经典等温吸附模型在重金属离子/硅藻土体系中的应用及存在问题

Application of Classical Isothermal Adsorption Models in Heavy Metal Ions/Diatomite System and Related Problems

为了深入了解天然硅藻土对常见重金属离子Cu2+、Zn2+、Pb2+、Cd2+、Mn2+、Fe3+的吸附属性,同时也为了发现经典等温吸附模型应用于液/固体系时存在的问题,开展了系列等温吸附研究.结果表明,最适于描述天然硅藻土对Pb2+、Cd2+、Cu2+、Zn2+、Mn2+、Fe3+吸附的模型分别为Tenkin、Tenkin、Langmuir、Tenkin、Freundlich和Freundlich模型.各离子在天然硅藻土上的吸附以物理过程为主,吸附反应容易进行.液/固体系中,应用经典等温吸附模型对试验数据进行线性拟合时,发现平衡吸附量q e不是离子平衡浓度c e的唯一函数,而是c e与吸附剂浓度W0两个变量的函数,q e与c e/W0具有一一对应的函数关系.经典等温吸附模型存在明显的吸附剂浓度效应,参数值不稳定,模拟值与实测值差异显著,缺乏实际指导意义.试验证明新的四组分模型可用于描述天然硅藻土-水溶液体系中单一离子的吸附行为,新模型参数k与q m值也具有唯一性,可用于给定体系的实际定量计算.

In order to fully understand adsorption nature of Cu2 ＋ , Zn2 ＋ , Pb2 ＋ , Cd2 ＋ , Mn2 ＋ , Fe3＋ onto natural diatomite, and to find problems of classical isothermal adsorption models＇ application in liquid/solid system, a series of isothermal adsorption tests were conducted. As results indicate, the most suitable isotherm models for describing adsorption of Pb2 ＋ , Cd2. , Cu2 ＋ , Zn2 ＋ , Mn2 ＋ , Fe3 ＋ onto natural diatomite are Tenkin, Tenkin, Langmuir, Tenkin, Freundlich and Freundlich, respectively, the adsorption of each ion onto natural diatomite is mainly a physical process, and the adsorption reaction is favorable. It also can be found that, when using classical isothermal adsorption models to fit the experimental data in liquid/solid system, the equilibrium adsorption amount q＋ is not a single function of ion equilibrium concentration co, while is a function of two variables, namely co and the adsorbent concentration W0 , qo only depends on co/Wo. Results also show that the classical isothermal adsorption models have a significant adsorbent effect, and their parameter values are unstable, the simulation values of parameter differ greatly from the measured values, which is unhelpful for practical use. The tests prove that four-adsorption-components model can be used for describing adsorption behavior of single ion in nature diatomite-liquid system, its parameters k and qm have constant values, which is favorable for practical quantitative calculation in a given system.