Study On The Separation Of Lithium Isotopes By Inorganic Ion Exchangers

The lithium element is composed of two stable isotopes 6Li and 7Li and both of them have important applications in fundamental material and nuclear science. Especially6 Li which can produce the tritium by neutron bombardment, is the essential raw material to realize the tritium fusion reaction. Therefore, the separation of lithium isotopes has important implications for the future of energy. In this paper, we obtained the inorganic ion exchangers based on the precursors of lithium ion conductors to study their exchange properties and lithium isotope separation abilities. The specific contents are as follows:1. The perovskite-type lithium lanthanum titanate of Li0.36La0.55 Ti O3(LLTO) has been synthesized by solid-state reaction method. Sr2+, Al3+ were doped in the LLTO to obtain Li0.36La0.55Sr0.03 Ti O3(LLSTO) and Li0.36La0.56Ti0.97Al0.03O3(LLTAO). Inorganic ion exchangers H0.36La0.55 Ti O3(HLTO), H0.36La0.55Sr0.03 Ti O3(HLSTO) and H0.36La0.56Ti0.97Al0.03O3(HLTAO) has been prepared by acid treatment of the three precursors.All the three ion exchangers showed high selectivity toward Li+ ion and low affinity toward alkali metal ions of larger radius like K+, Rb+and Cs+. HLTO, HLSTO and HLTAO showed well ion exchange performance by the discussions of the aqueous p H, concentration of Li+and equilibrium time. The uptaken values of Li+were 1.85, 1.91 and 1.78 mmol g-1under the optimized conditions, respectively, which have attained 90% of the theoretical exchange capacity values. The thermodynamic parameters indicated that the ion exchange process was a spontaneous exothermic process. The lighter isotope 6Li was enriched in ion exchanger phase while the heavier isotope7 Li was concentrated in the solution phase. The maximum single-stage separation factors of lithium isotopes, S, were 1.042, 1.040 and 1.045 for HLTO,HLSTO and HLTAO, which were higher than manganese ion exchangers. The structures of three ion exchangers were stable and they can be reproducible and recyclable for lithium isotopes separation, which were better than zirconium titanium phosphate ion exchangers.2. Two kinds of lithium titanium oxide was synthesized by solid-state reaction method:ramsdellite type Li2Ti3O7(LTO7) and spinel Li4Ti5O12(LTO12), and the different content of Al3+ were doped in the latter to obtain Li3.95Al0.05Ti5O12(LATO-0.05) and Li3.95Al0.1Ti5O12(LATO-0.1). Inorganic ion exchangers H2Ti3O7(HTO7), H4Ti5O12(HTO12), H3.95Al0.05Ti5O12(HATO-0.05) and H3.95Al0.1Ti5O12(HATO-0.1) were obtained by hydrogenation of the precursors. The exchangers were Li+-specific and the aqueous p H, Li+concentration and ion exchange rate were discussed which indicated that HTO7, HTO12, HATO-0.05 and HATO-0.1had well ion exchange performance. The Li+uptake values were 5.83, 7.31, 7.03 and 6.93 mmol g-1 under the optimized conditions, which were above 80% of the theoretical exchange capacity values. The maximum single-stage separation factors of lithium isotope of exchangers were 1.035, 1.037, 1.039 and 1.042. The thermodynamic parameters indicated that the ion exchange process was a spontaneous exothermic process and the temperature had little effect on the separation of lithium isotopes. Recycle experiments showed that the exchangers can regenerated and recycling.3. Garnet type Li5La3Nb2O12(LLNO) was synthesized by solid-state reaction method and the inorganic ion exchanger H5La3Nb2O12(HLNO) was obtained by acid treatment. The exchanger has high selectivity for Li+, and smaller affinity for Rb+, K+ and Mg2+. The aqueous p H, Li+concentration and ion exchange rate were discussed which indicated that HLNO had well ion exchange performance. The Li+ uptake value reached 5.12 mmol g-1 under the optimized conditions, which have attained 85% of the theoretical exchange capacity value.Thermodynamic study of the system showed that the ion exchange process was a spontaneous process. The largest single stage separation factor of HLNO was 1.043, which indicated that6Li+ was enriched in the exchanger phase and 7Li+ was concentrated in the solution phase.Recycle experiments showed that the exchangers can regenerated and recycling for ion exchange and lithium isotopes separation.