the adsorption of Cd²⁺ on modified bentonites is a process with characteristics of both enthalpy increment and entropy increment, while the SDS modified ratio is equal to or higher than 100% CEC, the adsorption of Cd²⁺ on modified bentonites becomes a process of enthalpy decrement and entropy increment.