Metal elemental tellurium

Sulphur is less reactive than oxygen but still quite a reactive element and when heated it combines directly with the non-metallic elements, oxygen, hydrogen, the halogens (except iodine), carbon and phosphorus, and also with many metals to give sulphides. Selenium and tellurium are less reactive than sulphur but when heated combine directly with many metals and non-metals. 

Manufacture and Recovery. Electrolytic copper refinery slimes are the principal source of selenium and its sister element, tellurium, atomic numbers 34 and 52, respectively. Electrolytic copper refinery slimes are those constituents in the copper anode which are not solubilized during the refining process and ultimately accumulate in the bottom of the electrorefining tank. These slimes are periodically recovered and processed for their metal values. Slimes generated by the refining of primary copper, copper produced from ores and concentrates, generally contain from 5—25% selenium and 2—10% tellurium. 

The SeBr which forms is distilled from the solution leaving the interfering elements behind. The only other metallic elements that can also distill over by this procedure are arsenic, antimony, tellurium (pardy), and germanium. 

Although this procedure yields tellurium as the same compound found in the original feedstock, the copper teUuride is recovered in a comparatively pure state which is readily amenable to processing to commercial elemental tellurium or tellurium dioxide. The upgraded copper teUuride is leached with caustic soda and air to produce a sodium teUurite solution. The sodium teUurite solution can be used as the feed for the production of commercial grade teUurium metal or teUurium dioxide. 

Elemental tellurium and the stable teUurides of heavy nonferrous metals are relatively inert and do not represent a significant health hazard (43—47). Other, more reactive teUurides, including soluble and volatile teUurium compounds such as hydrogen teUuride [7783-09-7] teUurium hexafluoride [7783-80-4] and alkyl teUurides, should be handled with caution. Some of these materials can enter the body by absorption through the skin or by inhalation and ingestion of dust or fumes. No serious consequences or deaths have been reported in workers exposed to teUurium and its compounds in industry (48). 

Since tire alkali and alkaline metals have such a high affinity for oxygen, sulphur aird selenium they are potentially useful for the removal of these iron-metallic elements from liquid metals with a lower affinity for these elements. Since the hairdling of these Group I and II elements is hazardous on the industrial scale, their production by molten salt electrolysis during metal rehning is an attractive alternative. Ward and Hoar (1961) obtained almost complete removal of sulphur, selenium and tellurium from liquid copper by the electrolysis of molten BaCla between tire metal which functioned as the cathode, and a graphite anode. 

In the anion electrochemical series, sulfur, being the less noble element compared to its heavier congeners, occupies an intermediate position between iodine and selenium [(+)F, Cl, Br, I, S, Se, Te(-)]. Selenium, regarded as a metalloid, is a relatively noble element. Tellurium is rather an amphoteric element it can enter into solution in the form of both cations and anions. Regarded as a metal, i.e., with respect to its cations, tellurium occupies a position between copper and mercury. Regarded as a metalloid, i.e., with respect to its anions, it is located on the extreme right of the above series. 

Consider the proper placement of tellurium and iodine in the periodic table, as shown in Figure 1-3. Te has the heavier atomic weight. The chemical properties of tellurium are like those of selenium because both are semi-metallic elements that form compounds like those of sulfur. Iodine resembles bromine because these elements are nonmetallic halogens that form compounds like those of chlorine. Therefore, the order in the table cannot be based solely on atomic weight. 

Tellurium metal, its alloys, minerals or the teUurides may be dissolved in warm concentrated sulfuric acid or cold fuming sulfuric acid to form a red color, the intensity of which is proportional to the tellurium content in the substance. When this red solution is poured into water, black elemental tellurium metal precipitates out of solution. Oxidized tellurium does not respond to this test. 

Toxicity Variable. The hydrides of phosphorus, arsenic, sulfur, selenium, tellurium and boron which are highly toxic, produce local irritation and destroy red blood cells. They are particularly dangerous because of their volatility and ease of entry into the body. The hydrides of the alkali metals, alkaline earths, aluminum, zirconium and titanium react with moisture to evolve hydrogen and leave behind the hydroxide of the metallic element. This hydroxide is usually caustic. See also sodium hydroxide... 

