固液相离子吸附体系中吸附剂浓度效应与Langmuir方程的适用性

ADSORBENT EFFECT AND APPLICABILITY OF LANGMUIR EQUATION FOR DESCRIBING ION ADSORPTION IN LIQUID/SOLID SYSTEMS

以蛭石吸附Zn2+和Cd2+为例,探讨Langmuir方程在固液相离子吸附体系中的适用性,结果表明:传统吸附等温线随吸附剂浓度W0增大而下降,吸附量qe不仅仅由液相平衡浓度Ce所决定,而是Ce和W0两个变量的函数;以Langmuir方程的线性形式对实验数据进行拟合,在给定吸附剂浓度水平下的实验数据与Langmuir方程拟合的相关性很好,但方程中的两个参数随吸附剂浓度增大而降低而且差异显著,表明Lang-muir方程仅适用于给定吸附剂浓度的体系,采用单一参数的Langmuir方程难以准确描述试验检测范围内Zn2+和Cd2+的吸附规律.

Experiments of Zn^2＋ and Cd^2＋ adsorptions on vermicuhte were conducted to test the applicability of Langmuir equation for describing ion adsorption in liquid/solid systems. The results showed that the traditionally defined equilibrium adsorption isotherm decreased with increasing adsorbent concentration W0, indicating that the equilibrium ion adsorption density qo is not a single function of the equilibrium ion concentration in liquid phase Ce but a function of both Ce and W0. The Langmuir equation was found to fit the experimental data well for both Zn^2＋ and Cd^2＋ only at given adsorbent concentration levels. The defined equation parameters varied significantly with a general trend towards decrease with increasing adsorbent concentration. The present findings suggest that unless the adsorbent concentration is kept constant, a single Langmuir-type equation can not be applied to describe Zn^2＋ and Cd^2＋ adsorption in the liquid/solid system.