Alumina Aluminum, reduction

See also Alumina hydroxides classification, 2 422 Aluminum particle size, 10 22-23 Aluminum perchlorate, 18 278 Aluminum phosphide, 2 284 19 58 Aluminum-polyphenylenevinylene-ITO, in photovoltaic devices, 22 221 Aluminum production, 9 639-640 Aluminum recycling, 2 305 21 371-372 economic aspects of, 21 402 remelting, 2 333-334 Aluminum reduction, of ferrovanadium, 25 518... 

The principal method used in producing aluminum metal involves three major steps refining of bauxite by the Bayer process to produce alumina, electrolytic reduction of alumina by the Hall-Heroult process to produce aluminum, and casting of aluminum into ingots (Browning 1969 Dinman 1983 IARC 1984). 

Annual production capacity for aluminum oxide (alumina, calcined, reduction grade) in thousand metric tons was 4,896 (10.8 billion pounds), 5,245 (11.6 billion pounds), 4,980 (11 billion pounds), 4,980 (11 billion pounds), and 5,035 (11.1 billion pounds) in 1988, 1990, 1992, 1994, and 1995, respectively (SRI 1988, 1990, 1992, 1994, 1995). Table 4-2 lists the facilities in each state that manufacture or process aluminum oxide, the intended use, and the range of maximum amounts of aluminum oxide that are stored on site. The data listed in Table 4-2 is derived from the Toxics Release Inventory (TRI96 1998). Only certain types of facilities were required to report (EPA 1995e). Therefore, this is not an exhaustive list. Small quantities of highly purified aluminum oxide are now produced for use in systems that measure doses of ionizing radiation (McKeever et al. 1995). 

As shown in Scheme 6.13, if the catalyst for the reduction is changed from Pt to Pd, the stereochemistry of the reduction is apparently altered. However, once it is recognized that Pd on alumina (aluminum oxide [AI2O3]) causes isomerization—a rearrangement vide infra) from one alkene to another—faster than reduction occurs, the result is explicable. Thus, (Scheme 6.13) 1,2-dimethylcyclohexene... 

In vacuum thermochemical reduction process, aluminum and silicon are suitable reduction agents [5, 6]. Vacuum aluminothermic reduction lithium is from a US patent about aluminum reduction of lithium oxide. Aluminum reduction of spodumene has been reported by Stauffer [7]. Lithium is difficultly reduced if not adding calcium oxide into spodumene. When the mass ratio of calcium oxide and spodumene is 3 2, the maximum productivity was 92.2% under the conditions of 1050 1150"C for 2 hours. Fedorov and Shamrai used aluminum to reduce lithium aluminate, and pointed out that the lithium productivity could reach 95% when the reduction temperature was 1200 C and the system pressure was below 0.0013 Pa [4]. The previous researches were focused on the production of lithium. But the recovery of reduction residue was not investigated. In present work, a novel vacuum aluminofliermic reduction lithium process is developed which used lithium carbonate, alumina and calcium oxide as raw materials. The products were metal lithium and high-whiteness aluminum hydroxide. 

Aluminum. All primary aluminum as of 1995 is produced by molten salt electrolysis, which requires a feed of high purity alumina to the reduction cell. The Bayer process is a chemical purification of the bauxite ore by selective leaching of aluminum according to equation 35. Other oxide constituents of the ore, namely siUca, iron oxide, and titanium oxide remain in the residue, known as red mud. No solution purification is required and pure aluminum hydroxide is obtained by precipitation after reversing reaction 35 through a change in temperature or hydroxide concentration the precipitate is calcined to yield pure alumina. 

No cryolite is actually needed once the smelting process is in operation because cryolite is produced in the reduction cells by neutralizing the Na20 brought into the cell as an impurity in the alumina using aluminum fluoride. 

A fourth ahoy separation technique is fractional crystallization. If shica is co-reduced with alumina, nearly pure shicon and an aluminum shicon eutectic can be obtained by fractional crystallization. Tin can be removed to low levels in aluminum by fractional crystallization and a carbothermic reduction process using tin to ahoy the aluminum produced, fohowed by fractional crystallization and sodium treatment to obtain pure aluminum, has been developed (25). This method looked very promising in the laboratory, but has not been tested on an industrial scale. 

Both the Toth and Alcoa processes provide aluminum chloride for subsequent reduction to aluminum. Pilot-plant tests of these processes have shown difficulties exist in producing aluminum chloride of the purity needed. In the Toth process for the production of aluminum chloride, kaolin [1332-58-7] clay is used as the source of alumina (5). The clay is mixed with sulfur and carbon, and the mixture is ground together, pelletized, and calcined at 700°C. The calcined mixture is chlorinated at 800°C and gaseous aluminum chloride is evolved. The clay used contains considerable amounts of silica, titania, and iron oxides, which chlorinate and must be separated. Silicon tetrachloride and titanium tetrachloride are separated by distillation. Resublimation of aluminum chloride is requited to reduce contamination from iron chloride. 

The predominant process for manufacture of aniline is the catalytic reduction of nitroben2ene [98-95-3] ixh. hydrogen. The reduction is carried out in the vapor phase (50—55) or Hquid phase (56—60). A fixed-bed reactor is commonly used for the vapor-phase process and the reactor is operated under pressure. A number of catalysts have been cited and include copper, copper on siHca, copper oxide, sulfides of nickel, molybdenum, tungsten, and palladium—vanadium on alumina or Htbium—aluminum spinels. Catalysts cited for the Hquid-phase processes include nickel, copper or cobalt supported on a suitable inert carrier, and palladium or platinum or their mixtures supported on carbon. 

