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CHAPTER ONE

• INTRODUCTION
  • Kaolinite

Kaolinite is one of the rare earth compounds that contain high concentration or percent of alumina and silica in the earth crust, and it has the chemical composition Al₂Si₂O₅(OH)₄. Rare earth (RE) compounds are “hi-tech” materials used in electronics automotive catalytic converter, glass/ceramic permanent magnets and nuclear energy. High demand/tight supply issues prompt the need for intensive research in the field of rare earth recovery/purification, with emphasis on development of new sources to secure sustainable access to supply in the future. Due to the abundance of Kaolinite in the superficial layers in nature, high specific surface area for adsorption and relatives ease of mining/processing [1].The Kaolinite or rare earths are leached and we can recover high purity and product by solvent extraction.

In April 2008, the US Naval medical research institute announced the successful use of a Kaolinite derived aluminosilicate nonoparticles infusion in traditional gauze, known commercially as Quick clot combat Gauze [2]. The purpose of this study is to explain the geochemical principles that govern acid chloride aluminum leaching and to provide a basis for understanding the testing application of acid leaching to the undeveloped resources base [3].

Kaolinite is a clay mineral, part of the group of industrial minerals, with the chemical composition Al₂Si₂O₅(OH)₄. It is a layered silicate mineral with one tetrahedral sheet linked through oxygen atoms to one octahedral sheet of alumina Octahedral [4]. Rocks that are rich in Kaolinite are known as Kaolin or china clay [5]. The name is derived from kao-ling (Chinese word: gaoling) a village near Jingdezhen jlangxi province, china [6]. The name entered English in 1727 from the French version of word “Kaolin” following François Xavier d Entrecolles’s reports form Jindgezhen [7]. In Africa, kaolin is sometimes known as Kalaba (in Gabon [8] and Cameroon [9]) Calaba and calaba chop (in Equatorial Guinea).

Kaolinite has a low shrink-swell capacity and a low cation exchange capacity (1-15meg/100g), it is a soft, earthy, usually white mineral (dioctahedral phyllosilicate clay), produced by the chemical weathering of aluminum silicate minerals like feldspar. In many parts of the world, it is colored pink-orange-red by iron oxide, giving it distinct rust, lighter concentrations yield white, yellow or light orange colour. Alternatively layers are sometimes found as at providence canyon state park in Georgia, ssssUnited State commercial grades of kaolin are supplied and transported as dry powder, semi-dry noodle or as liquid slurry.

• Source of Kaolinite

Kaolinite or kaolin mineral has its name derived form Gaoling (kao-ling) which is a high hill in the Jindgenzhen, Jiangxl province of china, although it was mined in that Chinese province, the mineral was first described as mineral species in Brazil in the year 1867. Kaolinite is mined as kaolin. Brazil, United Kingdom, Germany, India, Korea, France, China, and the Untied State of America are some of the known countries on which premium Kaolin clay is sourced. The mineral is typically found abundant in soils that are found o chemical weathering of rocks and have hot and moist climate such as tropical rainforest areas. In comparison along a gradient that leads towards progressively cooler or drier climate, the proportion of Kaolinite decreased while other clay minerals such as illite and smectite which are formed in cool and dry climates increase. The climatic factors in the formation of Kaolinite tell soil much of the mineral’s relation to its sources areas geologic history. [8]. Kaolin clay is included in the group of hydrous aluminum silicates, healing stones kyanite and dumortierite are aluminum silicate. Aluminum is also found in the healing stone sapphire, amethyst, heliotrope (bloodstone), ruby, anyolite, emerald, idocrase, rhodonite, tiger iron, green tourmaline, alexandrite and moldavite. The kaolin mineral group includes other common clay mineral such as dickite, halloysite, nacrtie, Kaolinite and allophone. The kaolin mineral group is usually found in sediments, soils, hydrothermal deposits and sedimentary rocks. It takes the bulk of the mineral that are formed in the pouter crust of the earth at a wide range of geologic environment. Many of these silicates are of economic importance. Most of them are used ion various industries, the clay minerals that form the main constituent of kaolin are commonly formed through the cycles of rock formation. Although it may share the same chemical composition with their clay minerals in its group, it differs in its optical or physical properties [8].

