Carbon reductions with

C, b.p. 907"C, d 713. Transition element occurring as zinc blende, sphalerite (Zn,Fe)S calamine or smithsonite (ZnCO j), willemite (Zo2Si04), franklinite (ZnFe204). Extracted by roasting to ZnO and reduction with carbon. The metal is bluish-white (deformed hep) fairly hard and brittle. Burns... 

Reference to Figure 3.4 shows that the reduction is not feasible at 800 K. but is feasible at 1300 K. However, we must remember that energetic feasibility does not necessarily mean a reaction will go kinetic stability must also be considered. Several metals are indeed extracted by reduction with carbon, but in some cases the reduction is brought about by carbon monoxide formed when air, or air-oxygen mixtures, are blown into the furnace. Carbon monoxide is the most effective reducing agent below about 980 K, and carbon is most effective above this temperature. 

The iodate is a poison potassium iodide, however, is used in foodstuffs. Thus the iodate must be completely removed frequently by a final reduction with carbon. After re-solution in water, further purification is carried out before recrystallization. Iron, barium, carbonate, and hydrogen sulfide are used to effect precipitation of sulfates and heavy metals. 

Chemical Properties. Anhydrous sodium sulfite is stable in dry air at ambient temperatures or at 100°C, but in moist air it undergoes rapid oxidation to sodium sulfate [7757-82-6]. On heating to 600°C, sodium sulfite disproportionates to sodium sulfate and sodium sulfide [1313-82-2]. Above 900°C, the decomposition products are sodium oxide and sulfur dioxide. At 600°C, it forms sodium sulfide upon reduction with carbon (332). 

Tantalum(II) oxide [12035-90-4] TaO, is the only other oxide the existence of which has been confirmed. It can be prepared from Ta20 by reduction with carbon at 1900°C or with H2 at 1100°C. 

Reduction to Metal Powder. The metal powder is obtained from APT by stepwise reduction with carbon or hydrogen. The intermediate products are the yeUow oxide, WO blue oxide, (see Tungsten compounds) and brown oxide, WO2. Because carbon introduces impurities,... 

Viable methods of producing the metals from oxide ores have to siumount two problems. In the first place, reduction with carbon is not possible because of the formation of intractable carbides (p. 299), and even reduction with Na, Ca or Mg is unlikely to remove all the oxygen. In addition, the metals are extremely reactive at high temperatures and, unless prepared in the absence of air, will certainly be contaminated with oxygen and nitrogen. 

Tin and lead are obtained very easily from their ores and have been known since antiquity. Tin occurs chiefly as the mineral cassiterite, SnOz, and is obtained from it by reduction with carbon at 1200°C ... 

Chromium, Cr, is a bright, lustrous, corrosion-resistant metal. Its name, which comes from the Greek word for color, was inspired by its colorful compounds. The metal is obtained from the mineral chromite, FeCr204, by reduction with carbon in an electric arc furnace ... 

FIGURE 16.39 The reduction of iron ore takes place in a blast furnace containing a mixture of the ore with coke and limestone. Different reactions take place in different zones when the blast of air and oxygen is admitted. The ore, an oxide, is reduced to the metal by reduction with carbon monoxide produced in the furnace. 

Roasting arsenic sulfide in air produces the oxide, and the element is obtained from the oxide by reduction with carbon. 

New Jersey A continuous process for extracting zinc from zinc oxide, made by roasting zinc sulfide ore, by reduction with carbon in a vertical retort. First operated by the New Jersey Zinc Company in Palmerton, PA, in 1929, and introduced into the Avonmouth, UK, works of the Imperial Smelting Company in 1934. 

Trail A process for recovering elemental sulfur from sulfur dioxide by reduction with carbon ... 

Preparation. Lead is obtained by roasting PbS to oxide followed by reduction with carbon. 

The oxide can be reduced to metalhc lead by hydrogen, carbon, carbon monoxide and other reducing agents when heated at elevated temperatures. Such reduction with carbon or carbon monoxide is carried out at about 1000°C in a blast furnace to produce lead metal ... 

Reduction with carbon monoxide at high temperatures can form either carbonyl sulfide or sulfur depending on the catalyst used. With cobalt molybdate, COS is the primary product. On the other hand, lanthanum titanate catalyzes the reaction to form sulfur. 

In the process of SiCfr preparation the main raw stock is ferrosilicon, an alloy of iron and silicon, made in shaft electric furnaces. Electrothermal ferrosilicon is produced from quartzite and iron chipping it is reduced with charcoal or coke (petroleum or metallurgical). The process is based on the endothermal reaction of silica reduction with carbon, which takes place at high temperature. 

Conversion of Sulphide to oxide Co, Zn, Pb, Bi and then reduction with carbon... 

Apart from the use of cation exchange with [Au(en)2]3+99,100 (Section 4.3.5), or CVD of Me2Au(acac)94,95 (Section 4.3.4), there are several other methods for introducing gold into the pores of zeolites when the objective is to stabilise the Au1 state after reduction with carbon monoxide. However, with few exceptions, they seem much less satisfactory for forming small metallic particles, as they are usually larger than the pore size, and there is scarcely any evidence for particles being really located inside the pores. 

Note that very little pure vanadium metal is prepared commercially. However, the iron-vanadium alloy obtained by reduction with carbon of a mixture of the two oxides is used in large quantity in the steel... 

Tin and lead have been known since ancient times. Cassiterite, Sn02, was mined in Britain and transported by sea to the Mediterranean area where copper was available. After reducing the Sn02 with charcoal to produce tin, the tin was alloyed with copper to make bronze as early as about 2500 BC. Consequently, tools and weapons made of bronze figured prominently in the period known as the Bronze Age (about 2500 to 1500 BC). At an early time, lead was found as native lead or as galena, PbS, that could be converted to the oxide by roasting the sulfide in air followed by reduction with carbon. As a result, tin and lead are among the elements known for many centuries. Of course, the reason that the metals Sn, Cu, Au,... 

Titanium is relatively abundant in the earth s crust (0.6%). The main ores are ilmenite (FeTi03) and rutile, one of the several crystalline varieties of Ti02. It is not possible to obtain the metal by the common method of reduction with carbon because a very stable carbide is produced moreover, the metal is rather reactive toward oxygen and nitrogen at elevated temperatures. Because the metal has uniquely useful properties, however, expensive methods for its purification are justified. In addition to a proprietary electrolytic method, there is the older Kroll... 

The MoS2 in ores is concentrated by the foam flotation process the concentrate is then converted by roasting into Mo03 which, after purification, is reduced with hydrogen to the metal. Reduction with carbon must be avoided because this yields carbides rather than the metal. 

Less than 15% of the ore is transformed into chromium compounds, principally chromates, dichromates, chromium(VI) oxide, chromium(III) oxide, and so on. Alkaline oxidative roasting of chromite in rotary kilns yields sodium chromate (see equation 1), which is leached out with water and typically converted into sodium dichromate with sulfimc acid (equation 2) or carbon dioxide (equations). Fiuther treatment of sodium dichromate with sulfuric acid yields chromium(VI) oxide ( chromic acid ), while its reduction (with carbon, sulfur, or anuuo-nium salts) produces chromium(III) oxide. Finally, basic chromium(III) salts, for example Cr(0H)S04, which are used as tanning agents for animal hides, also result from reduction of sodium dichromate. Heterogeneous chromium catalysts are used for the polymerization of ethylene. 

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