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LITHIUM
Natural Abundance, Stable Isobars Li6, 7.42%, None Li7, 92.58% Lithium chloride, lithium bromide, lithium iodide, and mixtures of the bromide or chloride with lithium metal have been used as charge material for the separation of the isotopes of lithium. From an operational, as well as an economical standpoint, a mixture of one part by weight Li metal and ten parts by weight LiCl forms the best charge material. The usual charge consists of 175 g LiCI-Li metal in a style C-18 graphite charge bottle. The various halides of lithium are available commercially; but, since lithium of exceptional purity or with enhanced isotopic content was available for these separations, the halides were prepared in the laboratory. Materials having these special qualities were used and the unresolved feed material was recovered from the calutron. Preparation of the halides of lithium consists of carefully dissolving lithium metal in water contained in a plastic beaker. After filtering, the solution is acidified with the appropriate acid, evaporated to incipient crystallization, and allowed to cool, at which time it solidifies. (Lithium salts should not be allowed to go to dryness in an evaporating dish since removal of the cake without breaking the dish becomes exceedingly difficult.) The solids are carefully removed, placed in an outgassing apparatus, and dehydrated at 400° C. Plastic containers are used whenever the lithium solution is basic to prevent sodium contamination from glassware. Unresolved lithium charge material is recovered by washing the calutron components with dilute hydrochloric acid. The wash solution is filtered to remove any insoluble material and then is saturated with hydrogen sulfide. After filtering and washing the precipitate, which is discarded, the solution is made basic with ammonium hydroxide and again saturated with hydrogen sulfide. Filtering removes the precipitate which is washed and discarded. The solution is acidified with hydrochloric acid and boiled to agglomerate sulfur, which is removed by filtration. Upon evaporating the solution to dryness, a mixture of ammonium chloride and LiCl salts is obtained. Ammonium chloride is removed by heating the mixture to 450° C under vacuum. The remaining LiCl is fused by induction heating in a nickel container under an inert atmosphere. When cool, the fused crystalline mass of LiCi is broken out of the container and stored in sealed bottles. Lithium metal in air ignites at 90° C and burns violently; therefore, it must not be exposed to flame or heat except under controlled conditions. Lithium metal reacts with water, releasing hydrogen which can form an explosive mixture with air. The salts of lithium are not considered dangerous chemicals although the do have poisonous effects if ingested. Lithium dissolved in water forms lithium hydroxide, which is caustic and can cause burns on the skin and mucous membranes similar to those produced by sodium hydroxide. Safety precautions for the handling of lithium and its compounds include the use of safety glasses or face shield, rubber gloves, and respirators, particularly if dusting occurs. The metal should not be inadvertently exposed to air, heat, or moisture. |
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