Dissolution Kinetic And Solvent Extraction Of Aluminium From Kaolin

1.3.2 Recycling of aluminium

Aliminium is theoretically 100% recyclable without any loss of its natural qualities. According to the international resources panel’s metal stocks in society report, the global per capital stock of aluminum in use in society (i.e. in cars, building, electronic etc) is 80kg, much of this is in more-developed countries (350-500kg per capital) rather than less-developed countries (35kg per capital0 knowing the per capital stocks and their approximate life span is important for planning recycling. Recovery of the metal via planning has become an important use of the aluminum industry. Recycling was a low-profile activity until the late 1960s, when the growing use of aluminium beverages cans brought it to the public awareness. Recycling involves melting the scrap, a process that requires only 50% of the energy used to produce aluminium from ore, through significant part (up to 15% of the input material) is lost as dress (ash-like oxides) [29], the dross can undergo a further [process to extract aluminum. In Europe aluminum experiences high rates of recycling, ranging form 42% if beverage cans, 85% of construction materials and 95% of transport vehicles [30].

Recycling aluminum is known as secondary aluminium, but maintains the same physical properties as primary aluminium. Secondary aluminium us produced in a wide range of formats and are employed in 80% of alloy injections. Another important use is for extrusion. White dross from primary aluminium production and form secondary recycling operation still contains quantities of aluminium that can be extracted industrially [31]. The process produced aluminium billets, together with highly complex waste materials. This waste releasing a mixture of gases (including, among others, hydrogen, acetylene and ammonia), which spontaneously ignites on contact with air, [31] contact with damp air result in the release of copious quantities of ammonia gas. Despite these difficulties, the waste has found use as filler in asphalt and concrete [32].

1.4 OCCURRENCE OF ALUMINIUM

In the earth’s crust, aluminium is the most abundant (8.3% by weight) metallic element and the third most abundant of all element (after oxygen and silicon) [23]. Because of its strong affinity to oxygen, it is almost never found in the elemental state; instead it is found in oxides or silicates. Feldspars, the most common groups if mineral in the earth’s crust, are aluminosilicates. Native aluminium metal can only be found as a minor phase in low oxygen fugacity environment, such as the interiors of certain volcanoes [34].

In the Northern Eastern continental slope of the south China sea and Chen et al [35] have proposed a theory of its origin as resulting by reduction from tetrahydroxoaluminate Al (OH)4- to metallic aluminium by bacteria [35].

It also occurs in the minerals Berl, Cryolite, garnet, spinel and turquoise. Impurities in Al2O3, such as chromium or iron yield the gemstone ruby sapphire, respectively. Although aluminium is an extremely common and widespread element, the common aluminium minerals are not economic sources of the metal. Almost all metallic aluminium is produced form the ore bauxide (AlOx (OH)3-2x). Bauxide occurs as a weathering product of low iron and silica bedrock in tropic climatic condition [36]. Large deposits of bauxite occur in Australia, Brazil, Guinea and Jamaica and the primary mining areas for the ore are in Australia, Brazil, China, India, Guinea, Indonesia, Jamaica, Russia and Suriname.

1.4.1 Production and Refinement of Aluminium

Aluminium forms strong chemical bonds with oxygen compared to most other metals, it is different to extract form ore, such as bauxite, due to the high reactivity of aluminium and the high reactivity of aluminium and the high melting point of most of the ores, for example, direct reduction with carbon, as is used to produce iron is not chemically possible because aluminium is a stronger reducing agent than carbon. Indirect carbon thermic reduction can be carried out using carbon and Al4C3, which forms an intermediate Al4C3 and this can further yield aluminium metal at a temperature of 1900-2000ËšC. This process is still under development, it requires less energy and yield less CO2 than the hall-herovit process, the major industrial process for aluminium extraction.[37] electrolytic smelting of alumina was originally cost-prohibitive in part of alumina, or aluminium oxide (about 2,000ËšC (3, 600Ëšf). Many minerals, however, will dissolve into a second already molten mineral, even if the temperature of the met is significantly lower than melting point of pure alumina without interfering in the smelting process in the Hall-Heroult process, alumina is first dissolved into molten cryolite with calcium fluoride and then electrolytically reduced to aluminium at a temperature between 950-980ËšC (1, 740 to 1, 800Ëšf) cryolite is a chemical compound of aluminium and sodium fluoride (Na3AlF6). Although cryolite is found as a mineral in Greenland, its synthetic form is used in the industry. The aluminium oxide itself is obtained by refining bauxite in the Bayer process.

