Aluminium and Its Alloys

Aluminium and Its Alloys - EGE UNIVERSITY CHEMICAL...

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Unformatted text preview: EGE UNIVERSITY CHEMICAL ENGINEERING DEPARTMENT Prepared by: 05-06-8091 Mustafa Serkan ACARSER Submitted to: Date: 24.04.2008 Özcan BEŞERGİL May 2008 Bornova-IZMIR Bornova KYK Dormitory Bornova-IZMIR April 24 2008 Mr. Özcan BESERGIL Ege University Department of Chemical Engineering Bornova, Izmir, TURKEY Dear Mr. Beşergil The Research Paper is being submitted for your review and evaluation as per course requirements for Che 116 Technical Communication. The objective of this paper is to introduce you Calcium and Calcium Compounds. In this paper, you will read about history, physical and chemical properties, aluminium alloys, manufacture, health and safety, economic aspects, environmental consideration, uses, import and export. I hope this report meets all of the course requirements. If there are any questions, Please feel free to contact me. Sincerely yours; Mustafa Serkan ACARSER 05-06-8091 Table of Content Summary Introduction 1.0 History 1.1 First Mention of Aluminium 1.2 Aluminium Becomes a Metal 1.3 Industrial Breakthrough 2.0 Properties 2.1 Physical Properties 2.1.1 Refined Aluminium 2.1.2 Crystal Structure 2.1.3 Tabular Overview of the most important properties 2.1.4 Properties and Applications 2.1.5 Electrical Conductivity 2.1.6 Thermal Conductivity 2.1.7 Magnetic Properties 2.1.8 Optical Properties 2.2 Aluminium in the Periodic Table 2.3 Chemical Behaviors of Aluminium 2.3.1 Reactions with Elements and Inorganic Compounds 2.3.2 Reaction with Organic Compounds 3.0 Aluminium Alloys 3.1 What role do Alloys play in the Aluminium Industry? 3.2 Importance and Functions of Aluminium Alloys 3.3 Alloy Forms 3.4 Master Alloys 3.5 Production 3.6 Composition and Available Forms 4.0 Manufacture 4.1 Bauxite and Alumina 4.2 Electrolysis 5.0 Economic Aspects 5.1 Historical Development i ii 1 2 3 4 4 5 6 7 7 7 8 8 8 8 9 10 10 10 11 12 13 13 14 14 19 21 21 5.2 Aluminium as an Economic Factor 5.3 Aluminium Industry in Turkey 6.0 Environmental Conditions 6.1 Environmental Protection in the Aluminium Industry 6.1.1 Raw Materials 6.1.2 Aluminium Extraction 6.1.2.1 Residual Products and Their Disposal 6.1.2.2 Emission 6.1.2.3 Energy 6.1.3 Aluminium Processing 6.1.3.1 Residual Products and Emission 6.1.3.2 Energy 6.1.4 Aluminium Products 6.1.5 Aluminium Recycling 7.0 Uses 8.0 Healthy and Safety 8.1 Aluminium in the Human body 8.2 Aluminium in medicine 8.2.1 Dialysis 8.2.2 Alzheimer’s Disease 8.3 Food and packaging 9.0 Recycling References Appendix 21 22 25 25 25 26 27 27 28 28 28 29 30 31 32 32 33 33 33 35 37 38 Summary I prepared this report fort the Course Che 116 Technical Communication is about Aluminium and Aluminium Alloys. It consists of the nine steps which are listed in the table of contents. I have sum up lots of sources that are listed in the references list to find the most comprehensive and reliable information about my subject. Aluminium is a very useful metal today and I gathered lots of information about the uses areas and applications of aluminium in industry. I tried to explain the production process of aluminium from bauxite to where it’s sold to the final consumer. Also, I explained some information about the history of aluminium. Furthermore, Because of its recycling benefits, I gave some data about recycling facts of aluminium. I decided to search the aluminium because I thought that it is one of the most useful metals in industry and aluminium industry is developing day by day. Also, I think it will be the metal of future. i INTRODUCTION In this report, I will give information about the aluminium metal. There will be information about history of aluminium, the general properties of aluminium, and common applications of aluminium in industry, the economic analysis of aluminium in Turkey and in the world and finally the recycling of aluminium. As mentioned above, I learned very important and interesting facts about aluminium. Especially in part of economic analysis and recycling of aluminium. ii 1.0 History 1.1 First Mention of Aluminium The Roman historian Plinius the Elder (23-79 A.D.) described natural alum stone (a compound of aluminium and sulphur) as “alumen”. The Egyptians were probably using salts obtained from this mineral as a binder in artists’ color paint and textile dyes around 1000 B.C.; the Greeks as well as the Chinese later used the salts. [9] There is an interesting legend associated with alum stone: Plinius described an event that was claimed to have taken place at the time of Emperor Tiberius. He reported how an unknown craftsman made an unusual gift to the emperor: it was a beautiful drinking goblet, which looked like silver but was a lot lighter. Plinius claimed the goblet was made from some sort of unbreakable glass. The craftsman reportedly said that he didn’t want to reveal anything more about it other than that it had been obtained from clay. Was the goblet possibly made from aluminium? If so, the mysterious craftsman was centuries ahead of his time, and he must also have known another, much simpler method of extracting aluminium than the one used today - a method that future generations never found out about. According to the legend, Tiberius ordered that the craftsman be beheaded: he was worried that the new metal would make silver and gold worthless! Alumina There are, of course, one or two question marks surrounding this report by Plinius and one should not take him too literally. Today, we know for certain that in the ensuing centuries the use of alum was limited to its application as a tanning agent and as styptic medication. [12] It was only in the middle of the 18th century that the German chemist Andreas Sigismund Marggraf (1709-1782) discovered the basis of alum: alumina, a compound of a hitherto unknown metal with oxygen. Science was thus made aware of this metal for the first time; however, it was not recognized as being a metal in its own right because it only occurs in nature as a compound with oxygen and silica. [13] Andreas Sigismund Marggraf 1.2 Aluminium Becomes a Metal In 1809, the British scientist Sir Humphry Davy (1778-1829) was the first person to extract aluminium, for a fraction of a second, from alumina, and thus prove the element’s existence. He called it aluminum, which derived from alum. In British English, the spelling was subsequently changed to aluminium; the word ‘aluminum’ continues to be used in the USA. [9] The Danish scientist Hans Christian Oersted (1777-1851) was the first person to prepare the pure metal, in 1825. He described his discovery thus: “It forms a lump of metal that resembles tin in color and sheen.” However, he forwent any further experiments and passed his results on to the German chemist Friedrich Wöhler (1800-1882). Inspired by Oersted, but using an improved method, Wöhler also managed to produce pure aluminium. Later on, he managed to ‐ 1 ‐ Sir Humphry Davy produce it in larger lumps and was the first to determine the element’s important chemical and physical properties, such as density, electrical conductivity, corrosion resistance and combustibility. [4] Robert Wilhelm Bunsen, who had produced magnesium using the electrolysis of magnesium chloride, also succeeded in extracting aluminium in 1854, using the electrolysis of sodium aluminium chloride. It was notable here that at almost the same time another chemist working independently of Bunsen had the same idea. It was this chemist who started producing aluminium on a commercial scale. [14] The person concerned was the French chemist Henri Etienne Sainte-Claire Deville (1818-1881), who used Wöhler’s findings in 1854 to develop the first practical method of extracting aluminium. Like Wöhler, he used aluminium chloride as his starting material but instead of using expensive potassium as the reducing agent he used sodium, which was cheaper. Sodium combines with chlorine and produces sodium chloride, common salt, leaving aluminium as the product. [13] Thus, for the first time, the production of aluminium on an industrial scale was now within the realms of possibility. Sainte-Claire Deville presented an aluminium ingot as ‘silver from clay’ at the World Exhibition in Paris in 1855, which aroused great interest. In those days, the metal was significantly more expensive than gold. With the support of Emperor Napoleon III, who was hoping to develop lightweight body armor (cuirassier) for his cavalry, he built several production facilities in the ensuing years; for decades, these plants produced all of the world’s aluminium. [15] Sainte-Claire Deville giving a lecture Hans Christian Oersted Friedrich Wöhler Henri Etienne Sainte-Claire Deville 1.3 Industrial Breakthrough Working independently of each other, the French engineer Paul Louis Toussaint Héroult (1863-1914) and the American chemist Charles Martin Hall (1863-1914), both filed patents for fused-salt electrolysis in 1886. In this process, which is also known as the Hall-Héroult process, alumina is melted together with cryolite, a mineral that is found in Greenland, dissolved and broken down using an electric current; this enables aluminium to be extracted. In a long drawn-out legal battle between Hall and Héroult over patent rights, Hall was granted a patent for the USA and Héroult’s claims were recognized in all other countries. [16] Their method of extraction, which was far cheaper than Sainte-Claire Deville’s process, enabled aluminium to be used for the first time on a large scale. The ‐ 2 ‐ Paul Louis Toussaint Héroult method was made possible by the discovery