Aluminum purification

Purification. Extraction from aluminum or 2inc ores produces cmde galHum metal or concentrates. These concentrates are transformed to sodium gallate, galHum chloride, or galHum sulfate solutions which are purified, then electroly2ed. GalHum is deposited as a Hquid. 

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. 

Sodium aluminate is used in water purification, in the paper industry, for the after treatment of Ti02 pigment, and in the manufacture of aluminum containing catalysts and zeoHte. Worldwide markets are in the range of 125,000 t/yr (19). 

Aluminum sulfate is a starting material in the manufacture of many other aluminum compounds. Aluminum sulfate from clay could potentially provide local sourcing of raw materials for aluminum production. Processes have been studied (24) and the relative economics of using clay versus bauxite have been reviewed (25). It is, however, difficult to remove impurities economically by precipitation, and purification of aluminum sulfate by crystallization is not practiced commercially because the resulting crystals are soft, microscopic, and difficult to wash effectively on a production scale (26—28). 

Refining. In order to produce silicon that meets the requirements of the chemical, ie, siUcones, and primary aluminum markets, the siUcon produced in the arc furnace requires further purification. The quaUty of siUcon for the chemical siUcones industry is critical with respect to the levels of aluminum and calcium present, and the primary aluminum grade of siUcon requires low levels of calcium, iron, and phosphoms. The impurity requirements for the secondary aluminum market are not as stringent, so long as the siUcon content is >98.5%. 

Examination of the metallic product (regulus) of such aluminothermically produced vanadium metal reveals the presence of oxide phases in the metal matrix. This suggests that there is a decreasing solubiHty for aluminum and oxygen below the melting point. To date, no purification processes have been developed that take advantage of the purification potential of this phenomenon. 

The vanadium alloy is purified and consoHdated by one of two procedures, as shown in the flow diagram of the entire aluminothermic reduction process presented in Figure 1. In one procedure, the brittle alloy is cmshed and heated in a vacuum at 1790°C to sublime most of the aluminum, oxygen, and other impurities. The aluminum faciHtates removal of the oxygen, which is the feature that makes this process superior to the calcium process. Further purification and consoHdation of the metal is accompHshed by electron-beam melting of pressed compacts of the vanadium sponge. 

Purification actually starts with the precipitation of the hydrous oxides of iron, alumina, siUca, and tin which carry along arsenic, antimony, and, to some extent, germanium. Lead and silver sulfates coprecipitate but lead is reintroduced into the electrolyte by anode corrosion, as is aluminum from the cathodes and copper by bus-bar corrosion. 

Preparation. The simplest method of preparation is a combination of the elements at a suitable temperature, usually ia the range of 1100—2000°C. On a commercial scale, borides are prepared by the reduction of mixtures of metallic and boron oxides usiag aluminum, magnesium, carbon, boron, or boron carbide, followed by purification. Borides can also be synthesized by vapor-phase reaction or electrolysis. 

Purification. Alumina, AI2O3, is produced by the Bayer process (1,9) (see Aluminum COMPOUNDS) which involves digestion foUowed by precipitation and calcination. High purity magnesia is extracted from natural brines and seawater by precipitation and calcination (1,9). 

Compact brazed aluminum plate-fin heat exchangers can be used in most cryogenic hydrogen purification apphcations. The use of these relatively low cost heat exchangers, combined with low separation energy requirements, results in a highly economical process for hydrogen purification. 

Hydroquinone may also be used in place of 4-chloroplienol. In this case an aluminum chloride—sodium chloride melt is usually employed. However, the yield is not satisfactory (43). It has also been reported that the reaction of hydroquinone with substantially stoichiometric phthaUc acid dichloride in the presence of anhydrous aluminum chloride in moderately polar solvents, such as nitrobenzene at around 100°C gives quinizarin (44). The reported yield is 65% after purification by crystallization from toluene. 

At the alumina plant, the bauxite ore is further crushed to the correct particle size for efficient extraction of the alumina through digestion by hot sodium hydroxide liquor. After removal of "red mud" (the insoluble part of the bauxite) and fine solids from the process liquor, aluminum trihydrate crystals are precipitated and calcined in rotary kilns or fluidized bed calciners to produce alumina (AljOj). Some alumina processes include a liquor purification step. 

A mixture of 50 g of betamethasone, 50 cc of dimethylformamide, 50 cc of methyl orthobenzoate and 1.5 g of p-toluenesulfonicacid Is heated for 24 hours on oil bath at 105°C while a slow stream of nitrogen is passed through the mixture and the methanol produced as a byproduct of the reaction is distilled off. After addition of 2 cc of pyridine to neutralize the acid catalyst the solvent and the excess of methyl orthobenzoate are almost completely eliminated under vacuum at moderate temperature. The residue Is chromatographed on a column of 1,500 g of neutral aluminum oxide. By elution with ether-petroleum ether 30 g of a crystalline mixture are obtained consisting of the epimeric mixture of 170 ,21 -methyl orthobenzoates. This mixture is dissolved without further purification, in 600 cc of methanol and 240 cc of methanol and 240 cc of aqueous 2 N oxalic acid are added to the solution. The reaction mixture is heated at 40°-50°C on water bath, then concentrated under vacuum. The residue, crystallized from acetone-ether, gives betamethasone 17-benzoate, MP 225°-231°C. 

