硅酸镁锂的有机改性及对Cr(Ⅵ)的吸附特性

摘要

采用水热法合成了硅酸镁锂(Laponite),然后利用十六烷基三甲基溴化铵(CTMAB)对其进行有机改性,研究了改性后的有机硅酸镁锂(CTMABL)对Cr(Ⅵ)的吸附特性.结果表明,改性后样品的比表面积和孔容积变小而平均孔径增大.CTMABL样品的d(001)值从改性前的1.23 nm增加到1.79 nm,表明CTMAB进入Laponite层间.随着溶液pH值的提高,CTMABL对Cr(Ⅵ)的吸附效率明显下降;pH<8.5时,CTMABL颗粒表面电势为正,能够与Cr(Ⅵ)阴离子发生静电吸引从而提高吸附效率.随着固液比增加,对Cr(Ⅵ)的去除效率迅速上升,当固液比达到4 g/L后去除效率趋于稳定.离子强度对Cr(Ⅵ)吸附过程的影响不明显.CTMABL对Cr(Ⅵ)的吸附符合准二级动力学模型,吸附传质速率受膜扩散和颗粒内扩散过程共同影响.等温吸附过程符合Langmuir模型,热力学分析结果表明吸附过程是一个自发的吸热反应.综合分析认为表面配合作用是主要的吸附机制,同时静电引力在吸附过程中起到了促进作用.%Laponite was synthesized by hydrothermal method and modified by cetyltrimethyl ammonium bro-mide(CTMAB). The adsorption of Cr(Ⅵ) on modified laponite(CTMABL) as a function of pH, CTMABL dosage, ionic strength, contact time, and temperature was studied via batch technique. The results showed that the specific surface area and pore volume of modified samples were decreased, while the average pore size was increased. The d(001) value of CTMABL raised from 1. 23 nm to 1. 79 nm after the modification, which in-dicated that the CTMAB had entered into the interlayer of laponite. The removal of Cr(Ⅵ) from solution in-creased with the increase of solution pH value. At pH<8. 5, the surface Zeta potential of CTMABL particles is positive, and thus the adsorption efficiency can be promoted by the electrostatic attraction between CTMABL particles and Cr(Ⅵ) anions. The adsorption of Cr(Ⅵ) on CTMABL increased with the increase of adsorbent dosage, maintaining a removal efficiency of >99% at the dosage of 4 g/L. The effect of ionic strength on the adsorption of Cr(Ⅵ) was not obvious. The adsorption kinetic data of Cr(Ⅵ) on CTMABL were well described by the pseudo-second-order kinetics model, and the adsorption rate was influenced by the membrane diffusion and intra-particle diffusion. The adsorption isotherms of Cr (Ⅵ) on CTMABL can be described well by the Langmuir model. The thermodynamic parameters of Cr(Ⅵ) adsorption on CTMABL at different temperatures indicated that the adsorption was endothermic and spontaneous. The adsorption of Cr(Ⅵ) was dominated by surface complexation, whereas electrostatic attraction could also promote the Cr(Ⅵ) adsorption on CTMABL.