of the dynamo 20 years earlier by Werner von Siemens, which enabled electric current to be generated in large quantities, and the development of the so-called Bayer Process for producing alumina; this process is named after the Austrian chemist Karl Joseph Bayer (1847-1904) who developed it and was granted German patents for it in 1887 and 1892. Alumina is obtained from bauxite, a mineral that was first found in the French village of Les Baux in 1822 (hence the name) and which has a high alumina content of about 50 per cent. This led to bauxite becoming practically the only raw material used for aluminium extraction. The final breakthrough for aluminium to establish a broad range of applications only came later when the German engineer Alfred Wilm discovered by chance in 1906 that small quantities of copper, manganese, magnesium and silicon led to significant increases in aluminium’s mechanical properties. This discovery laid the foundation for a branch of metallurgy devoted specifically to aluminium, and its development into a widely usable constructional material. [9] View inside a potroom ‐ 3 ‐ Charles Martin Hall 2.0 Properties 2.1 Physical Properties 2.1.1 Refined Aluminium Aluminium is classified as ‘refined’ if it has a purity of 99.95% or more. Aluminium with a purity of 99.99% was first produced in 1920. Today, so-called ‘zone refining’ can be used to produce aluminium with a purity of 99.9996%. Such highly refined and very expensive grades of aluminium are mainly used for electrical, semiconductor and cryogenic applications. Aluminium is an element that belongs to Group IIIA of the Periodic Table. Its atomic number is 13; this means an aluminium atom has 13 electrons, which are distributed in three shells around the atomic nucleus. The atomic mass is 26.981538. [3] 2.1.2 Crystal Structure Most materials form crystals when they solidify from the liquid state. The structure of these crystals depends on the material type. If there is mutual attraction between atoms and other atoms or ions (electrically charged particles) such that they are arranged regularly, one refers to this arrangement as a crystal lattice. Aluminium atoms crystallise to produce a facecentred cubic lattice. The smallest unit of the aluminium space lattice, namely the unit cell, is cube shaped, with an aluminium atom at each of the corners and in the centre of each of the faces of the cube. The alloying elements used with aluminum usually have a different shaped crystal lattice: for example, the crystal lattice of silicon is diamond-shaped, with magnesium it is a simple cube and with iron it is a body-centred cube; however, with copper it is also face-centred cubic. (See in figure 1) [5] Figure 1: Face-centred cubic lattice [9] ‐ 4 ‐ 2.1.3 Tabular Overview of the most Important Properties Certain physical properties are fixed (e.g. atomic mass), whereas some others (e.g. density and specific heat) are dependent on the environment, especially temperature. Some properties (e.g. electrical conductivity) are very sensitive to alloying additions or structural changes. Where these dependencies are of practical significance, they will be dealt with in more detail in the following sections. (See in table 1) [1] Table 1: Physical Properties of Aluminium [5] PROPERTY VALUE UNIT Atomic number 13 Relative atomic mass 26.98154 -6 Atomic volume 9.996·10 Density(25oC) 2.6989·10³ Crystal lattice g m³.mol-1 g.cm³ face-centered cubic o Lattice constant (25 C) 0.40496 Nm Melting point 660.3 ºC Boiling point 2520 ºC Thermal conductivity (25oC) 236 W.m-1·K-1 Young's modulus (refined aluminium) 67 kN.mm-² Resistivity 2.66·10-8 W.m Specific heat at constant pressure 0.9 kJ.kg-1·K-1 Linear coefficient of expansion (25ºC) 23.5·10-6 1.K-1 Electrical conductivity (refined aluminium) 37 m·mm-² 2.1.4 Properties and Applications Density: Low density is one of the most important properties of aluminium because light weight makes a major contribution to its range of applications. With commercially pure aluminium it is some 2.6 to 2.8·x 10³ kg/m³ which is about a third of the density of steel. Low density results in significant weight reductions and leads to aluminium’s use in motor vehicles and other means of transport in the air, on land or on water, as well as items such as containers that have to be moved or transported regularly. Low density leads to energy savings and favourable operating and maintenance costs. Density is temperature-dependent and decreases with increasing temperature as a result of thermal expansion. The diagram below clearly shows this temperature dependence. [1] ‐ 5 ‐ Figure 2: Temperature dependence diagram [17] Coefficient of thermal expansion: The coefficient of thermal expansion is a material-specific property that indicates the relative expansion in the length or volume of a material for each degree Celsius rise in temperature. One can use it to calculate the amount by which a material will expand when heated through a certain temperature range. The coefficient of thermal expansion of aluminium increases with increasing temperature. The following table shows values for refined aluminium (Al99,99). Any possible alloying elements will also have an effect on the coefficient of thermal expansion. [4, 6] Table 2: Coefficient of thermal expansion of Al99,99 [17] Specific heat: The specific heat indicates how much thermal energy is required to heat a kilogram of a substance by 1 °C. The unit of measure is J/kg K. One can use the specific heat to determine how much energy is required to heat a substance to a given temperature. In the solid state, the specific heat of aluminium increases steadily from a value of 0 at 0 K until it reaches a maximum value at the melting point (cf. table below). This means that the warmer the (solid) material becomes the more energy that is needed to heat it still further. [9] Table 3: Specific heat of refined aluminium (Al99,99) [17] ‐ 6 ‐ 2.1.5 Electrical Conductivity The electrical conductivity of aluminium with a 99.99% degree of purity is 63.8% of the International Annealed Copper Standard. On a weight-to-weight basis, however, the electrical conductivity of aluminium is about twice that of copper. For this reason, aluminium has been used exclusively in overhead power lines for a good many years. Electrical conductivity depends on chemical composition and microstructure as well as on heat treatment (the so-called ‘alloy temper’). Electrical conductivity measurements are actually used to check certain age-hardenable alloys after heat treatment. The following figure shows the interrelationship between electrical conductivity, cold work and intermediate annealing temperature for unalloyed aluminium Al99,5. [1] Figure 3: Electrical conductivity of unalloyed aluminium (Al99,5) [17] 2.1.6 Thermal Conductivity The thermal conductivity of standardised aluminium-based materials is in the range 80 to 230 W/m·K. On a weight-to-weight basis it is thus about twice that of copper. The good thermal conductivity is put to beneficial use in many fields of application, such as pistons, cylinders and cylinder heads for internal combustion engines and compressors, and all types of heat exchanger. The mechanism of thermal conductivity is similar to that of electrical conductivity. [4, 1] 2.1.7 Magnetic Properties Aluminium and aluminium alloys are very weakly paramagnetic, i.e. they are only very weakly attracted by a magnet. Alloying elements only have a negligible effect so that aluminium alloys can be regarded as being practically non-magnetic. Use is made of this property, for example, to shield sensitive electronic equipment. [9] ‐ 7 ‐ 2.1.8 Optical Properties Aluminium has good optical properties: the bare-metal surface has a high reflectivity for light, heat and electromagnetic radiation over a wide range of wavelengths. At the same time, high reflectivity means that there is little absorption of incident radiation. This property is coupled with a low emissivity, i.e. low radiation of heat. Aluminium is thus particularly well suited for use in reflectors and as protection against radiant heat and radiation losses. The interaction between material and radiation is limited to the region near the surface. Consequently, optical properties are critically dependent on surface condition; they can be crucially affected by surface treatment. A part of the energy of the incident radiation is reflected and the rest is absorbed. Reflectivity usually depends on the wavelength and thus on the type and temperature of the radiation source. [4, 1] 2.2 Aluminium in the Periodic Table Aluminium (Al) belongs to Group IIIA of the Periodic Table, the boron group. This group also includes boron, gallium, indium and thallium. Elements that belong to the same group have a similar electron configuration: all the atoms of the elements in the boron group have three electrons in the outermost layer, which allow the elements to combine with other elements. The elements of Group IIIA are all metals with the exception of boron, which is a metalloid (i.e. it has the characteristics of a metal and a non-metal). The elements are quite reactive and are therefore only ever found as compounds in nature, never in the pure form. The hardness of the metals in this group decreases as one goes from the top of the group to the bottom. Aluminium is by far the most common element in the boron group. In nature, aluminium is always found combined with oxygen, for which it has a high affinity. [6, 7] 2.3 Chemical Behaviors of Aluminium 2.3.1 Reactions with Elements and Inorganic Compounds Aluminium reacts with oxygen, O2, having a heat of reaction of Al2O3 produced. 