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RXN Aluminum (Al) FAQ - Q uestion and A nswer Table of Contents:


1. Physical Properties of Aluminum?
2. Thermodynamic Properties of Aluminum?
3. Thermodynamic Properties of Aqueous Solutes of Aluminum?
4. Solubility Products of Slightly Soluble Salts of Aluminum?
5. Stability Constants of Aqueous Complex Ions of Aluminum?
6. Aqueous Standard Reduction Potentials for Aluminum?
7. Where does Aluminum come from?
8. Additional information about Aluminum?

9. Return to the Previous Menu.
10. Return to the RXN Communications Home Page.

Q 1. Physical Properties of Aluminum?
A Source: Metals Handbook, Desk Edition, ASM American Society for Metals , Metals Park, OH, 44073, 1985, ISBN: 0-87170-188-X
Date: June 1986

Atomic Number ........................................ 13
Atomic Weight ........................................ 26.98
Density (g/cm^3) ..................................... 2.70
Density (lb/in^3) .................................... 0.0974
Melting Point (C) .................................... 660
Melting Point (F) .................................... 1220
Boiling Point (C) .................................... 2450
Boiling Point (F) .................................... 4442
Specific Heat (cal/g-C) .............................. 0.215
Specific Heat (J/kg-K) ............................... 900
Heat of Fusion (cal/g) ............................... 94.5
Heat of Fusion (Btu/lb) .............................. 170
Coefficient of linear thermal expansion (uin/in/C) ... 23.6
Coefficient of linear thermal expansion (uin/in/F) ... 13.1
Thermal conductivity (cal/cm^2/cm/sec/C) ............. 0.53
Electrical resistivity (uohm-cm) ..................... 2.6548
Modulus of elasticity in tension (psi) ............... 9,000,000
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Q 2. Thermodynamic Properties of Aluminum?
A Source: Plambek's Molar Thermodynamic Properties of Pure Substances
Link: http://www.chem.ualberta.ca/courses/plambeck/p101/p00403.htm
Date: 16 May 1998

Formula               DH0f       DG0f       S0         C0p
                      kJ/mol     kJ/mol     J/K mol    J/K mol
Al(c)                   0.0        0.0        28.33      24.35
Al(g)                 326.4      285.7       164.54      21.38
Al3+(g)              5483.17        --          --         --
Al(OH)3             -1276.          --          --         --
AlCl3(c)             -704.2     -628.8       110.67      91.84
AlCl3(g)             -583.2         --          --         --
Al2O3(c,,alumina)  -1675.7    -1582.3        50.92      79.04

----------------------------------------------------------------------------
Notes: These molar values apply to pure substances at 25oC and exactly
100000 Pa (1.0 bar or 100 kPa) pressure. One standard atmosphere pressure is
slightly higher, 101325 Pa, but the change in tabulated values between these
two pressures is neglegible for all solids and liquids and minor even for
gases. Physical states are indicated by c (crystalline solid), l (liquid),
and g (gas). Different crystalline structures are designated by common or
mineralogical names. Common names for selected compounds are also given.
Values are taken from U.S.N.B.S. tables of molar thermodynamic properties
(J. Phys. Chem. Ref. Data 11, Suppl. 2 (1982)) unless in italics.
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Q 3. Thermodynamic Properties of Aqueous Solutes of Aluminum?
A Source: Plambek's Molar Thermodynamic Properties of Aqueous Solutes
Link: http://www.chem.ualberta.ca/courses/plambeck/p101/p00404.htm
Date: 16 May 1998

Formula          DH0f       DG0f       S0       C0p
                 kJ/mol     kJ/mol     J/K mol  J/K mol
Al3+           -531.      -485.     -321.7       -