Direct ammonolysis involving dehydratioa catalysts is geaerahy ma at higher temperatures (300—500°C) and at about the same pressure as reductive ammonolysis. Many catalysts are active, including aluminas, siUca, titanium dioxide [13463-67-7], and aluminum phosphate [7784-30-7] (41—43). Yields are acceptable (>80%), and coking and nitrile formation are negligible. However, Htfle control is possible over the composition of the mixture of primary and secondary amines that can be obtained. 

High purity 50% ferrosihcon containing <0.1% Al and C is used for production of stainless steel and corded wire for tires, where residual aluminum can cause harm fill alumina-type inclusions. These are also useflil in continuous cast heats, where control of aluminum is necessary. High purity grades of 50 and 75% ferrosihcon containing low levels of aluminum, calcium, and titanium are used for sihcon additions to grain-oriented electrical steels, where low residual aluminum content contributes to the attainment of desired electrical properties, eg, significant reduction of eddy currents. 

Calcium—Silicon. Calcium—silicon and calcium—barium—siUcon are made in the submerged-arc electric furnace by carbon reduction of lime, sihca rock, and barites. Commercial calcium—silicon contains 28—32% calcium, 60—65% siUcon, and 3% iron (max). Barium-bearing alloys contains 16—20% calcium, 9—12% barium, and 53—59% sihcon. Calcium can also be added as an ahoy containing 10—13% calcium, 14—18% barium, 19—21% aluminum, and 38—40% shicon These ahoys are used to deoxidize and degasify steel. They produce complex calcium shicate inclusions that are minimally harm fill to physical properties and prevent the formation of alumina-type inclusions, a principal source of fatigue failure in highly stressed ahoy steels. As a sulfide former, they promote random distribution of sulfides, thereby minimizing chain-type inclusions. In cast iron, they are used as an inoculant. 

Electroplating. Aluminum can be electroplated by the electrolytic reduction of cryoHte, which is trisodium aluminum hexafluoride [13775-53-6] Na AlE, containing alumina. Brass (see COPPERALLOYS) can be electroplated from aqueous cyanide solutions which contain cyano complexes of zinc(II) and copper(I). The soft CN stabilizes the copper as copper(I) and the two cyano complexes have comparable potentials. Without CN the potentials of aqueous zinc(II) and copper(I), as weU as those of zinc(II) and copper(II), are over one volt apart thus only the copper plates out. Careful control of concentration and pH also enables brass to be deposited from solutions of citrate and tartrate. The noble metals are often plated from solutions in which coordination compounds help provide fine, even deposits (see Electroplating). 

An enamine was obtained in the synthesis of coronaridine (648) by aluminum hydride reduction of a bridged lactam, followed by dehydration on alumina. Additional examples of enamine formation by reduction of enamides (649) and thioenamides (650) were reported. 

The electrolytic processing of concentrated ore to form the metal depends on the specific chemical properties of the metallic compound. To produce aluminum about 2 to 6 percent of purified aluminum oxide is dissolved in ciyolite (sodium alumi-no-fliioride, Na AlF ) at about 960°C. The reduction of the alumina occurs at a carbon (graphite) anode ... 

A certain amount of iron oxide is present in the alumina slag and a certain amount of aluminum is present in the as-reduced iron. Assuming Raoult s law, an aluminum content of 1 wt-% in iron will correspond to A 0.02. The value of aFeG is then 6 10 4. Even a trace of aluminum dissolved in liquid iron results in a practically complete reduction of iron oxide from the slag phase. The assumption that the product phases are pure iron metal and alumina slag thus holds. 

The reactor used for the aluminothermic reduction of niobium pentoxide is shown schematically in Figure 4.17 (A). It is a steel pipe, lined on the inside with alumina and provided with a pipe cap. The charge, consisting of stoichiometric amounts of niobium pentoxide and aluminum powder, is blended and loaded in the lined pipe, and covered with alumina. The cap is closed and the reaction initiated by placing the loaded bomb in a gas-fired furnace, preheated to 800 °C, and by raising the temperature of the furnace to 1100 °C. 

The excess aluminum in the charge compensates for the loss of aluminum due to nonreductive air oxidation, and also provides aluminum for alloying with the niobium metal produced in the reduction. As mentioned earlier, the liquidus temperatures of niobium-aluminum alloys are lower than the melting point of niobium. The melting of this alloy and the alumina slag is achieved even with the reduced amount of heat available from the reaction implemented without preheating in the open reactor. 

The first production of aluminum was by the chemical reduction of aluminum chloride with sodium. The electrolytic process, based on the fused salt electrolysis of alumina dissolved in cryolite, was independently developed in 1886 by C. M. Hall in America and P. L. Heroult in France. Soon afterwards a chemical process for producing pure alumina from bauxite, the commercial source of aluminum, was developed by Bayer and this led to the commercial production of aluminum by a combination of the Bayer and the Hall-Heroult processes. At present this is the main method which supplies all the world s needs in primary aluminum. However, a few other processes also have been developed for the production of the metal. On account of problems still waiting to be solved none of these alternative methods has seen commercial exploitation. 

The Hall-Heroult process is a prodigious consumer of electrical energy. The energy required to produce 1 ton of aluminum from ore is more than twice that required to produce 1 ton of copper and ten times that for 1 ton of steel. More than 75% of this energy is consumed in the reduction of alumina to aluminum metal. The reasons for this high energy consumption have been presented in Table 6.18. The theoretical energy requirement for... 

---