Preparation Of Azacrown Ether Grafted Polysulfone/nonwoven Fabric Composite Membrane And Its Lithium Isotope Separation Performance

In nature,the lithium has lithium-6?6Li?and lithium-7?7Li?two stable isotopes with relative abundance of 7.43%and 92.57%,respectively.These two isotopes of lithium play crucial roles in the nuclear industry.The neutron bombards 6Li can generate tritium?T?and helium?He?.7Li is commonly used as a pH controller and coolant in nuclear fusion reactions.In this paper,the crown ether was immobilized on the polymer by the chemical grafting method.Meanwhile,the polymer solution was directly used as casting solution for composite membrane preparation by non-induced phase separation?NIPS?.Furthermore,the adsorption and separation performance of lithium isotopes were systematically explored with the composite membrane as extractant.Firstly,Polysulfone-graft-monoazabenzo-15-crown-5 ether/non-woven fabrics?PSf-g-BN 15C5/NWF?composite membrane was prepared for lithium isotopes separation by NIPS.The effects of non-woven fabrics,polymer concentration,additive and coagulation bath temperature on membrane properties were systematically explored.The results demonstrated that the composite membrane had a uniform sponge-like pore structure with a porosity of 69%,pure water flux of 1433 L·m^-2·h^-1 and a carbon ink rejection of 78%when the polymer concentration was 14 wt.%,the additive was polyvinylpyrrolidone?PVP-K30?with 8 wt.%,water as the coagulation bath at 60 ?.In addition,the PSf-g-BN15C5 flat membrane was fabricated under the same conditions of PSf-g-BN15C5/NWF composite membrane.The porosity and pure water flux were 82%and 1060 L·m^-2·h^-1,respectively.The breaking strength of the composite membranes was 15.4 MPa.The mechanical property was much higher than those of PSf-g-BN15C5 flat membrane,commercial SPSf and PVDF membranes as well as pure non-woven fabrics.Secondly,the adsorption kinetics and thermodynamics of PSf-g-BN15C5/NWF composite membrane on lithium ion were explored by dynamic adsorption method.The calculated adsorption capacity of the PSf-g-BN15C5/NWF composite membrane at adsorption equilibrium was in good agreenment with the actual value by the Lagrange pseudo-second-order adsorption kinetic model,indicating that the adsorption process was a typical chemical adsorption.The adsorption thermodynamics fitted the Freundlich isotherm model,showing that the adsorption belongs to the multi-molecular layer adsorption.The free energy??G?,enthalpy??H?and entropy??S?were negative,indicating that the adsorption of lithium ions was a spontaneous exothermic process by the PSf-g-BN15C5/NWF composite membrane.Meanwhile,the PSf-g-BN15C5 flat membrane was used for adsorption of lithium ion.the adsorption reached equilibrium when the extraction time was 30 min.The maximum distribution coefficient?K_d?and adsorption capacity?q?were 169 mL·g^-1 and 0.456 mg·g^-1,respectively.Finally,PSf-g-BN15C5/NWF composite membrane was used as the extractant for lithium isotopes separation by solid liquid extraction system.The effects of extraction time,crown ether immobilization amount and the extraction systems were investigated,respectively.The results showed that the adsorption capacity of lithium ions reached the equilibrium when the extraction time at 100 min.The distribution coefficient and separation factor?a?were 16.01 mL·g^-1 and 1.052 ± 0.002 when the crown ether immobilization amount was 0.81 mmol·g^-1.The separation factor was higher than the traditional liquid-liquid extraction system of H₂O-LiI/BN15C5-CHCl₃?1.007 ± 0.002?and solid liquid extraction system of H₂O-LiI/PSf-g-BN15C5?1.014±0.002?for lithium isotope separation.In brief,PSf-g-BN 15C5/NWF composite membrane has a great potential application in the development of lithium isotopes adsorptive separation.