Preparation of ammonium tungstophosphate-calcium alginate composite adsorbent and adsorption thermodynamic and kinetic characteristics to rubidium

doi:10.11949/j.issn.0438-1157.20150505

Abstract

Abstract:

Heteropoly acid salt inorganic ion adsorbent which has good adsorption performance for alkali metal ions could be used for the separation or extraction of rubidium. A spherical composite adsorbent AWP-CaALG was prepared by sol-gel method with calcium alginate (CaALG) and ammonium tungstophosphate (AWP) which were as carrier and active component, respectively, and characterized by SEM, XRD, IR analysis. The adsorption capacity of the adsorbent toward rubidium was determined to be 43 mg·g^-1 under the optimum preparation conditions of m(NaALG):m(AWP)=1:2 and concentration of CaCl₂ of 0.5 mol·L^-1 with aging for 24 h and being dried at 105℃. The research of thermodynamic was carried out using Langmuir isotherm model and Freundlich isotherm model for description of experimental data. The free energy (ΔG), enthalpy (ΔH) and entropy (ΔS) changes of adsorption were evaluated. The result showed that the process of adsorption of Rb⁺ by AWP-CaALG could be described by Freundlich equation. The adsorption of Rb⁺ was spontaneous and exothermic process, and therefore, low temperature was advantageous to the adsorption. The study of kinetic was conducted using pseudo-first-order kinetic model, pseudo-second-order kinetic model and shell progressive model for description of kinetic data. The result showed that the adsorption of Rb⁺ could be described by the pseudo-second order kinetic model and was controlled by the chemical reaction.

Key words: rubidium, ammonium tungstophosphate, calcium alginate, adsorption, kinetic, thermodynamics

摘要：

杂多酸盐无机离子吸附剂对于碱金属离子具有良好吸附性能,可望用于铷的分离提取。以海藻酸钙(CaALG)为载体,对铷有良好选择性的磷钨酸铵(AWP)为活性成分,采用溶胶凝胶法制备球形复合吸附剂AWP-CaALG并优化了物料配比、CaCl₂浓度、陈化时间及干燥温度等制备条件,通过SEM、XRD、IR分析对制备产物进行了表征。通过静态吸附实验,测得吸附剂对Rb⁺吸附容量达43 mg·g^-1。实验考察了溶液中铷初始浓度、吸附温度对吸附过程的影响,分别采用Langmuir等温吸附模型、Freundlich等温吸附模型对实验数据进行线性回归分析,结果表明吸附过程更符合Freundlich等温吸附模型(R²>0.9962)。计算铷吸附过程焓变(ΔH)、熵变(ΔS)分别为-14.18 kJ·mol^-1和-0.0367 kJ·mol^-1·K^-1,不同温度下ΔG均为负值,说明该吸附过程可自发进行,低温利于吸附,升温利于解吸。吸附动力学结果表明该吸附过程符合拟二级动力学模型,且受化学反应控制。

关键词: 铷, 磷钨酸铵, 海藻酸钙, 吸附, 动力学, 热力学

CLC Number:

AN Lianying, ZHANG Chunxia, HUANG Xianjiang. Preparation of ammonium tungstophosphate-calcium alginate composite adsorbent and adsorption thermodynamic and kinetic characteristics to rubidium[J]. CIESC Journal, 2016, 67(4): 1378-1385.

安莲英, 张春霞, 黄献奖. 磷钨酸铵-海藻酸钙复合吸附剂的制备及其铷吸附热力学及动力学[J]. 化工学报, 2016, 67(4): 1378-1385.

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