リチウム資源—各鉱床タイプの概要とリチウム同位体による成因論—

抄録

Lithium, one of the ‘rare metals’ defined by Japanese government, is industrially important, and Li compounds are used for many purposes (e.g., Li-ion batteries). The major types of lithium deposits are (1) brine, (2) pegmatite, and (3) sedimentary deposits. Because of the low production costs for Li in brine deposits, they account for approximately 60% of identified worldwide Li resources and for approximately 70% of worldwide Li production. Recent increases in Li production, an expected high demand for its use in eco-friendly cars, and uneven distribution of Li-producing countries underline the importance of maintaining a stable Li supply. Therefore, more brine deposits should be exploited, and the development of other types of Li deposits should be explored.
  Lithium carbonate is extracted from brine deposits in playas and salt crusts by exploiting the solubility differences of different ionic compounds. Li-rich brine deposits probably form by orographic/topographic effects and by local hydrothermal activity, because Li is a fluid-mobile element and its elution from solids into fluids is temperature dependent. Lithium-pegmatite deposits probably form by intermittent intrusions of pegmatite magma in which Li has become concentrated by the addition of Li-rich differentiates from felsic magma, because Li is a moderately incompatible element. Sedimentary-type Li deposits, which are composed of hectorite and jadarite, are still relatively undeveloped, but they are attracting a great deal of attention as possible new Li resources. In addition to these sources, methods to extract Li from seawater and to reclaim Li by urban mining of discarded products have also been examined.
  Lithium isotope analysis is a powerful tool for tracing water-rock interactions and for investigating various geochemical and geological processes. Moreover, the origin of Li and the history of Li accumulation in Li deposits can often be determined from its isotopic signature.