Lithium is an alkali metal that can be found in several hard rock types, including spodumene and salt lakes. It is a light element with an atomic mass of 6.941 amu.
7 li (pronounced seven-lime) is the most abundant of the stable lithium isotopes. It has a relative atomic mass of 6.941 amu, which is close to the corresponding mass for its lighter isotope 6Li (average atomic weight of 6.06 amu).
The most prominent uses for 7Li are as a hydroxide and as a fluoride in pressurised water reactors for controlling the chemistry of coolant systems, and as a component of the fluoride coolant in molten salt reactors. However, the isotope also has many other useful applications in nuclear energy and research, notably as a source of tritium, which is essential for fusion to occur.
Despite their widespread abundances in nature, lithium isotopes are susceptible to significant fractionation in natural processes due to their relatively large difference in mass. This has implications for geochemistry and cosmochemistry, as well as in nuclear science and biomedical sciences. As a result, lithium is often difficult to extract for laboratory purposes. In the past, significant efforts have been made to develop high-precision methods for separating lithium isotopes from each other. The most successful techniques for isotope separation include atomic vapour laser isotope separation (AVLIS), and high-temperature ion exchange, both of which are now commercially available. The AVLIS method is particularly suitable for small quantities of pure Li-7 that are required for PWR cooling systems.