The electrolytic process replaced the Wohler process, which involved the reduction of anhydrous aluminium chloride with potassium; both of the electrodes used in the electrolysis of aluminium oxide are carbon. Once the refined alumina is dissolved in the electrolyte, it disassociates and its ions are free to move around. The reaction at the cathode is:

                                         Al3+ + 3e → Al                                             (5)

Here the aluminium ion is being educed. The aluminium metal then sinks to the bottom and is tapped off, usually cast into large blocks called aluminum billets for further processing.

At the anode, oxygen is formed:

                                    202- → 02 + 4e                                                     (6)

To some extend, the carbon anode is consumed by subsequent reaction with oxygen to form carbon dioxides, the anodes in a reduction cell must therefore be replaced regularly. Since they are consumed in the process the cathodes do erode, mainly due to electrochemical process and metal movement. The Hall-heroult process produce aluminium with a purity of above 99% further purification can be done by the hooped process. The process involves the electrolysis of molten aluminium with sodium, barium ad aluminium fluoride of 99.99% [38, 39]. Electric power represents about 20% to 40% of the cost of producing aluminium, depending on the location of the smelter. Aluminium production consumes roughly 5% of electricity generated in the US [40]. Smelters tend to be situated were electric power is both plentiful and inexpensive, such as the United Arab Emirates with excess natural gas supplies and Ireland and Norway with energy generated form renewable sources. The world’s largest smelters of alumina are People’s Republic of China, Russia and Quebec and British Columbia in Canada [40, 41, 42].

1.4.2 Compound and halides of aluminium

Aluminum has oxidation states of +1, +2, +3 oxidation state +3. The vast majority of compounds, including all containing minerals and all commercially significant aluminium compound, feature aluminium in the oxidation state 3+, the coordination number of such compounds varies, but generally Al3+ is six-coordinate of tetracoordinate. Almost all compounds of aluminium (III) are colourless [33]. 

Oxidation states +1 and +2

Although the great majority of aluminium compounds features Al3+ centres, compounds with lower oxidation states are known and sometime of significant as precursors to the Al3+ species. Aluminium forms one stable oxide known by its mineral name corundum sapphire and ruby are impure corundum contaminated with trace amounts of other metals. The two oxide-hydroxides, Al0 (OH), are biochmite and diasphore. There are three trohydroxides: bayerite, gibbsite, and nordstrandite, which differ in their crystalline structure (polymorphs). Most are produced from ores by a variety of wet process using acid and base. Heating the hydroxide leads to formation of corundum. These materials are of central importance to the production of aluminium and are themselves extremely useful.

Aluminium (I)

AlF, AlCl, and AlBr exist in the gaseous phase when the trihalide is heated with aluminium. The composition AlI is unstable at room temperature with respect to the trilodide [43].

                         3AlI →AlI3 + 2Al                                      (7)

A stable derivative aluminium monoiodile is the cyclic addict formed with triethylamine, Al4I4(NEt3)4. Also the theoretical interests but only of fleeting existence are Al2O and Al2S. Al20 is made by heating the normal oxide, Al2O3, with silicon at 1, 800ËšC (3, 272Ëšf) in a vacuum. [43] Such materials quickly disproportionate to the starting materials.

