苯并15-冠-5醚接枝壳聚糖薄膜分离锂同位素性能研究

Preparation of Chitosan Graft 4'-Formoxylbenzo-15-crown-5-ether Film for Lithium Isotopes Adsorptive Separation

以壳聚糖与4'-甲酰基苯并-15-冠-5醚为原料,通过希夫碱反应制备了苯并-15-冠-5醚接枝壳聚糖薄膜,采用固-液萃取法研究薄膜吸附锂离子动力学和热力学行为,及其锂同位素吸附分离性能.结果表明:冠醚接枝壳聚糖薄膜对锂离子的吸附过程更加适合于准二级动力学方程和Langmuir吸附等温模型,薄膜对锂离子的吸附是一个由化学吸附控制的单层表面吸附,是一个自发进行的放热过程.此外以水-碘化锂/冠醚接枝壳聚糖薄膜(冠醚固载量为2.98 mmol/g)作为萃取体系,其单级分离因子高达1.053(10oC).且轻同位素6Li富集于薄膜相,重同位素7Li富集于液相.

Thecrown ethers show good efficiency for lithium isotope separation due to their high affinity and size selectivity for lithium ions. A chitosan （CTS） graft 4＇-formoxylbenzo- 15-crown-5-ether （FB 15C5） （CTS-g-FB 15C5） film was synthesized from chitosan and FB15C5 via Schiff reaction. The structure of CTS-g-FB15C5 film was analyzed through XPS analysis. The solid-liquid extraction was used to study the lithium ion adsorption kinetics, adsorption thermodynamics and lithium isotope separation effect of the CTS-g-FB 15C5 films. Meanwhile, the effect of immobilization amount of crown ether on CTS and extraction temperature on single stage separation factor were also explored. The results showed that pseudo-second-order kinetic model and Langmuir isotherm model were more favorable to describe the process of lithium ions adsorption on CTS-g-FB 15C5 film with the immobilization amount of crown ether of 2.98 mmol/g. It indicated that the Li＋ ions adsorption carried out with CTS-g-FB15C5 film exhibited the typical chemical adsorption and the monolayer adsorption. The thermodynamics parameters, such as Gibbs free energy （AG）, enthalpy change （AH） and entropy change （AS）, indicated that Li^＋ ions adsorption on the film was spontaneous, exothermic and random. Furthermore, the single stage separation factor decreased from （1.053 ± 0.002） to （1.012 ± 0.001） with the increase of extraction temperature from 10 ℃ to 30 ℃ during the solid- liquid extraction for lithium isotopes separation using CTS-g-FB15C5 film. The single stage separation factor increased from （1.042 ± 0.002） to （1.053 ± 0.002） with the increasing immobilization amount of crown ether from 1.10 mmol/g to 2.98 mmol/g. The maximum value of single stage separation factor obtained from the extraction system of H20-LiI/CTS-g-FB 15C5 film at 10 ℃ was up to （1.053 ± 0.002）, which was higher than an acceptable single stage separation factor of 1.03 in a large scale. In addition, it was found that light isotope （6Li） was concentrated in the film, whereas the heavy isotope, 7Li, was enriched in the solution. In sum, the produced CTS-g- FB 15C5 films have a good potential prospect in lithium isotope adsorptive separation.