• Uses of Kaolinite

The largest use is in the production of paper, including ensuring the gloss on some grades of paper. Kaolin is or was used:

• Ceramic: It is generally the main component in porcelain.
• In toothpaste
• As a light diffusing material in white incandescent light bulbs.
• In cosmetic
• As paint to extend titanium dioxide (Ti0₂) and modify gloss levels.
• For its semi-reinforcing properties in rubber.
• In adhesives to modify rheology [9]
• The production of common smoking pipes in Europe and Asia.
• In organic farming as spray applied to crops to determine insect damage, and in the case of apples to prevent sun scald.
• As whitewash in traditional stone masonry homes in Napal. The most common method is to paint the upper part with white kaolin clay and the middle with red clay. The red clay many extend to the bottom or the bottom may be painted black.
• As a filler in Edision diamond discs [10].
• As an indicator in radiological dating since Kaolinite can contain very small traces of uranium and thorium.
• To soot an upset stomach, similar to the way parrots (and later, humans) in South American originally, used it [11].More recently, industrially produced Kaolinite preparations were formally common for treatment of diarrhea, the most common of these was kaopectate, which abandoned the use of kaolin in favour of attapulgite and then (in the United States) bismuth subsalicylate (the active ingredient in pepto-bismol).
• For facial mask or soap [12].
• Rubber/rubber industries: Kaolin is used as filler in rubber industries. They need a maximum of 0/002 percent of its manganese content and 0.001 percent for its calcium content.
• Paper coating industries: For the production of white and fine paper its whiteness is dominant for paper coating.
• Ceramic product: For the production of sanitary and table wares

Kaolin has many important applications and uses, kaolin used as filler, a suspending agent, extending agent and as a main continents. Because of its chemical composition, whiteness, particles size and other properties, kaolin is used as filler in the production of paints, rubber, paper and soap producing industries. Kaolin is eaten for health or to suppress hunger [13] a practice known as geophagy. Consumption is greater among women especially during pregnancy [14]. This practice has also been observed within a small population of African-American women in the Southern United State, especially Georgia [15]. There the kaolin is called white dirt, chalk or white clay chemistry of Kaolinite.

The chemical formula for Kaolinite as used in mineralogy is AL₂SI₂O₅ (OH₄) [16]. However, in ceramic applications the formula is typically written in terms of oxides, thus the formula, for Kaolinite is Al₂O₃.2SiO₂.2H₂O [17] cement chemist notation is even more tense: AS₂H₂, with the oxides represented as A=Al₂O₃, S=SI0₂. H=H₂0. Kaolinite group clays undergo a series in air at transformations upon thermal treatment in air at atmospheric pressure. Endothermic dehyxylation (or alternatively, dehydration) begins at 550-600˚c to produce disordered metkaolin, Al₂Si₂0₇, but continuously hydroxyl loss (-OH) s observed up to 900˚c and has been attributed to gradual oxolation of the metakaolin [18] because of historic disagreement concerning the nature of the metakaolin phase, extensive research has led to general consensus that metakaolin is not a simple mixture of amorphous silica (SIO₂) and Alumina (Al₂O₃), but rather a complex amorphous structure that retains some longer range order (but not strictly crystalline) due to stacking of its hexagonal layer [18].

2AL₂Si₂O₅ (OH)₄ →2Al₂Si₂0₇ + 4H₂0                         (1)

Further heating to 925-950⁰c converts metakaolin to an aluminum silicon spinal Si₃Al₄O₁₂, which is sometimes also referred to as gamma-alumina type structure.

2AL₂Si₂O₇ →SiAL₄ 0₁₂ + SiO₂                                                   (2)

Upon calcinations to ˜1050˚c, the spinal phase (S1₃ Al₄ O₁₂) nucleates and transforms to mullite, 3A_l2 O₃.2SiO₂, and highly crystalline cristobalite, SiO₂

3Si₃ Al₄ O₁₂ → 2Si2 Al₆ O₁₃ + 5SiO₂                                          (3)

• OCCURRENCE OF KAOLINITE

Kaolinite is one of the most common mineral; it is mined as kaolin, in Vietnam, Brazil, Bulgaria, France, United Kingdom, Iron, Germany, India, Australia, Korea, the people’s republic of China, the Czech republic and the United State [19]. Kaolinite clay occurs in abundance in soils that have formed form the chemical weathering of rocks in hot-moist climates for example in tropical rainforest areas, comparing soils along a gradient towards progressively cooler of drier climates, the proportion of Kaolinite decrease while the properties of other, clay minerals such as illite (in cooler climate) or smeetite (in drier climate) increase, such climatically related differences in clay mineral content are often used to infer changes in climates in the geological past, where ancient soils have been buried and preserved [4].

In the institute national pour L΄Etude Agronomiqueau Congo Belge (INEAC) classification system, soils in which the clay fraction is predominantly Kaolinite are called kaolisol (from kaolin and soil) [20]. In the US the main kaolin deposits are found in central Georgia, on a stretch of geological fall line between August and Macon. The deposits were formed between the late cretaceous an dearly paleogene, about 100 million to 45 million years ago, in sediments derived from weathering igneous and metamorphic rocks [21] kaolin production in the US during 2011 was 5.5 millions tones [16].