Aluminium II

Al (II) compound are invoked or observed in the reactions of Al metal with oxidants for example aluminium monoxide, AlO, has been detected in the gas phase after explosion [44] ad in stellar absorption spectra. [45] More thoroughly investigated are compounds of the formula R4 Al2 where R is a large organic ligard [46]

Halides  

All four trihalides are well known, unlike the structure of the three heavier trihalides, aluminium fluoride (AlF3) features six-coordinate Al. the octahedral coordination environment for AlF3 is related to the compactness of fluoride ion, six of which can fit around the small A3+ centre. Alf3 sublimes (with crackling) at 1, 291ËšC (2, 356Ëšf). With heavier halides, the coordination numbers are lower; the odder trihalides are diametric or polymeric with tetrahedral Al centers. These materials are prepared by treating aluminium metal with the halogen, although other methods exist. Acidification of the oxides or hydroxide affords hydrates. In aqueous solutions the halides often form mixtures, generally containing six-coordinate Al centers, which are features both halide and aquo ligands. When aluminium ad fluoride are together in aqueous solution, they readily form complex ions such as (AlF (H20)5] 2+, AlF3 (H20)3 and [AlF6]3-. In the case of chloride, polyaluminium dusters are formed such as [Al1304 (OH) 24 (H20)12 ]7+

1.5 APPLICATION OF ALUMINIUM

Aluminium is the most widely used non ferrous metal [47] Global production of aluminium in 2005 was 31.9million tones. It exceeded that of any other metal except iron (837.5 million tones). [48] Forecast for 2012 is 42-45 million tones, driven by rising Chinese output, aluminum is almost always alloyed, which markedly improves its mechanical properties, especially when and beverages cans are alloys of 92% to 99% aluminium [49]. The main alloying agents are copper; Zinc, Magnesium, Manganese, and Silicon (e.g. duralumin) and the levels of these other metals are in the range of a few percent by weight [50]. Some of the many uses for aluminium metals are in:

• Transportation (automobiles, aircraft trucks, railway, cars, marine vessels, bicycles etc) as sheet, tube casting etc.

• Packaging (cans, foil etc)

• Construction (windows,  doors, siding, building wire etc [51]

• Wide range of household items from cooking utensils to base hall bats watch [51]

• Street lighting poles, sailing ship, masks, walking pole etc.

• Outer shells of consumer electronics, also cases for equipment.

• Electrical transmission lines of power distribution.

• MKM Steel and Alnico magnets.

• Super purity aluminium (SPA, 99.980% + 99.999% Al) used in electronics and CDs.

• Heat sinks for electronic appliances such as transistors and CPUs.

• Subtract material of metal-core copper clad laminates used in high brightness LED lighting

• Powdered aluminium is used in paint in pyrotechnics such as solid rocket fuels and thermite.

• Aluminium can be reacted with hydrochloric acid or with sodium hydroxide to produce hydrogen gas.

• A variety of countries including France, Italy, Poland, Finland, Romania, Israel, and the former Yugoslavia, have issued coins alloys [52].

• Some guitar models sport aluminium diamond places on the surface of the instruments, usually either chronic or black. Kramer guitars and Travis Bean are both known for having produced guitars with necks made of aluminium which gives the instrument a very distinct sound.

1.5.1 History of aluminium

The ancient Greeks and Romans used alum in medicine as an astringent and in dyeing processes. In 1961 de Morveall proposed the name “Alumine” for the base in alum. In 1807, Davy proposed the name aluminium for the mental undiscovered at that time, and later agreed to change it to aluminium shortly thereafter; the name aluminium was adopted by IUPAC to conform to the “Lum” ending of most element. Aluminium is the IUPAC spelling and therefore the international standard. Aluminum was also the accepted spelling in the USA until 1925, at which time the American chemical society decided to revert lack to aluminium, and to this day Americans still refers to aluminium as “aluminum”. Aluminium is one of the elements which was alum or alumen, KAL(S04)2, has an alchemical symbols, (the symbol to the right shows schede’s symbol, alchemy is an ancient pursuit concerned with, for instance, the transformation of other metals into gold).

Aluminium was first isolated by Hans Christian’s oersted in 1825 that reacted aluminium chloride (AlCl3) with potassium amalgam (an alloy of potassium and mercury). Heating the resulting aluminium amalgam under reduced pressure caused the mercy to boil away leaving an impure sample of aluminium metal.