玉米秸秆对废水中Cr(Ⅵ)吸附的热力学和动力学研究

Study on Thermodynamics and Kinetics of Adsorption of Cr(Ⅵ) in Wastewater by Corn Straw

利用玉米秸秆做吸附剂,通过批次实验对废水中Cr(Ⅵ)进行吸附研究,并用单因素实验方法讨论了体系pH值、玉米秸秆加入量、温度、废水中Cr(Ⅵ)的浓度、时间等条件对其吸附的影响,从而确定最佳吸附条件.实验还对其进行了吸附热力学、吸附动力学及等温吸附模型的研究.结果表明,最佳吸附条件为向50 mg·L^(-1)Cr(Ⅵ)的溶液中加入14 g·L^(-1)的玉米秸秆粉,在pH为1、吸附温度为30℃的条件下恒温搅拌3 h,其吸附效率达到最佳,去除率为92.91%.经吸附热力学分析在最佳条件下其吸附过程的△G<0、△H>0、△S>0,表明该吸附过程为自发的吸热过程.经吸附动力学研究可以看出其行为更好地符合Lagergren准二级动力学模型.用Langmuir和Freundlich模型对等温吸附数据进行拟合,发现Langmuir模型能更好反应吸附过程特征,且其最大饱和吸附量为3.903 3 mg·g^(-1).

The adsorption of Cr（Ⅵ） in wastewater was studied by batch experiments using corn stalk as adsorbent. The effects of pH, temperature, concentration of Cr（Ⅵ）, and time on the adsorption of the system were discussed by single factor experiment. In order to determine the optimal adsorption conditions,the experiments were carried out to study the adsorption thermodynamics, adsorption kinetics and isotherm adsorption model. The results show that to 50 mg·L^-1 Cr（Ⅵ） in the solution added 14 g·L^-1 of corn stalk powder at pH=1 as the optimum adsorption conditions, the adsorption temperature is 30 ℃ under the condition of constant temperature and stirred for 3 h, the adsorption efficiency achieves the best and removal rate was 92.91%. In the optimum conditions, the adsorption thermodynamics analysis the adsorption process △G0, △H0, △S0, it showed that the adsorption process was spontaneous and endothermic process.The study of adsorption kinetics can be seen that the behavior is better consistent with the Lagergren second-order kinetic model. Using Langmuir and Freundlich model to fit the isothermal adsorption data, it is found that the Langmuir model can be better to react to the characteristics of the adsorption process, and its maximum saturation adsorption amount is 3.903 3 mg·g^-1.