BS+DT和BS+SDS复配修饰红壤对Cd2+吸附的比较

为了比较两性-阳离子和两性-阴离子复配修饰可变电荷土壤对Cd~(2+)吸附的差异,采用阳离子型表面修饰剂十二烷基三甲基溴化铵(DT)和阴离子型表面修饰剂十二烷基磺酸钠(SDS)分别对十二烷基二甲基甜菜碱(BS)两性修饰红壤进行复配修饰,以批处理法研究各供试土样的等温吸附及热力学特征,并对比了修饰比例、温度、pH和离子强度对吸附的影响。结果表明:阳、阴离子对两性修饰红壤的复配修饰具有相反的效应,BS+DT复配修饰红壤对Cd~(2+)吸附量随DT修饰比例的增加而减小,BS+SDS复配修饰红壤对Cd~(2+)的吸附量随SDS修饰比例的增加而增加。供试土样对Cd~(2+)饱和吸附量呈现出BS+SDSBSCK(红壤)BS+DT的规律,Sips模型能够较好地描述Cd~(2+)在各供试土样上的吸附机制。各供试土样对Cd~(2+)的吸附均呈现出吸热、熵增、自发的特征,低离子强度和高pH有利于Cd~(2+)的吸附。可变电荷土壤表面负电荷数量较少是造成阳、阴离子复配修饰对Cd~(2+)吸附差异的关键因素。

Comparison of Cd2+ adsorption onto BS+DT and BS+SDS in complex modified red soil

In order to compare the difference of cadmium ion(Cd²⁺)adsorption on two amphoteric complex modified red soils, amphotericcationic complex modified red soil was prepared with an amphoteric modifier dodecyldimethyl betaine(BS)and a cationic modifier dodecyldimethylammonium bromide(DT). Amphoteric-anionic complex modified red soil was also prepared with BS and anionic modifier sodium dodecyl sulfonate(SDS). The Cd²⁺ adsorption isotherm and its thermodynamic properties was conducted by batch experiments, and the influence of total modifier ratios, temperature, pH and ionic strength was investigated. The results indicated that the cationic complex modifier DT showed an opposite effect against anionic complex modifier SDS, and the Cd²⁺adsorption capacity decreased when the modifier ratio of DT was increased, while it increased with an increase in the modifier ratio of SDS. The maximum adsorption capacity of Cd²⁺ was ordered by BS+SDS > BS > CK(red soil) > BS+DT. The Sips model was the best model for describing Cd²⁺ adsorption isotherms on different modified soils. The adsorption of Cd²⁺in both BS-DT and BS-SDS modified red soil increased with an increase of both temperature and pH, but decreased with an increase of ionic strength. The adsorption of Cd²⁺ was a spontaneous process with endothermic and entropy increment characteristics. The low negative charge of variable charge soils is the key factor for deciding the difference of Cd²⁺ adsorption on amphotericcationic and amphoteric-anionic modified soil.