• ALUMINIUM

Aluminum (or aluminum) is a chemical element in the boron group with symbol Al and atomic number 13, it is silvery white, and it is not soluble in water under normal circumstance. Aluminums is the third most abundant element (after oxygen and silicon), and the most abundant metal, in the earth crust, it makes up about 8% by weight of the earth’s solid surface. Aluminium metal is so chemically reactive that native specimens are rare and limited to extreme reducing environments instead, it is found combined in over 270 different minerals [22]. The chief or of aluminium is bauxite. Aluminium is remarkable for the metal’s low density and for its ability to resist corrosion due to the phenomenon of passivation. Structural component made from aluminums and its alloys are vital to the aerospace industry and are important in other areas of transportation and structural materials. The most useful compounds if aluminum, at least on a weight basis, are the oxides and sulfates. Despite its prevalence in the environment, aluminum salts are not known to be used by any form of life. In keeping with its pervasiveness, aluminums are well tolerated by plants and animals [23] owing to their prevalence, potential beneficial (or other wise) biological roles of aluminum compounds are of continuing interest.

 

• Physical and chemical characteristics of aluminums

Physical characteristics

Aluminium is a relatively sot, durable, light weight, ductile and malleable metal with appearance ranging from silvery to dull gray, depending on the surface roughness. It is non-magnetic and does not easily ignite. A fresh film of aluminium serves as a good reflection (approximately 92%) of visible light and an excellent reflector (as much as 98%) of medium and far infrared radiation. The yield strength of pure aluminium is 7-11Mpa while aluminium alloys have yield strength ranging form 200Mpa to 600Mpa [24] aluminiun has about one-third the density and shiftiness of steel. It is easily machined, cast, drawn and extruded. Aluminium atoms are arranged in a face-centered cubic (fcc) structure. Aluminum has stacking-fault energy of approximately 200mj/m2 [25]. Aluminium is a good thermal and electrical conductor, having 59% the conductivity of copper, both thermal and electrical, while having only 30% of copper’s density. Aluminium is capable of being a superconductor with a super conducting critical temperature of 1.2 Kelvin and a critical magnetic filed of about 100 gauss (10 milliteslias) [26].

Chemical characteristics

Corrosion resistance can be excellent due to a thin surface layer of aluminium oxide that forms when the metal is exposed to air, effectively preventing further oxidation, the strongest aluminium alloys are less corrosion resistance due to galvanic reactions with alloyed copper [24]. This corrosion resistance is also often greatly reduced by aqueous salts, particularly in the presence of dissimilar metals. Owing to its resistance to corrosion, aluminium is one of the few metals that retain silvery reflectance in finely powered form, making it an important component of silver0colored paint. Aluminium mirror finish has the hugest reflectance of any metal in the 200-400nm (uv) and the 3, 000-10000nm.

(Far IR) regions, in the 400-700nm visible range it is slightly out performed by tin and silver and in the 700-3000 (near IR) by silver, gold and copper [27].

Aluminium is oxidized by water to produce hydrogen and heat.

2Al + 3H₂0 – Al₂)₃ + 3H₂                                       (4)

This conversion is of interest for the production of hydrogen. Challenges include circumventing the formed oxide layer which inhibits the reaction and the express associated with the storage of energy by regeneration of all metal [28].

• 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].

• 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 (AlO_x (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.

• 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 1900-2000˚C. 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 2,000˚C (3, 600˚f). 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 950-980˚C (1, 740 to 1, 800˚f) 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].

• 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, 800˚C (3, 272˚f) 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, 291˚C (2, 356˚f). 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⁺

• 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.
  • 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.

• Etymology of aluminium

Two variants of the metals name are in current use, aluminium and aluminum (besides the obsolete aluminium) the International Union of Pure and Applied Chemistry (IUPAC) adopted aluminium as the standard international name for the element in 1990 but, three years later, recognized aluminium as an acceptable variant. Hence, their periodic table includes both. [53] IUPAC prefers the use of aluminium in these internal publications, although nearly as many IUPAC publications use the spelling aluminium. Most countries use the spelling aluminium, in the United State, the spelling aluminium predominates [54] the Canadian Oxford Dictionary prefers aluminium. In 1926, the American chemical society officially decided to use aluminium in its publication; American dictionaries typically label the spelling aluminium as a British variant. The name aluminium derives form old French, it ultimate sources, alumen, in turn is a Latin word that literacy means “Bitter salt” [55].  The earliest citation given in the Oxford English Dictionary for any word used as a name for this element is aluminium, which British chemist and inventor Humphry Davy employed in 1808 for the metal he was trying to isolate electrolytically from the mineral alumina. The citation is from the Journal philosophical transactions of the royal society of London: “has I been so fortunate as to have obtained more certain have certain evidences on this subject, and to have procured the metallic substance I was in search of, I should have proposed for them the names of silicon aluminium, Zirconium and glucium [56, 57].