2 Al + 3 2 O 2 ⎯ ⎯⎯ A l 2 O 3 → In dry air at room temperature this reaction is self-limiting, producing a highly impervious film of oxide ca 5 nm in thickness. The film provides both stability at ambient temperature and resistance to corrosion by seawater and other aqueous and chemical solutions. At high temperatures, aluminium reduces many oxygen-containing compounds, particularly metal oxides. These reactions are used in the manufacture of certain metals and alloys, as well as in the thermite welding process. 2 M O + 2 A l ⎯ ⎯⎯ A l 2 O 3 + 3 M → ‐ 8 ‐ Molten aluminium reacts violently with water and the molten metal should not be allowed to touch containers. In finely divided powder form, aluminium also reacts with boiling water to form hydrogen and aluminium hydroxide; this reaction proceeds slowly in cold water. Aluminium does not combine directly with hydrogen, but it does react with nitrogen, N2, sulfur, and carbon in oxygen-free atmospheres at high temperatures. Very high purity aluminium, resistant to attack by most acids, is used in the storage of nitric acid, concentrated sulfuric acid, organic acids, and other chemical reagents. It also reacts to form a volatile aluminium chloride when heated in a current of dry oxygen-free chlorine or hydrogen chlorine. Aluminium is attacked by salts of more noble metals. In particular, aluminium and its alloys should not be used in contact with mercury or mercury compounds. [1] 2.3.2 Reaction with Organic Compounds Aluminium is not attacked by saturated or unsaturated, aliphatic or aromatic hydrocarbons. The chemical stability of aluminium in the presence of alcohols is very good and stability is excellent in the presence of aldehydes, ketones, quinines. Organic compounds that form with aluminium other than through a direct metal –to-carbon bond include the metallo-orgaics, represented as Al-X-R where X may be oxygen, nitrogen or sulfur and R is a suitable organic radical. The alcholates or alkoxides are compounds of this type where R is alcohol. [1] ‐ 9 ‐ 3.0 Aluminium Alloys 3.1 What role do Alloys play in the Aluminium Industry? For practical applications, aluminium is usually alloyed with other elements, mostly with other metals. This enables the properties of the basis metal to be improved considerably. Alloying produces improvements in aluminium’s properties, such as protection against corrosion by certain substances. A few per cent magnesium, for example, make it resistant to seawater and thus suitable for shipbuilding. Generally speaking, by choosing the right alloying elements, aluminium can be optimised for a specific application. Not least because of this, aluminium alloys have acquired a special importance in many technical fields. Strictly speaking, commercial-purity aluminium, with an aluminium content of up to 99.9%, is also an alloy. Although the iron and silicon contents here are regarded as impurities, they affect the properties of aluminium significantly. In the aluminium industry, one generally differentiates between casting and wrought alloys: casting alloys can only be shaped by casting and are not subjected to subsequent forming. Here, magnesium, silicon and copper are the alloying elements most widely used. By contrast, wrought alloys are intended to undergo deformation using processes such as extrusion, rolling or forging and thus need to have good formability. Important alloying elements here are magnesium, silicon, copper, manganese, zinc and iron. 3.2 Importance and Functions of Aluminium Alloys The properties of aluminium depend on a whole range of factors. The other elements that are present in commonly used alloys, either as deliberate additions or as impurities, play a particularly important role. With the exception of refined aluminium (Al99,99), the aluminium used on a commercial scale is always in the form of an aluminium alloy containing additional elements. Unalloyed or very weakly alloyed aluminium is mainly used to produce foil and strip, chemical equipment and products for electronic and electrical engineering applications. The purpose of alloying is to improve the properties of aluminium, especially strength – most unalloyed metals are soft – and corrosion resistance. The main alloying elements used with aluminium are copper (Cu), silicon (Si), magnesium (Mg), zinc (Zn) and manganese (Mn).); lead, boron, chromium, nickel, titanium, bismuth and zirconium are also used in small quantities. When only present in quantities of a few per cent, or even fractions thereof, each of these elements improves certain properties of aluminium, often at the expense of other properties so that another element has to be added to cancel out this detrimental effect. ‐ 10 ‐ Copper Silicon Magnesium Aluminium alloys are produced by melting, sintering (manufacture of shaped parts using metal powder that is fused together at elevated temperatures) or mechanical mixing. One differentiates between casting alloys and wrought alloys depending on the how the alloys are intended to be processed further. [4] Zinc die-casting 3.3 Alloy Forms Casting alloys are alloys that contain a total of up to 20% silicon, magnesium and copper as alloying elements and can only be formed by casting. The starting material is usually secondary aluminium (aluminium recovered from scrap). Here, the need for favourable casting properties is of primary concern. In addition, the compositions of casting alloys are tailored to the respective casting process (sand casting, permanent-mould casting or die-casting) to be used. Alloys with a silicon content of 5 to 20% have the most favourable casting properties. (See in figure 4) Manganese Figure 4: The most important casting alloys [17] Wrought alloys contain up to 10% alloying elements and are chosen for their good formability. One differentiates between age-hardenable and non-age-hardenable wrought alloys: • • In non-age-hardenable alloys, all of the alloying elements are present in solid solution. These alloys are readily formable. In age-hardenable alloys, the alloying elements are present at room temperature in the form of precipitates. Their distribution determines the strength of the alloy. By subjecting the alloy to a solution heat treatment, the elements are dissolved completely in solid solution and quenching then ensures that this condition is ‘frozen in’ at room temperature. Ageing then results in precipitates forming. The addition of magnesium produces alloys that are non-age-hardenable but resistant to seawater. Duraluminium, the famous aluminium alloy developed by Alfred Wilm in 1909 ‐ 11 ‐ using additions of copper, manganese and magnesium, is an example of an age-hardenable alloy. With wrought alloys, plastic deformation is of primary concern. The most widely used agehardenable wrought aluminium alloys are those that contain magnesium, silicon, manganese, copper and zinc. [18] (See in Figure 5) Figure 5: The most important wrought alloys [17] 3.4 Master Alloys Aluminium master alloys are alloys that are added to molten metal to obtain the desired composition and/or influence the as-cast structure. Master alloys can contain more than 50 weight per cent of the main alloying element. They can be produced by melting or by mixing the individual constituents and then compacting them. One differentiates between two significantly different types of master alloy: • concentrated binary master alloys • grain-refining master alloys Binary master alloys are used to finely adjust the alloy composition; grain-refining master alloys are used to influence the as-cast structure, i.e. the as-cast grain structure. The latter are only added in small quantities. When it comes to influencing the grain structure, one differentiates between the following terms: Grain refinement: The aluminium grain structure is made finer by use of additions of master alloys such as Al-Ti-B, Al-Ti, Al-B oder Al-Ti-C. ‐ 12 ‐ Modification: This is refinement of the eutectic in Al-Si alloys by means of Al-Sr alloys or sodium. Silicon refining: This involves transformation of lamellar silicon into a granular shape and refinement of the primary silicon in hypereutectic aluminium-silicon alloys by means of a phosphorus treatment, i.e. the use of master alloys such as Cu-P, Fe-P or Ni-P, or phosphoruscontaining additives. The use of master alloys is indispensable in melting and casting plants. Master alloys make short alloying times possible, something that is important with alloying elements that have high melting points (iron, titanium, nickel, etc.). In addition, the use of master alloys reduces the loss of alloying elements in the melt. This is particularly important with expensive alloying elements and where metals have a high vapour pressure and/or high oxygen affinity. In addition, master alloys allow toxic metals to be added safely. 