how is aluminium extracted from bauxite ore

how is aluminium extracted from bauxite ore

Extraction Process of Aluminium from Bauxite Ore

Aluminum is the most abundant metal in the earths crust and is a constituent of many minerals. However, the material which is highest in aluminum and most free from objectionable impurities is bauxite which, therefore, is practically the only source of the metal under present processes.

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Bauxite is the general name given to the hydrated oxides of aluminum. It contains varying amounts of combined water and several impurities of which ferric oxide and silica are usually predominant. It is essential that the Al2O3 be obtained substantially free from these impurities as otherwise the iron oxide and silica would be reduced and contaminate the metallic aluminum produced in the Hall Process.

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The separation of the alumina from the impurities in the bauxite ore is usually accomplished by the Bayer Process. In this process the ground bauxite is leached with caustic soda to produce soluble sodium aluminate , leaving the impurities in the insoluble residue. The aluminate solution is then decomposed producing Al3 which is calcined to produce Al2O3. In the standard Bayer Process for refining bauxite to produce alumina, the dissolution of the alumina in the ore to form sodium aluminate is accomplished in autoclaves under high pressures varying from 70 to 200 pounds per square inch. However, some lateritic bauxite ores are readily soluble in caustic, making it possible for them to be leached, or digested, at atmospheric pressure.

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This study deals with the treatment of one such lateritic bauxite ore. Batch laboratory tests showed that a high alumina extraction in caustic could be accomplished at a coarse grind, thus promising low grinding costs, and, of greater importance, a coarse sand residue which could be washed more efficiently, thus keeping soluble loss to only a trace. The optimum grind was found to be minus 3/16 with 51% plus 32 mesh. However, at this coarse grind and at the desirable pulp density for digestion of approximately 23% solids, the heavy specific gravity solids had a settling rate as high as 75 feet per minute. The problem resolved itself to finding some type of continuous mixer or agitator which would keep the coarse, fast settling solids in homogeneous suspension during the digestion operation so that all of the bauxite particles would be attacked by the caustic sodium aluminate liquor. In this way it would be possible to capitalize on the important advantages of the coarse grind. The flowsheet in this study illustrates only the following two steps in the modified Bayer Process: In this study the minus 1.5 bauxite ore is ground to minus 3/16 in a Steel Head Rod Mill operating in open circuit. The ore is ground wet with hot sodium aluminate liquor at a temperature of 110°C. The rod mill is equipped with water cooled bearings because of this high temperature.

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The rod mill discharges to a Agitator equipped with a turbine type propeller. The agitator acts as a mixing tank to mix the rod mill discharge with caustic soda and sodium aluminate liquor ead of the digestion circuit. The slurry is pumped from this agitator with a Sand Pump to the digesters for the dissolution of the alumina content of the ore. The slurry from each of these agitators is pumped to a series of nine 22 ft. diameter x 20 ft. deep Digestion Agitators, each of which is equipped with a 96 diameter turbine type propeller consuming 70 HP. Eight Agitators in each series are operational, with the ninth employed as a stand by. Each series of eight agitators handles 19,800 gallons per minute of slurry, and the reaction time is three hours.

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The digestion process is accomplished in a series of several Agitators to prevent short circuiting. As the digestion process continues and the alumina is dissolved, the specific gravity of the solids is actually higher at the discharge point than it is when introduced to the circuit. The bauxite sodium aluminate slurry is maintained at a temperature of 107°C by means of steam coils around the inside periphery of the covered concrete tanks. The interconnecting piping between the agitators is arranged so that any one agitator acts as a standby and can be by passed for maintenance.

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The overflow of the first spiral classifier joins the hydro classifier overflow, and these products flow to the fine red mud washing thickeners mentioned above. The sodium aluminate liquor which overflows the primary thickener is clarified by filtering and the filtrate is decomposed to aluminum hydroxide which is calcined to produce the final alumina product.

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Results at this plant are excellent, enabling this plant to realize a high alumina extraction with a minimum soluble loss.

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Extraction of Aluminium Hall Heroults ...

Bauxite is the name given to aluminium ore. To generate aluminium oxide, bauxite is purified, a white powder form which aluminium can be extracted. Aluminium oxide has a very high melting point of more than 2000 ° C so melting it would be costly. Aluminium oxide in water does not dissolve, but in molten cryolite, it dissolves.

3 minHow Aluminium is extracted from its ore?Bauxite is also aluminium ore. To obtain aluminium oxide, bauxite is purified, a white powder form in which aluminium can be extracted. Electrolysi...Why is Aluminium extracted from alumina?Aluminium is more reactive than carbon and has more oxygen affinity, so aluminium can not be reduced by burning, but is removed by electrolytic red...What is aluminium used for?Aluminium is a lightweight, silver white metal. Its gentle, malevolent. In a wide variety of products, aluminium is used from bottles, foils, kitc...What are the properties of Aluminium?Pure aluminium has high electrical conductivity and is flexible, ductile, corrosion resistant. Aluminium is being used in an ever increasing number...What are the types of Aluminium?There are two main classifications, casting alloys and wrought alloys, both further subdivided into the heat treatable and non heat treatable categ...Why is Aluminium ore purified?Bauxite is also aluminium ore. To obtain aluminium oxide, bauxite is purified, a white powder form which aluminium can be removed. It is an alumini...Can Aluminium be extracted by smelting?The primary use of Smelting is to make metal from the ore. It includes mining of iron from iron ore, and mining of copper and other base metals fro...
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