Preparation Of Crown Ether Grafted Chitosan/polyvinyl Alcohol Blend Membrane Material And Its Lithium Isotope Separation Performance

Natural lithium consists of two isotopes(6 Li 7.5%and 7Li 92.5%),which play an important pole in the development of nuclear fusion.The technology of lithium isotope separation is the key to solve the problem of nuclear power development and applications and relative to the implementation of the national energy security and the sustainable development strategy.Therefore,the aim of the present study is to prepare crown ether grafted chitosan membranes for lithium isotope separation so as to provide the base for the construction of membrane chromatography.CTS-g-B15C5 polymer with the immobilization amount of crown ether of 2.98 mmol/g was prepared by Schiff reaction between chitosan and 4'-formylbenzo-15-crown-5-ether.A solid-liquid extraction method was used to study lithium isotope separation property of the obtained CTS-g-B15C5 films.The distribution coefficient decreased from 6.68 mL/g to 3.45 mL/g and the single stage separation factor decreased from 1.059±0.001 to 1.012±0.002 with the increase of temperature from 0? to 30?.The maximum distribution coefficient and the single stage separation factor were 6.98 mL/g and 1.053±0.001 using the lithium iodide as the lithium salt.The distribution coefficient increased from 2.11 mL/g to 5.04 mL/g with an increase in the immobilization amount of crown ether increased from 1.10 mmol/g to 2.98 mmol/g.At the same time,the single stage separation factor increased from 1.042±0.002 to 1.053±0.002 with the increasing of immobilization amount of crown ether.The light isotope,6Li,was enriched in film phase,whereas,the heavy one,7Li,was enriched in solution phase.In addition,the static adsorption method was used to study kinetics and thermodynamics for lithium ions adsorption of CTS-g-B15C5 films.The results showed that the equilibration time increased from 40min to 60min with the increase of the original lithium ions concentration.The pseudo-second-order reaction kinetic model and Langmuir isotherm model are more favorable the adsorption process of lithium ions on CTS-g-FB15C5.Meanwhile,the thermodynamics parameters such as free energy change(?G),the enthalpy change(?H)and entropy change(?S)indicated the lithium adsorption onto CTS-g-B15C5 polymers was spontaneous,exothermic and randomness.Finally,crown ether grafted chitosan(CTS-g-FB15C5)/polyvinyl alcohol(PVA)blend micro-porous membrane with sponge-like pore structure was prepared by immersion precipitation phase inversion.The mechanical property was enhanced by blending with PVA and the stability of the blending membranes was improved after crosslinking with glutaraldehyde.A dynamic adsorption method was used to study lithium isotope separation performance of CTS-g-FB15C5/PVA blend membrane.The results indicated that the distribution coefficient increased from 68.6 mL/g to 174.96 mL/g with the increase of mean membrane pore size from 0.536 ?m to 0.982?m.However,it decreased from 174.96 mL/g to 149.3 mL/g with further increase of mean pore size from 0.982 ?m to 1.073 ?m.At the same time,the distribution coefficient increased from 80.16 mL/g to 186.70 mL/g and the single stage separation factor increased from 1.008±0.002 to 1.046±0.002 with the increase of the immobilization amount of crown increased from 1.07 mmol/g to 2.60 mmol/g.