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

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Langmuir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.

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

Experiments of Zn2 and Cd2 adsorptions on vermiculite 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 qe 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 Zn2 and Cd2 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 Zn2 and Cd2 adsorption in the liquid/solid system.