Green and efficient extraction strategy to lithium isotope separation with double ionic liquids as the medium and ionic
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Green and efficient extraction strategy to lithium isotope separation with double ionic liquids as the medium and ionic associated agent Xu Jingjing • Li Zaijun • Gu Zhiguo Wang Guangli • Liu Junkang
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Received: 21 August 2012 / Published online: 27 September 2012 Ó Akade´miai Kiado´, Budapest, Hungary 2012
Abstract The paper reported a green and efficient extraction strategy to lithium isotope separation. A 4-methyl10-hydroxybenzoquinoline (ROH), hydrophobic ionic liquid—1,3-di(isooctyl)imidazolium hexafluorophosphate ([D(i-C8)IM][PF6]), and hydrophilic ionic liquid—1-butyl3-methylimidazolium chloride (ILCl) were used as the chelating agent, extraction medium and ionic associated agent. Lithium ion (Li?) first reacted with ROH in strong alkali solution to produce a lithium complex anion. It then associated with IL? to form the Li(RO)2IL complex, which was rapidly extracted into the organic phase. Factors for effect on the lithium isotope separation were examined. To obtain high extraction efficiency, a saturated ROH in the [D(i-C8)IM][PF6] (0.3 mol l-1), mixed aqueous solution containing 0.3 mol l-1 lithium chloride, 1.6 mol l-1 sodium hydroxide and 0.8 mol l-1 ILCl and 3:1 were selected as the organic phase, aqueous phase and phase ratio (o/a). Under optimized conditions, the single-stage extraction efficiency was found to be 52 %. The saturated lithium concentration in the organic phase was up to 0.15 mol l-1. The free energy change (DG), enthalpy change (DH) and entropy change (DS) of the extraction process were -0.097 J mol-1, -14.70 J mol K-1 and -48.17 J mol-1 K-1, indicating a exothermic process. The partition coefficients of lithium will enhance with decrease of the temperature. Thus, a 25 °C of operating temperature was employed for total lithium isotope separation process. Lithium in Li(RO)2IL was stripped by the sodium chloride of 5 mol l-1 with a phase ratio (o/a) of 4. The lithium isotope exchange reaction in the interface
X. Jingjing L. Zaijun (&) G. Zhiguo W. Guangli L. Junkang School of Chemical and Material Engineering, Jiangnan University, Wuxi 214122, China e-mail: [email protected]
between organic phase and aqueous phase reached the equilibrium within 1 min. The single-stage isotope separation factor of 7Li–6Li was up to 1.023 ± 0.002, indicating that 7Li was concentrated in organic phase and 6Li was concentrated in aqueous phase. All chemical reagents used can be well recycled. The extraction strategy offers green nature, low product cost, high efficiency and good application prospect to lithium isotope separation. Keywords Lithium Isotope separation Ionic liquid Solvent extraction
Introduction Lithium consists of 6Li and 7Li two stable isotopes in nature. Li can be cracked into tritium (T) and helium (He) by bombarding with neutron, thus 6Li was used as nuclear raw materials for hydrogen bomb to rapidly proferate T, protective materials of neutron for fission reactor to absorb neutron, and fuel for fusion power reactor to proferate T. Unlike 6Li, 7Li can not absorb neutron an
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