----------------------------------------------------------------------------
Notes: These standard molar values apply to (infinitely) dilute aqueous
solutes at 25oC and exactly 100 kPa (1.0 bar) pressure. One standard
atmosphere pressure is slightly higher, 101.325 kPa, but the change in
tabulated values between these two pressures is neglegible for all solids,
liquids, and ions. It is minor even for gases. Values are taken from
U.S.N.B.S. tables of molar thermodynamic properties (J. Phys. Chem. Ref.
Data 11, Suppl. 2 (1982)) unless in italics.
----------------------------------------------------------------------------
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Q 4. Solubility Products of Slightly Soluble Salts of Aluminum?
A Source: Plambek's Solubility Products of Slightly Soluble Salts
Link: http://www.chem.ualberta.ca/courses/plambeck/p101/p00407.htm
Date: 16 May 1998

Compound   Ksp            
Al(OH)3    2.   x 10-32   

----------------------------------------------------------------------------
Notes: These molar values apply in (infinitely) dilute aqueous solutions at
25C. The values are calculated from U.S.N.B.S. tables of molar
thermodynamic properties unless in italics. Solubility products are the
equilibrium constants for the formation of solutions of the constituent ions
of a slightly soluble salt from the pure solid salt.
----------------------------------------------------------------------------
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Q 5. Stability Constants of Aqueous Complex Ions of Aluminum?
A Source: Plambek's Stability Constants of Aqueous Complex Ions
Link: http://www.chem.ualberta.ca/courses/plambeck/p101/p00408.htm
Date: 16 May 1998

Ion            Constant     log Kstab  

Al(OH)4-       3.30 x 10+33   33.518   

----------------------------------------------------------------------------
Notes: These molar values apply in (infinitely) dilute aqueous solutions at
25oC. The values are calculated from U.S.N.B.S. tables of molar
thermodynamic properties unless in italics. Stability constants are the
equilibrium constants for the formation of the complex ion from its
constituent simpler ions.
----------------------------------------------------------------------------
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Q 6. Aqueous Standard Reduction Potentials for Aluminum?
A Source: Plambek's Aqueous Standard Reduction Potentials
Link: http://www.chem.ualberta.ca/courses/plambeck/p101/p00409.htm
Date: 18 May 1998

Electrode Couple          E0, V     dE0/dT, mV/K
Al3+ + 3e- --> Al         -1.676    +0.532

----------------------------------------------------------------------------
Notes: Values for 0.1 MPa and 25oC in aqueous 1.0 molar acid solution,
calculated from U.S.N.B.S. tables of molar thermodynamic properties unless
in italics. The potential values are given to the nearest 0.1 mV if known,
thermal coefficients to the nearest 0.001 mV/K if known. The thermal
coefficient is that of the isothermal cell in which one of the electrodes is
the standard hydrogen electrode. Ions are all aqueous. Elements and
compounds are pure substances, present in their usual state at 25oC, unless
otherwise indicated. The saturated calomel reference potential is the
experimental value for pure mercury in contact with an aqueous solution
saturated with both Hg2Cl2 and KCl.
----------------------------------------------------------------------------
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Q 7. Where does Aluminum come from?
A Source: The Minerals Council of Australia
Link: http://www.minerals.org.au/facts/al.htm
Date: 2 Oct 1997

Introduction

Aluminium (Al) is the most plentiful metallic element in the Earth's crust. Combined with oxygen and hydrogen, it forms bauxite, the ore most commonly mined for aluminium. Metallic aluminium was first isolated in 1829 from aluminium chloride, but it was not commercially produced until 1886.

Aluminium is a silvery-white, tough, but lightweight metal (specific gravity 2.7). It is a good conductor of electricity and is very resistant to atmospheric corrosion. Because of these properties it has become an important metal. Aluminium alloys combine lightness with strength and as a result are used in a great variety of industries. In Australia, the building and construction industry is the most important consumer.

Occurrence

The main minerals in bauxite are gibbsite (Al203.3H20), boehmite (Al203.H20), and diaspore, which has the same composition as boehmite but is denser and harder. The pure anhydrous oxide of aluminium, alumina (Al203), contains 52.9% aluminium and 47.1% oxygen. Bauxite may be as hard as rock or as soft as mud and it may occur as compacted earth (both friable and re-cemented), small balls (pisolites), or hollow, twig-like material (tubules). Its colours may be buff, pink, yellow, red, or white, or any combination of these.