3.5 Production Different processes are available for producing master alloys depending on the alloy system concerned: • Dissolution of the elements to be alloyed in a molten metal • Aluminothermic of compounds with excess aluminium • Production of pressed shapes from metal powder Other processes are occasionally used, such as carbothermic reduction, reduction using magnesium or fused-salt electrolysis. The production of master alloys from aluminium scrap as part of the aluminium recycling process is practically only possible by dissolving the alloying elements in the molten metal, either in solid or liquid form. 3.6 Composition and Available Forms When it comes to composition, the most important quality requirement for binary master alloys is their purity. Master alloys are only allowed to contain very small amounts of incidental elements and non-metallic inclusions to avoid adding impurities to the melt. With respect to the purity of grain-refining master alloys, the same requirements apply as for binary master alloys, namely the amounts of metallic and non-metallic impurities must be kept to a minimum. Other important quality criteria for grain-refining alloys are their effectiveness and a uniform size and distribution of the nucleus-forming particles. The most commonly available forms of master alloy are ingots, platelets, granules, pieces cut from direct-chill castings, wire and pressed shapes made from metal powder. ‐ 13 ‐ 4.0 Manufacture 4.1 Baxute and Alumina Bauxite occurs close to the surface in seams varying from one meter to nine meters, formed as small reddish pebbles (pisolites). The ore is shipped to Gladstone following "beneficiation" to remove low-grade material, and blending to provide a consistent grade. The Bayer Process The Bayer Process - an economical method of producing aluminium oxide - was discovered by an Austrian chemist Karl Bayer and patented in 1887. The process dissolves the aluminium component of bauxite ore in sodium hydroxide (caustic soda); removes impurities from the solution; and precipitates alumina tri hydrate which is then calcined to aluminium oxide. A Bayer Process plant is principally a device for heating and cooling a large re circulating stream of caustic soda solution. Bauxite is added at the high temperature point, red mud is separated at an intermediate temperature, and alumina is precipitated at the low temperature point in the cycle. Bauxite usually consist of two forms of alumina - a mon hydrate form Boehmite (Al2O3.H2O) and a tri hydrate form Gibbsite (Al2O3.3H2O). Boehmite requires elevated temperatures (above 200°C) to dissolve readily in 10% sodium hydroxide solution. The tri hydrate grade bauxite is mainly Gibbsite which dissolves readily in 10% sodium hydroxide solution at temperatures below 150°C. Consequently, monohydrate bauxite undergoes high temperature extraction under pressure in digesters, while tri hydrate grade material is added as”sweetening bauxite" to the flash tanks where temperatures are less than 200°C. The design of the plant meets the requirement of smelters of coarse or sandy alumina for reduction to aluminium. The recovery rate is about one tonne of alumina per 2.2 tonnes of bauxite. From the plants, million-tonne bauxite stockpile to the A-frame alumina storage sheds is a processing journey of about 2.5 days. [20] ‐ 14 ‐ Process: 1. DIGESTION OF BAUXITE Grinding: Pisolitic, monohydrate-grade bauxite sized to a maximum of 20 mm, is ground in 10 mills (each with one compartment of rods and one of balls) to allow better solid liquid contact during digestion. Recycled caustic soda solution is added to produce a pump able slurry, and lime is introduced for phosphate control and mud conditioning. Desilication: The silica component of the bauxite is chemically attacked by caustic soda, causing alumina and soda losses by combining to form solid desilication products. To de silicate the slurry prior to digestion, it is heated and held at atmospheric pressure in pre-treatment tanks, reducing the build-up of scale in tanks and pipes. Most desilication products pass out with the mud waste as sodium aluminium silicate compounds. Digestion: The plant has three digestion units. The monohydrate slurry is pumped by high pressure pumps through two agitated, vertical digester vessels operating in series. Mixed with steam and caustic solution, alumina in the bauxite forms a concentrated sodium aluminate solution leaving un dissolved impurities, principally inert iron and titanium oxides and silica compounds. Reaction conditions to extract the monohydrate alumina are about 250°C and a pressure about 3500 kPa, achieved by steam generated at 5000 kPa in coal-fired boilers. Under these conditions, the chemical reactions are rapid: 2NaOH + Al2O3 .3H2O ⎯⎯⎯ 2NaAlO2 + 4H2O → 2NaOH + Al2O3 .H2O ⎯⎯⎯ 2NaAlO2 + 2H2O → By sizing the vessel to optimum holding time, about 97% of the total available alumina is extracted and the silica content of liquor is reduced. ‐ 15 ‐ Heat Recovery: After digestion about 30% of the bauxite mass remains in suspension as a thin red mud slurry of silicates, and oxides of iron and titanium. The mud-laden liquor leaving the digestion vessel is flash-cooled to atmospheric boiling point by flowing through a series of flash vessels which operate at successively lower pressures. The flash steam generated is used to preheat incoming caustic liquor in tubular heat exchangers located parallel to the flash tank line. Condensate from the heat exchangers is used for boiler feed water and washing waste mud. Sweetening: The tri hydrate bauxite has separate grinding and pre-treatment facilities. During the pass through the flash tanks, this additional bauxite slurry with high tri hydrate alumina content is injected to maximize the alumina content of the liquor stream. This occurs in the appropriate flash vessels when the slurry from the digesters has been cooled to less than 200°C. [20,21] 2. CLARIFICATION OF THE LIQUOR STREAM Settlers: Most red mud waste solids are settled from the liquor stream in single deck 40 meter diameter settling tanks. Flocculants are added to the settler feed stream to improve the rate of mud settling and achieve good clarity in the overflow liquor. Washers: The mud is washed with fresh water in counter-current washing trains to recover the soda and alumina content in the mud before being pumped to large disposal dams on Boyne Island. Slaked lime is added to dilute caustic liquor in the washing process to remove carbonate (Na2CO3) which forms by reaction with compounds in bauxite and also from the atmosphere and which reduces the effectiveness of liquor to dissolve alumina. Lime regenerates caustic soda, allowing the insoluble calcium carbonate to be removed with the waste mud. Na2CO3 + Ca ( OH )2 ⎯⎯⎯ CaCO3 + 2NaOH → ‐ 16 ‐ Filters: Settlers overflow liquor containing traces of fine mud is filtered in Kelly-type constant pressure filters using polypropylene filter cloth. Slaked lime slurry is used to produce a filter cake. Mud particles are held on the filter leaves for removal and treatment in the mud washers when filters are sequentially taken off line. Heat Interchange: With all solids removed, the pregnant liquor leaving the filter area, contains alumina in clear supersaturated solution. It is cooled by flash evaporation, the steam given off being used to heat spent liquor returning to digestion. 3. PRECIPITATION OF ALUMINA HYDRATE Crystallization: Dissolved alumina is recovered from the liquor by precipitation of crystals. Alumina precipitates as the tri hydrate Al2O3.3H2O in a reaction which is the reverse of the digestion of tri hydrate 2NaAlO2 + 4H2O ⎯⎯⎯ Al2O3 .3H2O + 2 NaOH → The cooled pregnant liquor flows to rows of precipitation tanks which are seeded with crystalline tri hydrate alumina, usually of an intermediate or fine particle size to promote crystal growth. Each precipitation tank is agitated, with a holding time of about three hours. During the 25-30 hours pass through precipitation, alumina of various crystal sizes is produced. The entry temperature and the temperature gradient across the row, seed rate and caustic concentration are control variables used to achieve the required particle size distribution in the product. ‐ 17 ‐ Classification: The finished mix of crystal sizes is settled from the liquor stream and separated into three size ranges in three stages "gravity" classification tanks. The primary classifiers collect the coarse fraction which becomes the product hydrate. The intermediate and fine crystals from the secondary and tertiary classifiers are washed and returned to the precipitation tanks as seed. Spent Liquor: Spent caustic liquor essentially free from solid overflows from the tertiary classifiers and is returned through an evaporation stage where it is re concentrated, heated and recycled to dissolve more alumina in the digesters. Fresh caustic soda is added to the stream to make up for process losses. [20, 21] 4. CALCINATION OF ALUMINA Washing: A slurry of coarse hydrate (Al2O3.3H2O) from the primary thickeners is pumped to hydrate storage tanks and is filtered and washed on horizontal-table vacuum filters to remove process liquor. Calcining: The resulting filter cake is fed to a series of calcining units - an 1800 tonnes a day circulating fluidized bed calciner or one of nine rotary kilns each 100m long and 4m in diameter. The feed material is calcined to remove both free moisture and chemically-combined water. Firing-zone temperatures above 1100°C are used, achieved by firing with natural gas. The circulating fluidized bed calciner is more energy efficient than the older rotary kilns. Product sandy alumina particles are 90%+ 45 µm (microns) in size. Cooling: Rotary or satellite coolers are used to cool the calcined alumina from the rotary kilns, and to pre-heat secondary combustion air for the kilns. Fluidized-bed coolers further reduce alumina temperature to less than 90°C before it is discharged on to conveyor belts which carry it to storage buildings where it is stockpiled for shipment.