Bauxite, aluminum from

Most metals will precipitate as the hydroxide in the presence of concentrated NaOH. Metals forming amphoteric hydroxides, however, remain soluble in concentrated NaOH due to the formation of higher-order hydroxo-complexes. For example, Zn and AP will not precipitate in concentrated NaOH due to the formation of Zn(OH)3 and Al(OH)4. The solubility of AP in concentrated NaOH is used to isolate aluminum from impure bauxite, an ore of AI2O3. The ore is powdered and placed in a solution of concentrated NaOH where the AI2O3 dissolves to form A1(0H)4T Other oxides that may be present in the ore, such as Fe203 and Si02, remain insoluble. After filtering, the filtrate is acidified to recover the aluminum as a precipitate of Al(OH)3. 

Starch is a polysaccharide found in many plant species. Com and potatoes are two common sources of industrial starch. The composition of starch varies somewhat in terms of the amount of branching of the polymer chains (11). Its principal use as a flocculant is in the Bayer process for extracting aluminum from bauxite ore. The digestion of bauxite in sodium hydroxide solution produces a suspension of finely divided iron minerals and siUcates, called red mud, in a highly alkaline Hquor. Starch is used to settle the red mud so that relatively pure alumina can be produced from the clarified Hquor. It has been largely replaced by acryHc acid and acrylamide-based (11,12) polymers, although a number of plants stiH add some starch in addition to synthetic polymers to reduce the level of residual suspended soHds in the Hquor. Starch [9005-25-8] can be modified with various reagents to produce semisynthetic polymers. The principal one of these is cationic starch, which is used as a retention aid in paper production as a component of a dual system (13,14) or a microparticle system (15). 

Chemical Raw Material. In addition to use as a catalyst raw material, clays are used or have been extensively studied as chemical raw material. For example, kaolin has been investigated as a raw material for aluminum metal production. Kaolin has a 38 to 40% alumina content and is available in the United States in large quantities whereas the higher alumina bauxite reserves are very limited. The Bureau of Mines has actively carried out research in the aluminum from ka olin area for many years. Activity increases whenever imports of bauxite are threatened by war or other trade intermptions (1,22,23). 

In contrast, aluminum (abundance = 7.5%), despite its usefulness, was little more than a chemical curiosity until about a century ago. It occurs in combined form in clays and rocks, from which it cannot be extracted. In 1886 two young chemists, Charles Hall in the United States and Paul Herroult in France, independently worked out a process for extracting aluminum from a relatively rare ore, bauxite. That process is still used today to produce the element. By an odd coincidence, Hall and Herroult were born in the same year (1863) and died in the same year (1914). 

The process for obtaining aluminum from bauxite was worked out in 1886 by Charles Hall (1863-1914), just after he graduated from Oberlin College. The problem that Hall faced was to find a way to electrolyze Al203 at a temperature below its melting point of 2000°C. His general approach was to look for ionic compounds in which Al203 would dissolve at a reasonable temperature. After several unsuccessful attempts, Hall found that cryolite was the... 

This process has been tried out on a pilot plant scale mainly as a means of producing pure aluminum from an impure aluminum-iron (20-45%)-silicon (2-20%) alloy, obtained by the carbothermic reduction of bauxite in an electric furnace. 

InTox A process for destroying toxic wastes in aqueous solution by oxidation with oxygen at high temperatures and pressures in a pipe reactor. No catalyst is required. The reactions take place at approximately 300°C and 120 atm. Developed by InTox Corporation, UK, based on a process for extracting aluminum from bauxite developed by Lurgi in the 1960s. See also Zimpro. 

Pedersen A process for extracting aluminum from bauxite, which also yields metallic iron. The ore is first smelted in an electric furnace with limestone, iron ore, and coke at 1,350 to 1,400°C to produce a calcium aluminate slag and metallic iron. Aluminium is leached from the slag by sodium carbonate solution, and alumina is then precipitated from the leachate by carbon dioxide. The process requires cheap electricity and a market for the iron. It was invented by H. Pedersen in 1924 and operated at Hoy anger, Norway, from 1928 until the mid-1960s. British Patent 232,930. 

Peniakoff A process for extracting aluminum from bauxite or other aluminous ores. The ore is roasted with coke and sodium sulfate in a rotary kiln at 1,200 to 1,400°C this converts the aluminum to sodium aluminate, which is leached out with dilute sodium hydroxide solution. The basic reactions are ... 

