New Trends in Separation Techniques of Lithium Isotopes: A Review of Chemical Separation Methods

In terms of isotopic technologies, it is essential to be able to produce materials with an enriched isotopic abundance (i.e., a compound isotopic labelled with (2)H, (13)C, (6)Li, (18)O or (37)Cl), which is one that differs from natural abundance. The isotopic-labelled compounds can be used to study different natural processes (like compounds labelled with (2)H, (13)C, or (18)O), or they can be used to produce other isotopes as in the case of (6)Li, which can be used to produce (3)H, or to produce LiH that acts like a protection shield against fast neutrons. At the same time, (7)Li isotope can be used as a pH controller in nuclear reactors. The COLEX process, which is currently the only technology available to produce (6)Li at industrial scale, has environmental drawbacks due to generation of Hg waste and vapours. Therefore, there is a need for new eco-friendly technologies for separation of (6)Li. The separation factor of (6)Li/(7)Li with chemical extraction methods in two liquid phases using crown ethers is comparable to that of COLEX method, but has the disadvantages of low distribution coefficient of Li and the loss of crown ethers during the extraction. Electrochemical separation of lithium isotopes through the difference in migration rates between (6)Li and (7)Li is one of the green and promising alternatives for the separation of lithium isotopes, but this methodology requires complicated experimental setup and optimisation. Displacement chromatography methods like ion exchange in different experimental configurations have been also applied to enrich (6)Li with promising results. Besides separation methods, there is also a need for development of new analysis methods (ICP-MS, MC-ICP-MS, TIMS) for reliable determination of Li isotope ratios upon enrichment. Considering all the above-mentioned facts, this paper will try to emphasize the current trends in separation techniques of lithium isotopes by exposing all the chemical separation and spectrometric analysis methods, and highlighting their advantages and disadvantages.