[20, 21] ‐ 18 ‐ 4.2 Electrolysis Aluminium primary smelting and casting Primary aluminium is produced in reduction plants (or "smelters"), where pure aluminium is extracted from alumina by the Hall-Héroult process. The reduction of alumina into liquid aluminium is operated at around 950 degrees Celsius in a fluorinated bath under high intensity electrical current. This process takes place in electrolytic cells (or "pots"), where carbon cathodes form the bottom of the pot and act as the negative electrode. Anodes (positive electrodes) are held at the top of the pot and are consumed during the process when they react with the oxygen coming from the alumina. There are two types of anodes currently in use. All potlines built since the early 1970s use the prebake anode technology, where the anodes, manufactured from a mixture of petroleum coke and coal tar pitch (acting as a binder), are ‘pre-baked’ in separate anode plants. In the Soederberg technology, the carbonaceous mixture is fed directly into the top part of the pot, where ‘self-baking’ anodes are produced using the heat released by the electrolytic process. At regular intervals, molten aluminium tapped from the pots is transported to the cast house where it is alloyed in holding furnaces by the addition of other metals (according to the user’s needs), cleaned of oxides and gases, and then cast into ingots. These can take the form of extrusion billets, for extruded products, or rolling ingots, for rolled products, depending on the way it is to be further processed. Aluminium mould castings are produced by foundries which use this technique to manufacture shaped components. World-wide trends in production are shown in the following graph. Aluminium output has increased by a factor of 13 since 1950; making aluminium the most widely used non-ferrous metal. In 1998, world-wide production of primary aluminium was about 22.7 million tonnes per year for and installed capacity of 24.8 million tonnes. The Hall-Heroult method of aluminium production occurs in large refractory-lined steel containers called pots that are connected in series and housed in long buildings called pot rooms. Figure 6: Electrolysis Process ‐ 19 ‐ A. Suspended above each cathode are several closely arranged carbon blocks that serve as the anode (positive electrode). The anodes are suspended by rods in the bath of molten electrolyte in which the alumina is dissolved. B. An electric current of up to 315 000 amps enters the pot via the anode blocks and reduces the alumina by electrolysis into aluminium and oxygen. The oxygen is deposited on the carbon anode where it burns the carbon to form carbon dioxide. The aluminium, being heavier than the electrolyte, collects at the base of the pot. The equation for the basic reaction is: 2Al2O3 + 3C ⎯⎯⎯ 4Al + 3CO2 → C. Each pot consists of a steel shell that is lined with refractory and carbon blocks to serve as the cathode (negative electrode). D. Cryolite, the predominant constituent of the electrolyte, is a sodium aluminium fluoride salt which, when held molten at a temperature of around 960°C, can dissolve alumina. [22, 4] ‐ 20 ‐ 5.0 Economic Aspects 5.1 Historical Development In terms of the date of its discovery compared with other metals, aluminium is a relatively young metal. Shortly before the turn of the 20th century, people marveled at aluminium, an expensive rarity. Around 1900, the total world production of aluminium was about 6,700 tonnes in five countries: USA, Switzerland, France, Germany and UK. Since then, the aluminium industry has recorded continual growth in production. Just over 100 years have elapsed between the beginnings of the industrial production and use of the metal and its widespread use. During this period the aluminium industry has established itself as a significant and important economic sector. Above all, it is the metal’s wide range of properties and the fact that it is possible to combine these in an intentional manner that have contributed to this development. This has led to aluminium being used in many fields of industry. [4] 5.2 Aluminium as an Economic Factor Aluminium has already acquired an enormous economic significance although it has only been extracted and processed on an industrial scale for just over a hundred years. The production of primary and secondary aluminium has increased continually over the years and aluminium parts are now used in large sectors of the economy, not least in the transport and building and construction industries. After steel, aluminium is the most widely used metal today. Today, aluminium is not only a metal with a range of diverse uses, that is to be found in all spheres of everyday life, but it is also a driving force for technological progress that promotes innovations for creating prosperity. These attributes make the aluminium industry a sector with good growth prospects. It provides jobs and income for about 200,000 employees in Europe. They are employed at some 3,000 plants and the European aluminium industry generates an annual turnover of 25bn Euros. The following statistics show the worldwide development of the production of primary and secondary aluminium: World primary aluminium production ‐ 21 ‐ World secondary aluminium The economic significance of the aluminium industry cannot be expressed in mere figures. It also has an influence on every sector with which it is linked, upstream or downstream. In order to fulfil its role as a cornerstone of technological progress and product innovation, most investments in plant and equipment are made in the field of application-oriented research and development. Furthermore, one needs to maintain international competitiveness and consequently safeguard domestic business locations. [1, 4] Figure 7: Worldwide Primary Aluminium Production by Geographic Region kg Aluminium Consumption per body (Kg) Ita l Sw ay ed en N or w ay A us G tria er m an D en y m ar k Fr an B ce el gi u Gm re ec e Fi nl an d En gl an d S Po pa in rt ug us e Tu rk ey N et h er la nd s 45 40 35 30 25 20 15 10 5 0 Figure 8: Aluminium Consumption per body (kg) 5.3 Aluminium Industry in Turkey In 1950s, aluminium was started to be used in Turkey. Because of the increasing demand of aluminium from 1960s, government started to search baxuite reserves. So, in 1967, Seydişehir Aluminium Facilities was set up. In 1990, sector started to import some aluminium products. The production of aluminium in Turkey increased from 2000s.The consumption of aluminium per body is 3.8 kg and the mean value in European countries is 22.0 kg. This shows that there ‐ 22 ‐ will be a great consumption potential in Turkey in the future. In 2001-2005 periods the import of aluminium in turkey has an increasing slope. Germany has the largest import market of Turkey. (23) But, although all of them, Turkey has also an increasing export chart. Plates, sheets and strips are the common exported products. See figure 9 Export of Aluminium in Turkey 2001-2005 700 600 x 100 US $ 500 Seri 1 400 300 200 100 0 2001 2002 2003 2004 2005 2006 Figure 9: Export of aluminium in Turkey Also to see the place of Turkey in the world exportation and importation of aluminium see Figure 10 and Figure 11. Turkey Netherlans United Canada Belgium Korea China Italy France Japan Germany USA x100000 US$ International Aluminium Imports 14,00 12,00 10,00 8,00 6,00 4,00 2,00 0,00 Figure 10: International aluminium imports ‐ 23 ‐ Figure 11: International aluminium exports ‐ 24 ‐ U K Tu rk ey or w ay A us tra li a Fr an N ce et he rla ns B el gi um N U hi na C G er SA 8,00 7,00 6,00 5,00 4,00 3,00 2,00 1,00 0,00 m an y C an ad a R us si a x100.000 US$ International Aluminium Exports 6.0 Environmental Conditions 6.1 Environmental Protection in the Aluminium Industry The aluminium industry supports the objectives of sustainable development. The use of aluminium helps satisfy people’s basic needs but also offers some benefits from an ecological point of view: firstly, it preserves the environment by rehabilitating bauxite mines and via recycling; secondly, it uses fossil fuels sparingly because the aluminium industry meets most of its energy requirement from environmentally friendly and inexhaustible hydroelectricity; and thirdly, the use of relatively light aluminium products results in energy savings, such as in transportation. However, the main benefit of aluminium from an ecological point of view is without doubt its recyclability; used aluminium products can be turned into new ones without any loss in quality or value using a relatively small amount of energy. Thus, aluminium remains in a closed material loop, resources are conserved and less waste is produced. This means the production and use of aluminium is compatible with the demands of environmental protection and the principles of sustainability. This often proves profitable from an economic point of view, too. In particular, the recycling of aluminium and operating and auxiliary materials is an extremely valuable and efficient means of protecting the environment and striving to adhere to the principles of sustainability. 