Metal distillation

It occurs chiefly as cinnabar, the red sulphide HgS, from which it is readily extracted either by roasting (to give the metal and sulphur dioxide) or by heating with calcium oxide the metal distils off and can be purified by vacuum distillation. 

The T dependence of the solubility of CsH in Cs differs significantly from those for solutions of the hydrides in the other alkali metals. Distillation leaves behind involatile impurity salts, but oxygen transport from distilland to receiver has been observed. Oxygen can be carried over with the distillate in the form of COj or CO, the former being produced by decomposition of carbonate and the latter by reduction of oxides with a carbon impurity under dry conditions near the end of distillation. The identification of CO among the noncondensable gases during the distillation of Cs lends support to this. ... 

Nonmetallic impurities, mostly oxygen, found in actinide metals distilled under a vacuum of 0.1 mPa range from 4000 to 7000 atomic ppm. In a vacuum of 0.1 Pa the nonmetallic impurity content decreases to between 400 and 880 atomic ppm (51, 52). 

At the present time, when gram to kilogram amounts of either Am isotope are available, the method of choice for the preparation of Am metal is the metallothermic reduction of Am02 with La (or Th) using a pressed pellet of the oxide and the reductant metal. An oxide reduction-metal distillation still system is shown schematically in Fig. 11. Yields of Am metal are typically >90% and purity levels equal or exceed 99.5 at %. Further purification of the product Am metal can be achieved by repeated sublimations under bigh vacuum in a Ta apparatus (Section III,B Fig. 4). A photograph of 2 g of Am metal distilled in a Ta apparatus is given in Fig. 12. 

Fig. 11. An oxide reduction-metal distillation still system.

Indium may be recovered from zinc ores by several patented processes. Usually it is recovered from residues obtained from zinc extraction. The residues, slags, fume, or dusts from zinc smelting or lead-zinc smelting are treated with a mineral acid. Other steps involved in recovery often vary, but mostly use solvent extraction and precipitation steps. In some processes, treatment with caustic soda yields indium hydroxide. The hydroxide is calcined to obtain oxide, which then is reduced with hydrogen at elevated temperatures to obtain the metal. Distillation or electrolysis are the final steps to... 

The checkers used tetrahydrofuran which was distilled from lithium aluminum hydride (Caution see Org. Synth., Collect. Vol. V 1973, 976) and stored with a chip of sodium metal. Distillation from sodium/benzophenone is preferable. 

Commercial tetrahydrofuran, purchased from British Drug House (Canada) Ltd. or Fisher Scientific Company, was refluxed over sodium metal, distilled from sodium metal, then redistilled from lithium aluminum hydride under a nitrogen atmosphere. 

Zinc.—The chief ore of zinc is the sulphide. To convert it into the oxide, it is roasted on a flat hearth in a current of air 2ZnS + 302= 2ZnO + 2S02. The oxide is mixed with small coal (slack) and placed in cylindrical retorts of fireclay. These retorts have pipes of rolled sheet-iron luted to the open ends with fireclay they are packed into a furnace in tiers, and the temperature is raised to bright redness. The coal distils first, giving off coal-gas, which expels air from the retorts. When the temperature exceeds 1000% the zinc distils and condenses in the iron pipes. It happens that almost all zinc ores contain cadmium sulphide, which, like zinc sulphide, is converted into oxide by roasting and on distillation, the cadmium, which is the more volatile metal, distils over first and condenses in the outer portion of the tubes. These are untwisted and the metal removed with a chisel. 

An older metallurgical process, which is still used extensively, involves a rather extended treatment of high-grade ore or concentrates obtained by a flotation process. In either case, the finely divided ore is roasted to convert sulfides and carbonates to oxides, which are then reduced by means of carbon at temperatures of 1200 to 1300°C. Since zinc boils at 907°C, the liberated metal distills from the earthenware retort and may be condensed in suitable receivers. If the temperature of the condenser is kept below the melting temperature of zinc (419.3°C), the metal is obtained in the form of zinc dust which, in addition to metallic impurities, contains approximately 5% zinc oxide. If, however, the zinc vapors are condensed at a temperature above... 

Since the alkali metals as a class are the strongest chemical reducing agents known, they cannot be prepared by chemical reduction without trie enforcement of a heavy shift in equilibrium conditions as an example, small quantities of sodium metal may be prepared by reducing sodium chloride with calcium metal, distilling away the sodium metal as it is formed. 

The major ore of zinc (though it occurs in numerous other minerals) is sphalerite, a form of ZnS usually found to also contain iron and commonly associated with galena (PbS). Cadmium is mostly found isomorphously replacing zinc in zinc minerals. To obtain metallic zinc from its ore, the ore is first calcined to ZnO and this is then roasted at ca. 1000°C with charcoal in the absence of air, whence the metal distills out. Cadmium can be separated from sulfate solutions of both zinc and cadmium by addition of zinc dust ... 

Jb) Low volatility Certain metal tubes are undesirable at high temperatures because the metal distils upon the couple, thus altering its calibration. 

Volatilization. Many fission-product elements, including krypton, xenon, iodine, cesium (normal boiling point 705 C), strontium (1380°C), barium (1500°C), the rare earths (3200 C), and plutonium (3235°C), are more volatile than uranium (3813°C). Cubicciotti [C17], McKenzie [M5], and Motta [M8], in laboratory experiments, showed that around 99 percent of these more volatile elements could be separated from uranium by vacuum distillation at 1700 C. Because of the high temperature and severe materials problems, volatilization has not been used as a primary separation process, but does contribute to removal of the most volatile fission products in conventional reprocessing. In fractional crystalUzation or extraction with liquid metals, distillation is used to separate uranium and plutonium from more volatile solvent metals. 

Because of the relatively high vapor pressure of the alkali metals compared with most other metals, distillation is an acceptable method of purification. Distillation under reduced pressure lowers the distillation temperature and thereby reduces the risk of contamination from the condenser. Vapor pressures increase from lithium to cesium (Table I). In the case of cesium (and also rubidium), the vapor pressure is sufficiently high that the type of glass still used for molecular liquids (e.g., water or alcohol) can be used for the alkali metal also. Removal of transition metals by distillation is virtually complete. With cesium, the high solubility of oxygen renders the filtration method unsuitable, whereas distillation is efficient. 

In principle, distillation can be carried out over a wide range of pressures, spanning the extremes of near-total vacuiun and the critical point. While atmospheric distillation is the preferred mode of operation, r uced pressures offer the advantage of lower temperatures and energy requirements. They are often employed to avoid thermal degradation of heat-sensitive materials (ethylbenzene/styrene distillation) or are forced upon the operator by the low vapor pressme of the charge (metal distillation). The drawbacks of this mode of operation are the obvious cost and inconvenience... 

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