The procedure employs a readily available starting material and produces the pure trans isomer in high yield. The method described is an improvement on that used by Eliel and Rerick2 in that it is not necessary to use a clear solution of lithium aluminum hydride in ether for the preparation of the mixed hydride. It is not necessary to know the precise amount of lithium aluminum hydride used so long as a slight excess is present. The excess hydride is destroyed by adding /-butanol the excess /-butanol has no effect on the subsequent equilibration and purification. The equilibration of the 4 / butylcyclohexanol is effected by adding a small amount of 4-/-butylcyclohexanone. 

The products of this electrolysis have a variety of uses. Chlorine is used to purify drinking water large quantities of it are consumed in making plastics such as polyvinyl chloride (PVC). Hydrogen, prepared in this and many other industrial processes, is used chiefly in the synthesis of ammonia (Chapter 12). Sodium hydroxide (lye), obtained on evaporation of the electrolyte, is used in processing pulp and paper, in the purification of aluminum ore, in the manufacture of glass and textiles, and for many other purposes. 

To an ice-cold solution of the aldehydo sugar in CH,OH (ca. 25 mL per g) are added 3 equiv of nitromethane (or nitrocthane), followed by 2.9 equiv of sodium methoxide. After stirring for 2 h 45 min, the medium is neutralized by the addition of acidic Dowex 50, then filtered. Removal of the solvent by distillation and purification by chromatography on silica gel (Ei,0/hcxane) or on aluminum oxide (Et20) furnishes the product yield 85-99%. 

A -( 1-Chloro- or bromoalkyl)amides are generally moisture-sensitive, unstable compounds, which are often directly used without further purification. Standard Lewis acids such as boron trifluoride-diethyl ether, aluminum(lll) chloride, zinc(II) chloride, tin(IV) chloride and titani-um(IV) chloride are used to generate the /V-acyliminium ion, although sometimes a catalyst is not necessary. 

The dinitrophenylhydrazones were separated from the reaction mixture by thin-layer chromatography (silica gel G developed with benzene) and further purified by thin-layer chromatography on aluminum oxide G (petroleum ether-diethyl ether (96 to 4), silica gel G (chloroform), and silica gel G (diethyl ether)). In all cases, the specific activities of the dinitrophenylhydrazones remained constant over the course of the last two purifications. 

It should be emphasized that Si-H containing compounds should be carefully handled during purification so as to avoid hydrolysis of Si-H bonds. An effective method to suppress hydrolysis of Si-H bonds is to reduce the polarity of the medium by the addition of a large amount of n-hexane before the aluminum compound is removed by washing with dilute cold HC1 solution. 

Lead dioxide as oxidizing agent for conversion of 2-hydroxy-3-methyl-benzoic add to 2-hydroxyiso-phthalic acid, 40, 48 Lithium aluminum hydride, in purification of 1,2-dimethoxyethane, 41, 97... 

Analysis and purification of the product solution is best accomplished by gas chromatography. The submitters used a 500 cm. by 0.6 cm. aluminum or polyethylene column packed with 21% oxydipropionitrile on Chromosorb P with column, injector and detector operated at 25° and a flow rate of 50 ml./minute. Under these conditions the retention times of bicyclopentene and cyclopentadiene were 3 and 5 minutes, respectively, beyond that of the coinjected air. Since bioyclo-pentene is extremely labile with respect to acid catalysis any contact with water, hydroxylic solvents, and nonprotic acids should be avoided (Note 11). Bicyclopentene stored at —78° in anhydrous tetrahydro-furan is stable indefinitely. 

Sodium aluminate, NaAl(OH)4, is used along with aluminum sulfate in water purification. When mixed with aluminate ions, the acidic hydrated Al3+ cation from the aluminum sulfate produces aluminum hydroxide ... 

FIGURE 14.26 Aluminum hydroxide, Al(OH) forms as a white, fluffy precipitate. The fluffy form of the solid captures impurities and is used in the purification of water. 

C03-0152. Aluminum sulfate is used in the manufacture of paper and in the water purification industry. In the solid state, aluminum sulfate is a hydrate. The formula is AI2 (804)3 18 H2 O. (a) How many grams of sulfiar are there in 0.570 moles of solid aluminum sulfate (b) How many water molecules are there in a 5.1-g sample of solid aluminum sulfate (c) How many moles of sulfate ions are there in a sample of solid aluminum sulfate that contains 12.5 moles of oxygen atoms (d) An aqueous solution of aluminum sulfate contains 1.25% by mass aluminum and has a density of 1.05 g/mL. What is the molarity of aluminum ions in the solution ... 

Iron has been the dominant structural material of modem times, and despite the growth in importance of aluminum and plastics, iron still ranks first in total use. Worldwide production of steel (iron strengthened by additives) is on the order of 700 million tons per year. The most important iron ores are two oxides, hematite (Fc2 O3) and magnetite (Fc3 O4). The production of iron from its ores involves several chemical processes that take place in a blast furnace. As shown in Figure 20-22. this is an enormous chemical reactor where heating, reduction, and purification all occur together. 

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