Bauxite ore refers to bauxite that contains sufficiently high levels of Al203 and suitably low levels of Fe203 and silica to be economically mineable. Other potential sources of aluminium include a variety of rocks and minerals such as aluminous shale and slate, aluminium phosphate rock, and high-alumina clays.

Named after the French district of Les Baux, where it was first discovered in 1821, bauxite is produced by tropical or Semitropical weathering of alumina-bearing rocks. It occurs as a weathered cover or blanket known as laterite, over a variety of rocks. Because of the way it forms, bauxite deposits are generally very extensive. Bauxite is found on just about all the continents of the world. The largest known economic resources of bauxite occur in Australia and Guinea. In terms of ranking, these countries are followed by Brazil, Jamaica, and India. Although the USA, Japan, and the Federal Republic of Germany are the world's largest consumers of aluminium they possess little or no bauxite deposits of their own.

Australian Resources and Deposits

Australia produces about 40% of world bauxite and over 35% of world alumina, making it the largest producer of bauxite and alumina. Bauxite is mined from open cut operations at Weipa (Qld), Gove (NT), and the Darling Range (WA). There are very large bauxite deposits in the Mitchell Plateau and Cape Bougainville regions of Western Australia, but those are not currently economic to mine.

Australia's bauxite resources are assessed each year by the Bureau of Resource Sciences. The assessment is based on published and unpublished data. These estimates are shown on the Mineral Statistics Fact Sheet.

Mining

Extraction of aluminium metal takes place in three main stages - mining of bauxite ore, refining the ore to recover alumina, and smelting alumina to produce aluminium.

Bauxite is mined by surface methods (open cut mining) in which the topsoil and overburden are removed by bulldozers and scrapers and then used for revegetating the area and returning it to sometimes better than original condition or converting it to agricultural land. The underlying bauxite, broken by explosives if necessary, is mined by front-endloaders, power shovels, or hydraulic excavators. Sometimes the bauxite is crushed and washed to remove some of the clay and sand waste and then dried in rotary kilns. Other bauxites may just be crushed or dried. The ore is then loaded into trucks, railway cars, or onto conveyor belts, and transported to ships or refineries.

In nearly all commercial operations, alumina is extracted from the bauxite by the Bayer refining process. The process, discovered by Karl Bayer in 1888, consists of four stages.

(1) Digestion - in which the finely ground bauxite is fed into a steam-heated unit called a digester. Here it is mixed, under pressure, with a hot solution of caustic soda. The aluminium oxide of the bauxite and some of the silica react with the caustic soda forming a solution of sodium aluminate or green liquor and a precipitate of sodium aluminium silicate.

(2) Clarification - in which the green liquor or alumina-bearing solution is separated from the waste (the undissolved iron oxides and silica which were part of the original bauxite and now make up the sand and red mud waste). This stage involves three steps: firstly, the coarse sand-sized waste is removed and washed to recover caustic soda; secondly, the red mud is separated out; and, thirdly the remaining green liquor is pumped through filters to remove any remaining impurities. The sand and mud are together pumped to residue lakes and the green liquor is pumped to heat exchangers where it is cooled from 1000C to around 65O-790C.

(3) Precipitation - in this stage the alumina is precipitated from the liquor as crystals of alumina hydrate. To do this, the green liquor solution is mixed in tall precipitator vessels with small amounts of fine crystalline alumina, which stimulates the precipitation of solid alumina hydrate, as the solution cools. When completed the solid alumina hydrate is passed on to the next stage and the remaining liquor, which contains caustic soda and some alumina, goes back to the digesters.

(4) Calcination - in the final stage the alumina hydrate is washed to remove any remaining liquor and dried. Finally it is heated to about 1000C to drive off the water of crystallisation, leaving the alumina, which is a dry, pure white, sandy material. A portion of the alumina may be left in the hydrate form or further processed for the chemical industry.

