Extraction of Aluminium
The extraction of aluminium involves the electrolysis of aluminium oxide dissolved in molten cryolite. This process takes place in a large cell called an electrolytic cell, where a direct current is passed through the molten mixture to separate the aluminium from the oxygen. The extracted aluminium is then used in various industrial applications due to its lightweight and corrosion-resistant properties.
5 Key excerpts on "Extraction of Aluminium"
eBook - ePub- David Doran, Bob Cather, David Doran, Bob Cather(Authors)
- 2013(Publication Date)
- Routledge(Publisher)
...About 85% of bauxite mined is used to produce the alumina, aluminium oxide, using the Bayer chemical process from which is produced aluminium using the Hall-Héroult electrolytic process. In 2011 more than 220 million tonnes (Mt) of bauxite was mined. 1 The major locations of extraction are Australia (67 Mt), China (46 Mt), Brazil (28 Mt), India (20 Mt), Guinea (18 Mt), Jamaica (10 Mt), Russia (6 Mt), Kazakhstan (5 Mt) and Suriname (5 Mt). In 2011 the world primary aluminium (aluminium tapped from electrolytic cells or pots during the electrolytic reduction of metallurgical aluminium oxide) production 2 was estimated at 25.6 Mt, with north America contributing 5.0 Mt, east and central Europe 4.3 Mt, west Europe 4.0 Mt, GAC/Gulf region 3.5 Mt, Asia 2.5 Mt, Oceania 2.3 Mt, South America 2.2 Mt and Africa 1.9 Mt. Aluminium primary production in the UK in 2010 was 0.186 Mt. 1, 3 Figure 2.3 Bauxite mining in progress Figure 2.4 Bauxite mine shown in Figure 2.3 following reinstatement 2.4 Manufacturing aluminium The refining of the mined bauxite ore is completed in two stages: first the Bayer process, which obtains alumina from the bauxite ore, and second, the Hall-Héroult process that turns the alumina into aluminium. Four tonnes of bauxite makes 2 t of alumina, which makes 1 t of aluminium. 4, 5 2.4.1 The Bayer process 4 Bauxite, mined in the form of granules, is digested, depending on the property of the ore, at 140 to 240°C and pressures up to 3.5 MPa, with caustic soda to dissolve the aluminium, leaving the iron, silicon and titanium compounds undissolved. The residues are filtered and washed to leave liquor that contains only aluminium in the caustic solution. The aluminium is precipitated out as a hydrate, filtered, washed and calcined to produce the alumina, aluminium oxide. The excess caustic is removed from the residues and reused...
eBook - ePubAlumina Ceramics
Biomedical and Clinical Applications
- Andrew J. Ruys(Author)
- 2018(Publication Date)
- Woodhead Publishing(Publisher)
...3 Refining of alumina: The Bayer process Abstract This chapter is primarily focussed on bauxite refining by the Bayer process, which is used for large-scale mass production of alumina that currently takes place on the scale of over 100 million tonnes per year worldwide, over 85% of which is used to service the aluminum industry, and the remaining 15%, in the order of 15 million tonnes a year, services the alumina industries: alumina ceramics, refractories, alumina cement, abrasives, and chemical uses of alumina. The final section of this chapter (Section 3.8) will look at alternatives to the Bayer process for mass production of alumina. This chapter will overview the Bayer process in detail, and also look at the key alternatives to the Bayer process in terms of their economics and technological platform. Keywords Bayer process; Alumina ceramics; Sodium hydroxide; Reactive silica; Gibbsite precipitation; Sodium oxalate; Gibbsite calcination 3.1 Overview of the Bayer process for refining bauxite into alumina The Bayer process is so industrially important to both the alumina and the aluminum industries, that it will receive a detailed focus in this chapter, given that it is the foundation upon which both the alumina and the aluminum industries are built. As discussed in Chapter 1, the Bayer process was invented by Austrian chemist Karl Josef Bayer in 1887, and he patented it in two separate patents, one filed in 1887 and granted in 1888 [ 15 ] and one filed in 1892 and granted in 1894 [ 16 ]. The Bayer process has since become the cornerstone of alumina and aluminum production worldwide...