VAW Lurgi [Vereinigte Aluminiumwerke] An energy-efficient process for extracting aluminum from bauxite. Extraction is done in a pipe reactor, and the aluminum hydroxide is converted to the oxide in a fluidized bed. 

Bauxite is the most abundant ore of aluminum. The first step in extracting aluminum from bauxite is called the Bayer process. The Bayer process involves a fractional precipitation of impurities, including iron(lll) oxide and titanium dioxide. Search the Internet to find the history of the Bayer process and learn how it works. Present your findings as a poster. To start your search, go to the web site above and click on Web Links. 

One of the most important electrolytic processes is the extraction of aluminum from an ore called bauxite. This ore is mainly composed of hydrated aluminum oxide, AI2O3 XH2O. (The x in the formula indicates that the number of water molecules per formula unit is variable.) In industry, the scale of production of metals is huge. The electrolytic production of aluminum is over two million tonnes per year in Canada alone. As you know from Faraday s law, the amount of a metal produced by electrolysis is directly proportional to the quantity of electricity used. Therefore, the industrial extraction of aluminum and other metals by electrolysis requires vast quantities of electricity. The availability and cost of electricity greatly influence the location of industrial plants. 

Aluminum scrap is one of the salvaged and recycled metals that is less expensive to reuse than it is to extract the metal from its ore. In other words, it takes much less electricity to melt scrap aluminum than it does to extract aluminum from bauxite. 

Electrolysis is used to purify metals from metal ores. An example is aluminum, the third most abundant element in Earths crust. Aluminum occurs naturally bonded to oxygen in an ore called bauxite. Aluminum metal wasn t known until about 1827, when it was prepared by reacting bauxite with hydrochloric acid. This reaction gave the aluminum ion, Al3 ", which was reduced to aluminum metal with sodium metal acting as the reducing agent ... 

Note that the carbon electrode takes part in the reaction. From the reaction stoichiometry, we can calculate that a current of 1 A must flow for 80 h to produce 1 mol A1 (27 g of aluminum, about enough for two soft-drink cans). The very high energy consumption can be greatly reduced by recycling, which requires less than 5% of the electricity needed to extract aluminum from bauxite (Box 14.1). Note also that the production of 1 tonne of aluminum is accompanied by the release of more than 1 tonne of carbon dioxide into the atmosphere. 

The dissolution of hydrated alumina in concentrated aqueous solutions of sodium hydroxide at elevated temperatures and pressures is the basic step in the extraction of aluminum from bauxite via the Bayer process.34 This dissolution reaction is described by the equation... 

Fluorine occurs in nature in the form of the minerals fluorite, CaF2, cryolite, Na3AlF6, and fluoroapatite, Ca5(P04)3F, and one commercial source of natural cryolite is Greenland. Both of the other minerals are widespread in nature, although the major use of fluoroapatite is in the production of fertilizers, not as a primary source of fluorine. Extensive fluorite deposits are found in Southeastern Illinois and Northwestern Kentucky. From the standpoint of fluorine utilization, both cryolite and fluorite are extremely important minerals. Cryolite is used as the electrolyte in the electrochemical production of aluminum from bauxite, and fluorite is used as a flux in making steel. Today, most of the cryolite used is synthetic rather than the naturally occurring mineral. 

Finally, corundum is indirectly a major source of aluminum metal. The ore of aluminum, called bauxite, is a mixture of several minerals containing aluminum together with oxygen and hydrogen. The first step in releasing the aluminum from the other elements is to convert the bauxite to corundum. 

Good descriptions of the production of aluminum can be found in the literature (Grjotheim etal. [7], Grjotheim and Welch [8], Grjotheim and Kvande [9], Burkin [10], and Peterson and Miller [11]). Referring to Fig. 2 [12], the first step in the production of aluminum from its ore ( bauxite ) is the selective leaching of the aluminum content (present as oxides/hy dr oxides of aluminum) into hot concentrated NaOH solution to form sodium aluminate in solution. After solution purification, very pure aluminum hydroxide is precipitated from the cooled, diluted solution by addition of seed particles to nucleate the precipitation. After solid-liquid separation the alumina is dried and calcined. These operations are the heart of the Bayer process and the alumina produced is shipped to a smelter where the alumina, dissolved in a molten salt electrolyte, is electrolyt-ically reduced to liquid aluminum in Hall- Heroult cells. This liquid aluminum,... 

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