6.1.1 Raw Materials About 120 million tonnes of bauxite are mined annually for the extraction of aluminium. Even today’s known commercially viable bauxite reserves will last for more than 200 years – without taking into account the continually increasing use of recycled aluminium (secondary aluminium). The layers of topsoil removed during bauxite mining are stored temporarily, to be used later to cover over the mines again once mining activities have ceased. The respective measures and planning for this begin long before bauxite mining begins. The vegetation is first removed and seeds are collected. Immediately prior to the start of mining, the humus layer is removed, enriched with the seeds of native plants and then stored. Once mining has been completed, the subsoil is loosened to aerate it and facilitate root growth, and the humus layer is applied again. Grass is first sown as protection against erosion and the seeds of native plants are sown later. Bauxite Bauxite mine before rehabilitation ‐ 25 ‐ After bauxite mining ceases, 80% of the area is returned to its original vegetation in this way, 18% is developed for forestry and agricultural purposes and 2% is used for industrial or recreational purposes. Thus, bauxite mining is basically the temporary use of the respective land. The whole mining process is continually monitored in order to avoid erosion and ensure that waste is disposed of in a pre-determined manner. The most important a bauxite deposits are located near the equator and about 18% of the bauxite mined annually comes from rain forest regions. The area required for mining there is about two square kilometers a year. In these areas in particular one usually tries to achieve a form of rehabilitation that is as close as possible to the original vegetation in order to preserve the balance of the local eco-system. Bauxite mine after rehabilitation 6.1.2 Aluminium Extraction 6.1.2.1 Residual Products and Their Disposal During the production of aluminium oxide using the Bayer process, each tonne of alumina results in 360-800 kg of red mud as a residue. It contains minerals, such as the oxides of silicon, iron and titanium, together with residual alkali content. This alkali results from residues of caustic soda, which is used in the digestion process. Although as much caustic soda as possible is separated from the red mud, and returned to the Bayer process, a small residual amount remains. Apart from the alkaline residues, the red mud does not contain anything else that has been added during the process and is thus not classified as hazardous waste. It is disposed of in a safe manner. The red coloration results from the iron content. Red mud A pre-treatment (e.g. with gypsum) is first used to lower the pH of the red mud. The landfill sites used are sealed to make sure that alkaline constituents cannot find their way into the groundwater, and the effectiveness of the seal is monitored continually. Once a waste-disposal site has reached the limit of its capacity Red mud disposal site and the red mud covered over with layers of ash, sand or topsoil, it can be rehabilitated using suitable grasses and trees. It is also possible to rehabilitate the site using selected grasses without covering it over. Although rehabilitation measures take years, they do enable the landscape to be returned to something very much like its original form. In addition, profitable uses have also been found for red mud, for instance as a dye for bricks or as a filler material in road building. This can clearly reduce the amount of material sent to landfill sites. ‐ 26 ‐ Rehabilitation of a red mud disposal 6.1.2.2 Emission An important objective is to reduce emissions and pollutants at every stage in the extraction and processing of aluminium. The first measure adopted here is to ensure that the energy needed for fused-salt electrolysis is obtained as far as possible from hydroelectric power in order to reduce the emission of pollutants, such as CO2, by the combustion of fossil fuels. This stage of the production is thus usually carried out where there is ready access to cheap electricity in the form of hydroelectric power. Over the last 30 years, emissions of fluorides, which are formed in the electrolytic bath by decomposition of the cryolite flux, have been reduced to less than a third by further developments in pot technology. Modern extraction plants remove some 99% of the fluorides emitted and return them to the pots. Major efforts have also been devoted to reducing greenhouse gases. One is mainly concerned here with per fluorinated hydrocarbons (PFCs), which can form if the fluoride produced from cryolite during the electrolysis process reacts with the carbon of the anode (anode effect). Between 1980 and 2003, the industry managed to reduce the formation of PFCs during the production of primary aluminium by approximately 40% worldwide; further major efforts are still in progress to reduce this still further in future. The aluminium industry has signed voluntary commitments to reduce emissions in many countries. The industry is trying to reduce emissions of PFCs amongst other things by developing the technology of the alumina-reduction cells still further. Any reduction in the occurrence of the anode effect also means a simultaneous reduction in energy consumption. Research is also currently being undertaken on alternatives to the use of carbon anodes. This could eliminate the formation of PFCs completely. In the last 20 years, emissions of carbon dioxide (CO2), which is formed during electrolysis by combustion of the anode, have also been reduced by over 10% by reducing the amount of anode paste used. Further reductions can be expected as a result of optimization of the process efficiency. Generally speaking, CO2 emissions by the aluminium industry are only about 2% of the emissions that result from private transport. All pollutants and dust particles from the electrolysis process are collected directly in the alumina-reduction cell by bringing the waste gases into contact with alumina in a reactor (dry absorption); the dust- and pollutant-laden alumina is first separated out in a filter and then returned to the electrolysis process. 6.1.2.3 Energy The major part of the energy consumed by the aluminium industry is used in the production of primary aluminium. On a worldwide basis, 55% of this energy is provided by hydroelectric power. As the conditions for the use of hydroelectric power are often best in sparsely populated areas, the energy can be utilized directly in the immediate vicinity to produce aluminium without having to transport it over larger distances. Instead, the energy is stored directly in the aluminium produced, where it remains even if the aluminium is recycled. Optimization of the extraction process has already led to a significant reduction in the energy consumed during the production of primary aluminium. In the last few decades it has been reduced by over 30%. ‐ 27 ‐ The remelting of aluminium during recycling only requires 5% of the energy that is needed to produce the same quantity of primary aluminium. In the last few decades, process optimization has also led to a reduction in this requirement by over 25%. Secondary aluminium’s continually increasing share of total aluminium production is thus making a significant contribution to saving energy. Hydro-electric power plant 6.1.3 Aluminium Processing 6.1.3.1 Residual Products and Emission Recycling, or the reuse of the metal and operating materials, is an important principle of sustainability in the aluminium industry. It is not limited to aluminium recycling in the narrowest sense and in aluminium processing it includes more than just the metal itself. As part of the endeavour to conserve resources and establish in-house closed production loops, both scrap, such as foil, casting and profile residues, and particularly operating and auxiliary materials are reused again and again as far as possible. For example, core sand in sand casting, rolling oils in the manufacture of semi-finished products and solvent residues from coating processes are always reused within the plant. Not only do such in-house recycling loops conserve resources, they also reduce the burden on landfill sites. The general principle is to avoid waste and residues whenever possible, and where this is not possible, to place minimum demands on waste-disposal sites. Possible emissions produced during processing are oil mist in rolling mills, solvent vapors during fabricating and sprays for dies in foundries. These are collected and returned to the production process. Noise is also an emission in the widest sense; during aluminium processing, this occurs for example when profiles are cut to length. Noise emissions can be reduced to a large extent by use of suitable shielding. 6.1.3.2 Energy The energy needed during the processing of aluminium is to a very large extent the electrical energy needed to drive the processing equipment and, where necessary, the thermal energy for heat treatment. Compared with the production of primary aluminium, especially fused-salt electrolysis, which accounts for three-quarters of the energy requirement, processing is far less energy intensive. The precise energy consumption during processing is, of course, strongly dependent on the type of product, the equipment used and the production steps involved. ‐ 28 ‐ 6.1.4 Aluminium Products When it comes to their practical use, aluminium products offer some diverse ecological benefits. For example, aluminium components have a relatively long life and thus rarely have to be replaced, thereby saving both energy and resources. The energy used to produce aluminium initially thus pays off in the long term. In addition, improving the corrosion resistance can extend the life of a product. When a component has reached Aluminium beverage cans the end of its useful life, it can be recycled and thereby reprocessed using only a fraction of the energy initially required to extract the aluminium, and without any loss in quality. When aluminium is used as a packaging material in the food industry, its total barrier property and opaqueness improve the shelf life of food and markedly reduce product losses as a result of deterioration; this also results in waste being minimized. Particularly in the transport sector, aluminium products have the advantage that they can help save energy because of their lightness. The reduction in weight of a vehicle or a carriage of an underground train, for example, leads to a significant reduction in the consumption of fuel or electricity, as well as the corresponding emissions where applicable. This makes sense both ecologically as well as economically. Here, there is a rapid payback on the energy needed to make the aluminium product because weight savings of up to 40% allow large energy savings to be made, especially in vehicles used for local public transport that have to start up and stop frequently. If an aluminium vehicle is used a lot, these energy savings can exceed the extra energy required to produce the vehicle within a relatively short period. Rail carriages made from aluminium From an environmental point of view, the main benefit of aluminium products is generally their recyclability. Not only does recycling of used aluminium conserve resources and save energy, it also significantly reduces waste. 