改性荔枝壳对Cr(Ⅵ)的吸附热力学研究

Adsorption Thermodynamic Characteristics of Cr(Ⅵ)on Modified Lychee Exocarp

以荔枝壳为原料,制备了羧甲基化改性荔枝壳(MLE)吸附剂,并对MLE吸附溶液中Cr(Ⅵ)的热力学进行了研究。结果表明,随着温度的升高,MLE对Cr(Ⅵ)的吸附量增大;随着Cr(Ⅵ)初始质量浓度的增加,MLE对Cr(Ⅵ)的吸附量也增大,当Cr(Ⅵ)初始质量浓度达到15 mg/L以后,吸附已基本达到饱和状态。Langumir等温方程能更好地解释MLE对Cr(Ⅵ)的吸附,该吸附属于单分子层吸附,吸附主要发生在MLE表面的活性位点。吸附热力学参数ΔG、ΔH和ΔS的计算结果表明,焓变ΔH和熵变ΔS都为正值,说明吸附过程吸热,温度越高,越有利于吸附的进行。在Cr(Ⅵ)初始质量浓度较低时,ΔG值为负值,说明MLE对Cr(Ⅵ)的吸附过程是一个自发的过程,且自发程度随着温度的升高而增大。吸附势随着吸附温度的升高而增大,表明升温对吸附有利。

Chloroacetic acid modified lychee exocarp was used as adsorbent for Cr（ Ⅵ） adsorption,and thermodynamic characteristics of the adsorption were discussed. Results showed that adsorption capacity of the modified lychee exocarp（ MLE） would increase with the increasing of temperature and Cr（ Ⅵ） initial concentration,when the Cr（ Ⅵ） initial concentration reached to 15 mg / L,the adsorption was basically in saturated state. Langmuir isothermal equation was better to explain the MLE adsorption of Cr（ Ⅵ）,this adsorption was a monolayer adsorption,mainly occurred on the active sites of MLE surface. Calculation results of the adsorption thermodynamic parameters namely ΔG,ΔH and ΔS showed that the enthalpy change ΔH and entropy change ΔS were positive,which indicating that the adsorption was an endothermic process,the higher the temperature,the more conductive to the adsorption. When in low initial Cr（ Ⅵ）concentration,the ΔG was negative,which indicating that the adsorption was a spontaneous process and the spontaneous degree would increase with temperature rising. Adsorption potential would increase with temperature rising,which indicating that the temperature rising was conducive to the adsorption.