一个与吸附剂浓度有关的Langmuir等温式(英文)

A Sorbent Concentration-Dependent Langmuir Isotherm

实验测定了不同吸附剂浓度下,高岭土对Pb(Ⅱ)和Cu(Ⅱ)的吸附作用,结果表明存在明显的吸附剂浓度效应,即吸附等温线随吸附剂浓度升高而降低.采用传统的Langmuir吸附等温式对实验数据进行拟合表明,此等温式可准确地描述给定吸附剂浓度下的吸附结果,但不能预测其吸附剂浓度效应.根据表面组分活度(SCA)模型,假设吸附剂颗粒间存在相互作用,吸附剂表面吸附位的活度系数不等于1,而应为吸附剂浓度的函数,推导出了一个与吸附剂浓度有关的Langmuir(Langmuir-SCA)方程.运用高岭土吸附Pb(Ⅱ)和Cu(Ⅱ)以及文献中蛭石吸附Zn(Ⅱ)和Cd(Ⅱ)、咖啡吸附Pb(Ⅱ)的实验数据检验方程的适用性,结果表明Langmuir-SCA方程可准确地描述所观察到的吸附剂浓度效应.方程的两个内禀参数,热力学平衡常数(Keq)和特征饱和吸附量(Γ0m),与吸附剂浓度无关,并可由吸附实验数据拟合求得.

Batch adsorption experiments of Pb（Ⅱ）and Cu（Ⅱ） on kaolinite as a function of kaolinite concentration were conducted. An obvious sorbent concentration effect （Cs-effect） was observed; namely, the adsorption isotherm declines as sorbent concentration （Cs） increases. The experimental data were fitted to the classic Langmuir model. The results showed that the classic Langmuir model could adequately describe the adsorption equilibria of Pb（Ⅱ） and Cu（Ⅱ） on kaolinite for a given Cs value, but could not adequately predict the Cs-effect observed in the adsorption systems. We proposed a surface component activity （SCA） model. It suggests that the interactions between the sorbent particles exist in the real adsorption system, and the activity coefficient of the adsorption sites of the sorbent surface is a function of Cs. Based on the SCA model, a Cs-dependent Langmuir （Langmuir-SCA） isotherm was derived. The applicability of the Langmuir-SCA isotherm was examined with the experimental adsorption data of Pb（Ⅱ） and Cu（Ⅱ） on kaolinite, as well as Cd（Ⅱ） and Zn（Ⅱ） on vermiculite and Pb（Ⅱ） on coffee reported in the literature. The results showed that the Langmuir-SCA equation could describe the C3-effect observed in adsorption experiments. The two intrinsic parameters of the Langmuir-SCA isotherm, the thermodynamicequilibrium constant （Keq） and the characteristic saturation adsorption capacity （Г^0_m）, are independent of Cs and can be simulated with experimental adsorption data.