eBook - ePub- W. Bolton, R.A. Higgins(Authors)
- 2014(Publication Date)
- Routledge(Publisher)
...Unfortunately, this cannot be reduced to the metal by heating it with coke (as in the case of iron ore), because aluminium atoms are, so to speak, too firmly combined with oxygen atoms to be detached by carbon. For this reason, an expensive electrolytic process must be used to decompose the bauxite and release aluminium. Since each kilogram of aluminium requires about 91 mJ of electrical energy, smelting plant must be located near to sources of cheap hydroelectric power, often at great distances from the ore supply, and from the subsequent markets. Consequently, most aluminium is produced in the USA, and in Canada, and Norway. Flydroelectric power in the Western Flighlands enables some aluminium to be smelted in Scotland, but the bulk of aluminium used in the UK is imported. Crude pig iron can be purified (turned into steel) by blowing oxygen over it, to burn out the impurities (see Section 11.2), but this would not be possible in the case of aluminium, since the metal would burn away first, and leave us with the impurities. Instead, the crude bauxite ore is first purified by means of a chemical process, and the pure aluminium oxide is then decomposed by electrolysis. Since aluminium oxide has a very high melting-point, it is mixed with another aluminium mineral, cryolite, to form an electrolyte which will melt at a lower temperature. The furnace used consists of a 'tank' some 2.5 m long to contain the molten electrolyte. It is lined with carbon and this constitutes the cathode of the electrolytic cell. Carbon rods dipping into the electrolyte form the anode. In the molten electrolyte, the aluminium oxide (Al 2 O 3) dissociates into ions: Al 2 O 3 → 2Al +++ + 3O -- The Al ++ ions are attracted to the cathode, where they receive electrons to become atoms. This aluminium collects at the base of the 'tank' and is tapped off at intervals...
eBook - ePub- Christian Vargel(Author)
- 2020(Publication Date)
- Elsevier Science(Publisher)
...In fact, bauxite compositions vary depending on the source of ore but they usually contain aluminium hydroxides such as gibbsite Al(OH) 3, boehmite γ-AlO(OH) and diaspore α-AlO(OH), the rest being composed essentially of iron oxides and hydroxides, mainly haematite, α-Fe 2 O 3 and goethite FeO(OH) (the source of its red colour), and the aluminosilicate clay mineral kaolinite, Al 2 Si 2 O 5 (OH) 4. Even though it is the most abundant metal in the Earth's crust (83,000 ppm) and the third most abundant element after oxygen and silicon, aluminium did not become an industrial metal before the end of the 19th century. Alumina is one of the most stable of all oxides, with an enthalpy of formation, ΔG, of − 1,582 kJ·mol − 1 (the enthalpy of iron oxide is − 1,015 kJ·mol − 1). It is hence very difficult to reduce alumina. The discovery of metallic aluminium is attributed to Sir Humphrey Davy (1778–1829). He referred to it using the term ‘aluminium’ in 1809. By electrolysis of molten aluminium salts, he obtained an alloy of aluminium with iron, because he had used an iron cathode [3]. The chemist Hans Christian Oersted (1777–1851) and later Friedrich Wöhler (1800–1882) chose to reduce aluminium chloride with potassium. The chloride had been prepared by chlorination of bauxite in the presence of carbon. It was Wöhler who, in 1827, succeeded in producing a sufficiently pure metal to determine some of its properties, most notably its low density. There were initially two routes for the industrial production of aluminium: • By a chemical method (1856–1889); • Followed by the electrochemical process invented in 1886 and still in use today. 1.1. Chemically produced aluminium In 1854, Henri Sainte-Claire Deville (1817–1881) improved Wöhler's process. He replaced potassium with sodium for two reasons: the reduction of 1 mol of Al uses 3 mol of sodium, totalling 60 g, instead of 3 mol of potassium amounting to 117 g. At that time, sodium was less expensive than potassium...
eBook - ePubExtractive Metallurgy 2
Metallurgical Reaction Processes
- Alain Vignes(Author)
- 2013(Publication Date)
- Wiley-ISTE(Publisher)
...Chapter 2 Electrometallurgical Extraction Processes 2.1. Overview of electrometallurgical processes Electrometallurgy deals with the conversion of metallic salts, oxides or sulfides into metals (electrowinning) or with purification of the metals (electrorefining) by electrolytic processes, i.e. processes where the chemical energy required by the chemical reactions is supplied by electrical energy, involving passage of an electric current through an electrolyte that conducts current between two electrodes There are two main electrolysis processes: – aqueous salt electrolysis: electrowinning of metals (Cu, Zn, Ni, Co, Cd and Cr) from their salts and electrorefining of impure metals (copper, nickel, lead and tin); – fused salt electrolysis: electrowinning of magnesium from MgCl 2, of aluminum from alumina. The extraction of metals from their salts or oxides by electrolysis requires the electrolyte to be an ionic conductor. An electrolyte possessing electronic conductibility leads to a decrease in current efficiency. Therefore, the electrolyte can only be a salt in an aqueous solution or a mixture of molten salts or oxides. The extraction of metals by electrolysis of salts (chlorides or sulfates) in an aqueous solution is limited by the discharge of H+ ions (see section 2.3.3). Metals whose electrode potential is more negative than the hydrogen overvoltage can only be obtained by electrolysis in molten salts. These electrode potentials (see [VIG 11a], Chapter 8, equation [8.2.6]) prohibit the electrolysis of their salts in aqueous media. These potentials are: aluminum: -1.66 V; titanium: -1.75 V; magnesium: - 2.03 V; sodium: -2.71 V. This chapter studies the electrolytic extraction processes in aqueous solution. 2.2...