6.1.5 Aluminium Recycling The fact that aluminium can be recycled any number of times and practically without any loss in value is without doubt the main ecological argument for using it. The recycling of used products requires only 5% of the energy needed to produce the same quantity of primary aluminium. Not only does this conserve raw materials (in particular bauxite), it also results in significantly less waste, residues and emissions. The reuse of aluminium is after all at the heart of recycling, the basic principle of sustainability in the aluminium industry: after it has been used, the metal is returned to the material loop – a process that can be repeated an almost unlimited number of times. ‐ 29 ‐ You will find more detailed information on this subject in the chapter about recycling. ‐ 30 ‐ 7.0 Uses Packaging has replaced the building and construction industry as the largest consumer of aluminium in the United States because aluminium is impermeable to gas, resistant to corrosion, and recyclable. The most prominent has been the use of aluminium for beer and carbonated beverages. Over 95% of the beer and carbonated soft drinks are packaged in two-piece aluminium cans. Alloys 3004 and 5128 are used for can bodies and ends, respectively. Aluminium has long dominated the market for short, convenience-type cans with easy-open lids, which contain foods such as meat, pudding, and fish; and it is beginning to make headway into the market for larger food cans(e.g., pet food cans). The following uses for aluminium are gathered from a number of sources as well as from anecdotal comments. I'd be delighted to receive corrections as well as additional referenced uses. • • • • • • • • cans and foils kitchen utensils outside building decoration industrial applications where a strong, light, easily constructed material is needed although its electrical conductivity is only about 60% that of copper per area of cross section, it is used in electrical transmission lines because of its lightness and price alloys are of vital importance in the construction of modern aircraft and rockets Aluminium, evaporated in a vacuum, forms a highly reflective coating for both visible light and radiant heat. These coatings soon form a thin layer of the protective oxide and do not deteriorate as do silver coatings. These coatings are used for telescope mirrors, decorative paper, packages, toys, and in many other uses The oxide, alumina, occurs naturally as ruby, sapphire, corundum, and emery, and is used in glass making and refractories. Synthetic ruby and sapphire are used in the construction of lasers [16, 10] ‐ 31 ‐ 8.0 Health and Safety 8.1 Aluminium in the human body On average the human body contains estimated 35 mg aluminium. This is distributed as follows: about 50% is in the lung tissue, 25% in soft body parts and a further 25% in the bones. As a trace element, aluminium is thus a natural component of our bodies. We take up 2-6 mg aluminium a day on average in the form of compounds via food or breathing; the figure for drinking water is less than 0.1 mg. Under normal circumstances, the aluminium intake from cooking utensils or packaging materials is equivalent to less than 3% of the total daily intake. Over 99% of this quantity is discharged again as excrement; the rest enters the bloodstream from where it is filtered out by the kidneys into the urine. Like most other substances in the human body that need to be prevented from reaching the brain, the aluminium present in the bloodstream is kept away from the brain via a so-called ‘blood–brain barrier’ (which regulates material transfer between the bloodstream and the nerve centre). The fact that limited quantities of aluminium in the body are harmless has also been confirmed by the results of research work: scientists fed volunteers food whose aluminium content was a factor 100 higher than the normal average value for the test persons and there was no evidence of any damage to their health. In the past, much larger quantities have been fed to animals in tests; even under these conditions practically all of the aluminium is passed through the gastrointestinal tract and discharged. We all come into contact with aluminium in one of its various forms every day. Without doubt the best known is as a metal, which forms the basis for many of the consumer goods we use daily. However, we also come into contact with it in other ways. Aluminium is always present in nature combined chemically with other materials, i.e. in non-metallic form. Overall, it is the third most common element in the earth’s crust. It is part of almost all rocks and soils. As a result of soil erosion, aluminium compounds in the form of dust particles find their way into the atmosphere or are dissolved in water and thus taken up by plants and animals, and also reach human beings via the food chain. The uptake of such aluminium compounds has been taking place since the beginnings of the human race and poses absolutely no health risk. Aluminium is also present as a natural trace element in the human body. In addition, nonmetallic aluminium compounds can be beneficial to health by forming the basis for certain forms of medication. We also come into contact with them as food additives. Aluminium sulphate has become the yardstick for drinking-water treatment worldwide. It is fairly safe to handle, economical to produce and poses no toxicological risk. 8.2 Aluminium in medicine Doctors have been prescribing aluminium-based preparations for their patients on a large scale for a good many years. Even larger quantities of non-prescription medication containing aluminium compounds have also been taken and there has been no health risk involved. ‐ 32 ‐ The most widely used compound is aluminium hydroxide. It is used as an antacid for the treatment of gastric ulcers and as a phosphate buffer in cases of chronic renal deficiency. Aluminium compounds neutralise excess acidity in a particularly effective and safe manner. As long as there is no severe impairment of the renal function, there is also no contraindication and no undesirable side effects are expected. In several studies, the intake of large quantities of aluminium hydroxide for acid binding was investigated in comparison to control groups without any negative effects being observed. In addition, one also finds aluminium compounds in deodorants, disinfectants and in carriers for serum injections. Damaging effects caused by aluminium can also be ruled out here. 8.2.1 Dialysis After years of treatment, dialysis patients (patients with an impaired renal function who regularly have to undergo blood purification) often develop brain dysfunctions, bone brittleness and amyosthenia. The cause of this dialysis encephalopathy (which is not linked to tissue changes in the brain) is aluminium-containing medication, via which there is an uptake of up to 200 mg aluminium a day. The medication is intended to precipitate out dietary phosphates in the intestines so that these do not overload the body, which is no longer capable of separating these out via the kidneys. Nowadays, the aluminium content in the blood of all dialysis patients is carefully monitored continually, and the medical profession is trying to develop medication that does not cause aluminium to enter the bloodstream. 8.2.2 Alzheimer’s disease All over the world, most waterworks use aluminium sulphate as a flocculent to provide drinking water. Flocculants are used in drinking-water treatment to tie up small inorganic particles and bacteria present in the water and to filter them out. While some waterworks can manage without this treatment, there are others whose water is so turbid (because of a high content of natural substances or germs) that it would be undrinkable without treatment. According to a World Health Organization (WHO) guideline, the current maximum permitted level of aluminium in drinking water is 0.2 mg total aluminium per liter. This value has mostly been determined on the basis of taste and aesthetics, and the WHO has given no health-relevant criteria for determining the maximum aluminium content in drinking water. In actual fact, only 0.5-1% of a person’s required daily aluminium intake comes from drinking water. Aluminium sulphate has become the yardstick for drinking-water treatment worldwide. It is fairly safe to handle, economical to produce and poses no toxicological risk.