At present there are few examples of isolable, well-characterized sources of tellurolate anions (RTe-).1 Although insertion of elemental tellurium into reactive metal-carbon bonds has been known for many years, the resulting solutions contain a mixture of compounds in addition to the RTe- species of interest.2 Alkali metal phenyltellurolate salts, prepared via metal reduction of diphenyl ditelluride in liquid ammonia, were first isolated by Klar and co-workers.3 More recently Lange and Du Mont reported the synthesis of the bulky aryl tellurolate (THF)3Li[Te(2,4,6-f-Bu3C6H2)],4 and Sladky described the in situ formation of a bulky alkyl tellurolate via reaction of tellurium with LiC(SiMe3)3.5 Acidification of aryltellurolate anions affords thermally sensitive tellurols (RTeH) that are stable only below room temperature.6... 

TELLURIUM. TCAS 13494-80-91. Chemical element, symbol Te, at. no. 52. at. wL 127.60, periodic table group 6, mp 450°C, bp 690°C, density 6.24 g/cm3 (crystalline form at 25°C), 6.00 (amorphous farm at 25°C). Elemental tellurium has a hexagonal crystal structure with trigonal symmetry. Tellurium is a silver-white brittle semi-metal, stable in air, and in boiling H2O, insoluble in HC1, but dissolved by HNOj or aqua regia to form telluric acid. The element is dissolved by NaOH solution and combines with chlorine upon heating to form tellurium tetrachloride. 

On the scale of most other commercial metals, the production of elemental tellurium is relatively limited—approximately j million pounds annually. Commercial tellurium is marketed at a purity of about 99.7%, although much purer forms are obtainable—up to 99.999%. The application of tellurium and tellurium compounds as catalysts is expanding. Small quantities are used in various electronic components, including solar cells, infrared detectors, emitters, and thermoelectric generators. Tellurium also is sometimes used as a dopant for semiconductor... 

Another hazy boundary separates polymeric and metallic substances. We have already noted the case of iodine, which can be described as a molecular solid but which might also be viewed as a two-dimensional polymer having incipient metallic properties. Elemental tellurium, whose chain structure was described earlier in this section, has pronounced metallic properties. Each Te atom is bonded to two others at a distance of 284 pm, and this connectivity leads to a helical chain. However, each Te atom is bonded to four more in other chains, at a distance of 350 pm. These longer Te-Te contacts are apparently responsible for the metallic properties. 

The insertion of elemental tellurium into C — Li or C — Na bonds is a convenient method for the preparation of alkali metal tellurolates. Many organic lithium compounds are commercially available or can be prepared, for instance, by halogen-lithium or hydrogen-lithium exchange. The reactions of the organic lithium compounds with elemental tellurium are performed in inert organic solvents such as diethyl other, tetrahydrofuran, tetrahydrofuran/hexane, or diethyl ether/benzene at temperatures (— 196° to + 20°) compatible with the stability of the organic lithium compound. The applicability of this reaction for the synthesis of aliphatic, aromatic, and heteroaromatic lithium tellurolates is documented in Table 1 (p. 155). 

That the nature of the polytelluride solution plays an important role is also borne out by studies of the chromium-telluride system. If the polytel-lurides are prepared in situ by the reaction of elemental potassium with elemental tellurium in DMF, the products are considerably cleaner and can be obtained in higher yields than when the polytelluride source is a premade potassium salt, such as K2Te2 or K2Te3, It has been suggested that equilibria are occurring in the reaction flask. Pure Te2- and Te2- can be prepared in pure form in liquid ammonia, but there is no evidence for the formation of higher tellurides in the presence of alkali metal counter-... 

A nucleophilic metal anion has been used as a reducing agent to create Zintl ion directly. [PPN]2[Fe2(CO)6(Te2)2] (169) has been synthesized by direct reaction of Na2[Fe(CO)4] with elemental tellurium.115 Although not structurally characterized by X-ray methods, the formulation of 169 is supported by several pieces of experimental evidence. It can react with itself or with the Zintl ions present to produce mixed-metal species. It reacts with iodomethane to yield [Fe2(CO)6(/z-TeMe)2] (170) (Fig. 56),... 

Such representative non-metal elements as boron, silicon, phosphorus, sulfur, arsenic, antimony, selenium and tellurium react with chlorine trifluoride at room temperature or on very slight warming to produce the corresponding fluorides. These reactions are generally vigorous and are accompanied by heat and light [96]. 

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