Fractional crystallization, high-lithium

Several alternative methods proposed for lithium recovery from seawater use ion exchange after solar evaporation and fractional crystallization of NaCl, CaS04 and KCl MClj. In these instances, polymeric ion exchangers, such as highly cross-linked Dowex 50 (16% DVB) [110] or Retardion Ag II, A8 (copolymer of styrene and acrylic acid cross-linked... 

The principal commercial source of rubidium is accumulated stocks of a mixed carbonate produced as a byproduct in the extraction of lithium salts from lepidohte. Primarily a potassium carbonate, the byproduct also contains ca. 23 wt.% rubidium and 3 wt.% cesium carbonates. The primary difficulty associated with the production of either pure rubidium or pure cesium is that these two elements are always found together in nature and also are mixed with other alkali metals because these elements have very close ionic radii, their chemical separation encounters numerous issues. Before the development of procedures based on thermochemical reduction and fractional distillation, the elements were purified in the salt form through laborious fractional crystallization techniques. Once pure salts have been prepared by precipitation methods, it is a relatively simple task to convert them to the free metal. This is ordinarily accomplished by metallothermic reduction with calcium metal in a high-temperature vacuum system in which the highly volatile alkali metal is distilled from the solid reaction mixture. Today, direct reduction of the mixed carbonates from lepidolite purification, followed by fractional distillation, is perhaps the most important of the commercial methods for producing rubidium. The mixed carbonate is treated with excess sodium at ca. 650 C, and much of the rubidium and cesium passes into the metal phase. The resulting crude alloy is vacuum distilled to form a second alloy considerably richer in rubidium and cesium. This product is then refined by fractional distillation in a tower to produce elemental rubidium more than 99.5 wt.% pure. 

Fig. 4 Distribution of 1,312 lithium oxides extracted from the ICSD database with respect to fractional accessible volume of the crystal structure space with bond valence mismatch of less than 0.2 valence units. The histogram bin size is 0.001. According to Avdeev et al. [10], structures with high values of the fractional accessible volume per ion of the mobile species may be expected to have high ionic conductivity...

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