[1] 8.3 Food and packaging Aluminium is used in many different ways in the preparation, protection and storage of food and drink. It is an extremely good conductor of heat and makes very efficient use of energy when preparing and serving both cold and hot dishes. In addition, aluminium is very light. This reduces transport costs and makes aluminium the ideal material for use in packaging where weight is important. In addition, its excellent barrier properties prevent the ingress of micro-organisms, air and light. This property in particular is very important because studies have shown that up to 30% ‐ 33 ‐ of the product quality of food depends on the packaging. Aluminium is ideally suited for preventing deterioration in the quality of contents. It does not pose a health risk or have any effect on the taste of the food, and it is also effective in preventing the ingress of other aromas. Aluminium’s natural oxide layer ensures that the metal behaves fully in a chemically stable manner and does not react in any way with the packaged food. In addition, beverage cans and food cans have a protective film of lacquer on the inside and this ensures that the acids and salts in the food and drink do not come into contact with the metal. Aluminium has a whole range of properties that make it an ideal packaging material: in addition to its light weight and excellent barrier properties, these include primarily its good malleability while still maintaining good shape-retaining properties, its high reflectance for light and UV rays, its corrosion resistance and, of course, its complete recyclability. As mentioned in the Aluminium in the environment chapter, aluminium is present in a nonmetallic form, i.e. chemically combined with other substances, everywhere in nature. It is therefore not surprising that most foodstuffs already contain some aluminium naturally. Tea and certain types of spice are typical examples of foodstuffs with high aluminium concentrations. Aluminium compounds are also used in the industrial-scale processing of food. For example, they are used as carriers for food colorants or as separating agents for milk powder. When it comes to such aluminium compounds, one is not dealing with aluminium in metallic form, of course, but as a chemical element combined with other substances. Even so, there is absolutely no health risk associated with such additives even at higher doses. From time to time concern is expressed about aluminium being taken up by the body from food and drink prepared using aluminium pans, containers or other aluminium-containing kitchen utensils. In fact, the uptake of aluminium by the body in this way is negligible and does not pose any risk to health whatsoever. By far the largest share of the 5-12 mg aluminium that an average person takes in daily with his or her food comes from natural sources. As aluminium is omnipresent in nature, mankind has come into contact with it via food or the environment since time immemorial. ‐ 34 ‐ 9.0 Recycling 9.1 Recycling of Aluminium The term ‘recycling’ means the general reuse of products that have reached the end of their useful life to make new ones. Recycling is carried out on a large scale in the aluminium industry, too, and thus makes an important contribution to the protection of the environment. Aluminium has been recycled since the metal first started to be produced on a commercial scale at the beginning of the 20th century. Since then, a large number of secondary-aluminium smelters (or secondary refiners as they are also called) have been established; Using new scrap or used scrap, these supply the usual formats for further processing (such as ingots or billets), deoxidants for the steel industry and casting alloys. The recycling process comprises the following steps: 1. Collection 2. Pre-treatment of the scrap 3.Melting 4.Refining 5.Casting to shape Aluminium cans Using modern technology, aluminium can be remelted without any loss in quality and then recast. In addition, because of aluminium’s high intrinsic metal value, recycling is economically attractive. Recycling of aluminium conserves raw materials and energy and reduces the amount of space needed for landfill sites. The economic interest in recycled aluminium can be seen in the diagram below, which shows production figures for primary and secondary aluminium for the period 2000 to 2003. The production of secondary aluminium shows growth. Figure 11: Aluminium production 2000-2003 ‐ 35 ‐ 9.2 Types of Scrap The aluminium recycling industry processes different forms of aluminium scrap. New scrap (or process scrap) is the term used to describe the aluminium scrap produced during the manufacture and fabrication of aluminium alloys until such a time as the products are sold to the end-user. (This is shown in the figure below using extruded and forged components as an example.) Most new scrap originates from fabricators, so the composition of the alloys is well documented. This scrap is usually free from contamination. Some new scrap is, however, coated or greased and has to be pre-treated before remelting. New scrap Old scrap (or used scrap) is recovered from used end-products and aluminium components. An efficient network of scrap-metal dealers collects and sorts aluminium scrap from the building and construction industry and from end-of-life vehicles, electrical equipment, machinery, printing plates, household goods, used drinks cans, etc. Figure 12: New scrap from the production process [19] ‐ 36 ‐ References [1] Othmer- Kirk, Encyclopedia of Chemical Technology (1980) V-2- , PP (129-185) [2] Othmer-Kirk, Concave Encyclopedia of Chemical Technology (1980), PP (75-81) [3] M.Considine- Douglas, Chemical and Process Technology Encyclopedia (1984), PP (76-87) [4] Gerharts-Wolfganf, Ullman’s Encyclopedia of Industrial Chemistry (1980) V-1-, PP (459-478), (481-525) [5] Journal of Chemical Technology and Biotechnology, V-57, 58-Number -2, 3-, PP (137), (247) [6] http://en.wikipedia.org/wiki/aluminium [7] http://www.webelements.com/webelements/elements/text/Al/key.html [8] http://environmentalchemistry.com/yogi/periodic/Al.html [9] http://mysite.du.edu/~jcalvert/phys/alumin.html [10] http://sam.davyson.com/as/physics/aluminium/site/uses.html [11] http://www.world-aluminium.org/?pg=140 [12] http://www.laputanlogic.com/articles/2005/03/007-0001-7813.html [13] http://www.explainthatstuff.com/aluminum.html [14] http://scifun.chem.wisc.edu/chemweek/aluminum/aluminum.html [15] http://www.chemheritage.org/pubs/ch-v25n4-articles/feature_alum_p1.html [16] http://www.greener-industry.org/pages/aluminium/aluminium_4PMsummary.html [17] Aluminium-Verlag, Aluminium Handbook [18] http://www.msm.cam.ac.uk/phase-trans/abstracts/M7-8.html [19] Aluminium-Taschenbuch [20] http://www.world-aluminum.org/production/refining/chemistry.html [21] http://www.rocksandminerals.com/aluminum/process.htm [22] http://electrochem.cwru.edu/ed/encycl/art-a01-al-prod.htm [23] Sezgin, Tarhan Outside Market Research ‐ 37 ‐ Appendix ALUMINUM, PRIMARY: WORLD PRODUCTION, BY COUNTRY1, 2 (Thousand metric tons) Country Argentina Australia Bahrain Bosnia and Herzegovinae, 4 Brazil Cameroon Canada Chinae Croatia4 Egypt France Germany Ghana Greece Hungary Iceland5 India6 Indonesiae, 6 Iran Italy Japan7 Mexico6 Mozambique Netherlands New Zealand Nigeriae Norway Poland8 Romania9 Russia Serbia and Montenegro4 Slovakia6 Slovenia4 South Africa Spain Surinamee Sweden Switzerland Tajikistan 1999 206 1,718 503 70 1,250 90 2,390 2,530 14 193 455 634 104 170 34 220 614 106 137 187 11 63 ‐‐ 286 327 16 1,020 51 174 3,146 73 109 77 689 364 6 99 34 229 2000 262 1,769 509 95 1,277 r 86 r 2,373 2,800 15 r 193 441 644 137 r 168 34 224 644 160 140 e 189 7 61 54 302 328 ‐‐ 1,026 47 179 3,245 88 110 84 r 673 366 ‐‐ 101 36 r 269 r ‐ 38 ‐ 2001 245 e 1,797 r 523 r 96 1,140 r 91 r 2,583 3,250 16 r 189 e 462 652 144 r 166 r 34 r, e 243 624 180 160 r 187 7 52 266 294 322 ‐‐ 1,068 45 182 3,300 100 110 e 77 r 662 376 ‐‐ 102 36 r 289 2002 269 r 1,836 519 r 104 1,318 80 e 2,709 4,300 ‐‐ r 190 e 463 r 653 r 117 r 165 35 e 264 671 r 160 169 r 190 r 6 r 39 r 273 284 r 335 e ‐‐ 1,096 51 r, e 187 r 3,347 112 r 112 e 88 707 r 380 ‐‐ 101 40 r 308 2003e 272 p 1,857 3 525 3 105 1,381 3 80 2,792 3 5,450 ‐‐ 190 450 650 13 165 35 260 790 180 170 190 7 ‐‐ 408 3 300 340 ‐‐ 1,150 50 190 3,478 3 115 115 85 738 3 385 ‐‐ 101 40 319 3 62 61 62 r, 3 63 r 63 Turkeye 9 r Ukraine 115 104 106 112 114 3 United Arab Emirates,Dubaie 440 470 500 536 540 r United Kingdom 272 305 341 344 325 United States 3,779 3,668 2,637 2,707 2,703 3 Venezuela 570 571 r 571 605 r 601 3 TOTAL 23,600 24,300 r 24,300 26,000 r 27,700 e Estimated. pPreliminary. rRevised. ‐‐ Zero. 1 World totals and estimated data are rounded to no more than three significant digits; may not add to totals shown. 2 Primary aluminum is defined as "the weight of liquid aluminum as tapped from pots, excluding the weight of any alloying materials as well as that of any metal produced from either returned scrap or remelted materials." International reporting practices vary from country to country, some nations conforming to the foregoing definition and others using different definitions. For those countries for which a different definition is given specifically in the source publication, that definition is provided in this table by footnote. Table includes data available through May 10, 2004. 3 Reported figure. 4 Primary ingot plus secondary ingot. 5 Ingot and rolling billet production. 6 Primary ingot. 7 Excludes high purity aluminum containing 99.995% or more as follows, in metric tons: 1999‐‐34,893; 2000‐‐40,956; 2001‐‐26,586; 2002‐‐40,443 (revised); and 2003‐‐40,000 (estimated). 8 Primary unalloyed ingot plus secondary unalloyed ingot. 9 Primary unalloyed metal plus primary alloyed metal, thus including weight of alloying material. ‐ 39 ‐ ...
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This note was uploaded on 02/24/2010 for the course CHEMENG CHE 117 taught by Professor Özcanbeşergil during the Spring '08 term at Ege Üniversitesi.

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