| As a type of strategic energy metal in 21 st century, lithium stable isotopes of6 Li and7Li play important role in the new energy industry in the future. The separation of lithium isotopes was extremely difficult as 6Li and 7Li have the same extranuclear structure only with tiny mass differences. Crown ethers and cryptands having special selectivity of lithium ion were reported in the literature. The green extraction separation systems of lithium isotopes were designed in this article based on binaphthyl crown ether as extractant and ionic liquid as extraction medium, specific research contents include the following four aspects:1. 2,2’-binaphthyldiyl-17-crown-5(BN-17-5) and three kinds of hydrophobic imidazolium ionic liquids were synthesized, namely 3-octyl-1-methylimidazole hexaflorophosphate, 3-octyl-1-methylimidazole tetrafloroborate, 3-octyl-1-methylimidazole bistrifloromethylsulfonylimideand. Their compositions were further determined after the structure was charactered and analyzed by elemental analyses(EA), infrared spectra(IR),proton nuclear magnetic resonance(1HNMR) and mass spectrometry(MS).2. A novel liquid-liquid extraction system was established for the selective separation of lithium isotopes using BN-17-5 as extractant and imidazolium ionic liquids as extraction solvent. We investigated the effects of the concentration, initial p H and counter anion of lithium salt, BN-17-5 concentration, extraction temperature and time on the lithium isotopes separation. Under optimized conditions, the maximum extraction efficiency was 15.1%, the maximum single stage separation factor was 1.046 ± 0.002, indicating the lighter isotope 6Li was enriched in ionic liquids phase while the heavier isotope 7Li was concentrated in the solution phase. The formation of 1:1 complex Li(BN-17-5)+in the ionic liquids phase was determined on the basic of slope analysis method, and the mechanism of liquid-liquid extraction separation was investigated. Lithium ion in Li(BN-17-5)+ complex was stripped by1 mol L-1 HCl solution.3. A green solid-liquid extraction system was investigated for the separation of lithium isotopes using porous composite materials, doped with BN-17-5 and imidazolium ionic liquids, as solid adsorbent. The composite materials of mesoporous silica IL17-5SGs and impregnated resin IL17-5IRs were synthesized by sol-gel approch and direct impregnation process, respectively. Various extraction parameters such as the concentration of lithium salt,initial p H of aqueous phase, extraction time and the anion of lithium salt were optimized. The extraction separation behaviors of IL17-5SGs and IL17-5IRs to lithium isotopes are discussed and compared. The IL17-5IRs have higher extraction efficiency and shorter equilibrium time than IL17-5SGs. The study of thermodynamic parameters of systems indicated that the extraction process was spontaneous process and the temperature has less influence on the separation of lithium isotopes. Under optimized conditions, the maximum extraction efficiency was 15.86%, the maximum single stage separation factor was 1.048 ± 0.002,indicating the lighter isotope 6Li was enriched in the solid phase while the heavier isotope 7Li was concentrated in the solution phase. The corresponding optimized structures of lithium ion complexes were simulated, and the mechanism of solid-liquid extraction separation was intensively studied. The sorbents of IL17-5SGs and IL17-5IRs can be regenerated easily with HCl solution and reused repeatedly.4. In order to further improve the stability of composite materials, another solid-liquid extraction method was investigated for the separation of lithium isotopes using polymer resins as solid adsorbent. Merrifield resin acted as carrier, three kinds of polymer resins PSIL17-5s of BN-17-5-supported ionic liquid were prepared by covalent binding. Various factors were discussed and optimized with regard to their influence on the lithium isotopes separation, and the mechanism of extraction system was also studied. The thermodynamic parameters of the system were obtained by studying the effect of different temperatures on the extraction separation of lithium isotopes. Under optimized conditions, the maximum extraction efficiency up to 15.95%, the maximum single stage separation factor was 1.048 ± 0.002,indicating the lighter isotope 6Li was enriched in the solid phase and 7Li was concentrated in the aqueous phase. The recyclability studies manifest that the renewability and stability of PSIL17-5s is better than that of IL17-5SGs and IL17-5IRs. |
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