All commercial production of aluminium is based on the Hall-Heroult smelting process in which the aluminium and oxygen in the alumina are separated by electrolysis. This consists of passing an electric current through a molten solution of alumina and natural or synthetic cryolite (sodium aluminium fluoride). The molten solution is contained in reduction cells or pots which are lined at the bottom with carbon (the cathode) and are connected in an electrical series called a potline. Inserted into the top of each pot are carbon anodes, the bottoms of which are immersed in the molten solution.

The passage of an electric current causes the oxygen from the alumina to combine with the carbon of the anode forming carbon dioxide gas. The remaining molten metallic aluminium collects at the cathode at the bottom of the pot. Periodically, it issiphoned and transferred to large holding furnaces. Impurities are removed, alloying elements added and the molten aluminium is cast into ingots.

The smelting process is a continuous one. As the alumina content of the cryolite bath is reduced more is added. Heat generated by the passage of the electric current maintains the cryolite bath in its molten state so that it will dissolve the alumina. A great amount of energy is consumed during the smelting process; from 14-16 000 kilowatt hours of electrical energy is needed to produce one tonne of aluminium from about two tonnes of alumina. The availability of cheap electricity is therefore essential for economic production.

Aluminium ingots are produced in various shapes and sizes depending on their end use. They may be rolled into plate, sheet, foil, bars, or rods. They may be drawn into wire which is stranded into cable for electrical transmission lines. Presses extrude the ingots into hundreds of different useful and decorative forms, or fabricating plants may make them into large structural shapes.

A number of factors in the aluminium production cycle relate to the environment, and considerable resources are allocated to minimising the impact of mining, refining, and smelting on the surrounding environment. Mine rehabilitation is carried out, making every effort to return the area to at least its original condition. Extreme care is taken with the handling and disposal of red mud from the refineries. This is usually pumped into dams which are sealed with impervious material to prevent pollution of the surrounding countryside. Strict measures are also taken to minimise fluoride emissions from smelters and dusty or corrosive material from the refineries.

Uses

The production of alumina consumes over 90% of the world's production of bauxite. The remainder is used by the abrasive, refractory, and chemical industries. Bauxite is also used in the production of high-alumina cement, as an absorbant or catalyst by the oil industry, in welding rod coatings and fluxes, and as a flux in making steel and ferroalloys.

Uses of aluminium include the following-electrical equipment; car, ship, aircraft construction; metallurgical and chemical processes; domestic and industrial construction; packaging (aluminium foil, cans); kitchen utensils (cutlery, pans).

The aluminium industry initiated the development of technology for recycling aluminium containing material and setting up its own can collection centres. One of the industry's main incentives has been the reduced amount of energy it takes to produce one tonne of secondary aluminium compared with one tonne of primary aluminium. This involves a saving of 95% of the energy required to produce molten aluminium from bauxite. Each tonne of recycled aluminium also means a saving of seven tonnes of bauxite. In Australia about 10% of aluminium production comes from recycled material.

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Q 8. Additional information about Aluminum?
A Additional information about Aluminum can be found through the following links:

The Alubook offers extensive online information about Aluminum.

Aluminum - Aluminum Industry WWW Server.
ASM - ASM International, the Materials Information Society.
CLI - CLI International's Corrosion and Materials Technology Web Site.
Metal - Metalmart, Incorporated, home page.
RMC - Reynolds Metal Company, aluminum.
TMS - The Minerals, Metals, and Materials Society (TMS).

Additional information about all elements can be found through the following links:

Start WebElements is a link to the Web Elements page.

The University of Illinois at Chicago Thermodynamics Research Laboratory offers a compilation of Thermodynamic Data and Property sites.

The Los Alamos National Laboratory provides an online Periodic Table with supporting data.

The ChemiCool site offers an online Periodic Table and links to Chemistry Calculators.

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