蛭石吸附Pb^(2+)的动力学和热力学机理研究

Research on the Kinetics and Isotherms for Lead(Ⅱ) Adsorption on Vermiculite

讨论了溶液pH值、温度对吸附平衡的影响,考察了吸附机理。结果表明,调节溶液pH=6.0,吸附时间30min,蛭石对浓度为10~160 mg/L Pb2+的吸附率超过99.0%,室温(10℃)下最大吸附容量为87.72 mg/g。吸附动力学可用拟二级速率方程来描述,计算值与实测值吻合甚好,相关系数达到0.9999。蛭石对Pb2+的吸附等温线明显分为两段,在Pb2+浓度为200~500 mg/L范围内,吸附平衡符合Langmuir和Freundlich方程,室温下相关系数分别达到0.992和0.998。温度升高,吸附平衡量增大,表明该吸附反应是吸热反应,求出反应的焓变ΔH=4.02 kJ/mol,熵变ΔS=27.41 J/(mol.K),吉布斯自由能变化ΔG分别为-3.74(10℃)-、4.46(35℃)-、5.01(60℃)、-5.72(80℃)kJ/mol。

The adsorption ratio of Pb^2＋ with concentrations of 10 to 160 mg/L on the venniculite is more than 99.0 %, and the maximal sorption capacity is 87.72 mg/g under the conditions of adsorption for 30 min and pH = 6.0. Pseudo second order model best describe the reaction rate, adsorption capacity calculated by the model is consistent with that actual measurement, which the correlation coefficient（r） is 0. 9999. The adsorption isotherms of Pb^2＋ with different temperature are divided to two parts. The experimental data with Pb^2＋ concentrations from 200 to 500 mg/L follow both Langmiur and Freundlich isotherm model, which r is 0. 992 and 0. 998 respectively at 10 ℃. The equilibrium adsorption capacity increases with increasing temperature from 10 to 80 ℃, which indicates that the adsorption process is endothermic. For the adsorption process, the enthalpy is 4.02 kJ/mol, the entropy is 27.41 J/（mol·K）, and the free energy is -3.74 （10 ℃ ）, -4.46 （35 ℃ ）, -5.01 （60 ℃ ）, -5.72 （70 ℃ ） kJ / mol respectively.