• Aluminium alloys ins structural application

Aluminium alloys with a wide range of properties are used in engineering structures. Alloy systems are classified by a number system (ANSI) or by name indicating their main alloying constituents (DIN and ISO). The strength and durability of aluminium alloys very widely not only as a result of the components of the specific alloy, but also as a result of heat treatment and manufacturing processes. A lack of knowledge of these aspects has from time to time led to improperly designed structures and gained aluminium a bad reputation. One important structural limitation of aluminium alloys is their fatigue strengths. Unlike steels, aluminium alloys have no well-defined fatigue limit meaning that fatigue failure eventually occurs, under even very small cyclic loading. This implies that engineers must assess these loads ad design for a fixed life rather than an infinite life. Another important property of a aluminum also in their sensitivity heat. Workshop procedures involving heating are complicated by the fact that aluminium, unlike steel, melts without first glowing red forming operations where a blow torch is used therefore require some expertise, since all structural alloys, also are subject to internal stresses following heating operations such as welding and casting. The problem with melting point, which make the more susceptible to distortions from thermally induced stress reliefs controlled stress relief can be done during manufacturing by heat, treating the parts in an oven, followed by gradual cooling-in effect annealing the stresses.

• Alumina

Aluminium oxide aluminium oxide (Al₂O₃) and the associated oxy-hydroxides and trihydroxides are produced or extracted form minerals on a large scale. The great majority of this material is inverted to metallic aluminum about 10% of het production capacity is used for other applications. A major use is as an absorbent, for example alumina will remove eater from hydrocarbons, to enable subsequent processes that are poisoned by moisture. Aluminium oxides are common catalysts for industrial processes, e.g. the Claus process for converting hydrogen sulfide to sulfur in refines and for the alkylation of amines many industrial catalysts are “Supported” meaning generally that an expensive catalyst (e.g. platinum) is dispersed over a high surface area material such as alumina. Being a very hard materials (Mohs hardness), alumina is widely used as an abrasive and the production of applications that exploit its inertness, e.g. in high pressure sodium lamps.

• Effect of aluminium on plant

Aluminium is primary among the factors that reduce plant growth on acid soil. Although it is generally harmless to plant growth in PH neutral soils, the concentration in acid soils of toxic Al3+ cat ions increase and disturbs root growth and function [58, 59, 60, 61]. Most acid soils are saturated with aluminium rather than hydrogen ions. The acidity of the soil is therefore a result of hydrolysis of aluminium compounds. [62].This concept of “correct lime potential to define the degree of base saturation in soils became the basis for procedures now used in soil testing laboratories to determine the “line requirement” [63] of soils [64], wheat adaptation to allow aluminium tolerance is such that the aluminium induces a release of organic compounds that bind to the harmful aluminium cations sorghum is believed to have the same tolerance mechanism. The first gene for aluminium tolerance has been identified in wheat. It was shown that sorghum’s aluminium tolerance is controlled by a single gene, as for wheat [65] this is not the case in all plant.

• Importance of aluminum to health

Despite its natural abundance, aluminium has no known function in biology. It is remarkably non toxic, aluminium sulfate having an LD50 of 6207mg/kg (oral, mouse), which corresponds to 500 grams for 80kg person [23]. The extremely low acute toxicity notwithstanding, the health effects of aluminium are of interest in view of the widespread occurrence of the elements in the environmental and in commerce. Some toxicity can be traced to deposition in bone and the central nervous system, which is particularly increase in patients with reduced renal function. Because aluminum completes with calcium for absorption, increased amounts of dietary aluminium may contribute to reduce skeletal mineralization (osteopenia) observed in preterm infants and infants with growth retardation. In very high closes, aluminium can cause in euro toxicity and is associated with altered function of the blood-brain barrier [66] small percentage of people are allergic to aluminium and experience contact dermatitis, digestive disorders, vomiting or other symptoms upon contact or ingestion of products containing aluminium, such as deodorants or antacids. In those without allergies, aluminium is not as toxic as heavy metals, but there is evidence of some toxicity if it is consumed in excessive amount [67].

Although the use of aluminium cookware has not been shown to lead to aluminium toxicity in general, excessive use of aluminium containing antiperspirants provides more significant exposure level. Studies have shown that consumption of acidic food or liquid with aluminium significantly increase aluminium absorption, [68] and maltol has been shown to increase the accumulation of aluminium in nervous and osseus tissue. [69] Furthermore, aluminium increases estrogen-related gene expression inhuman breast cancer cells cultured in the laboratory [70]. The estrogen like effects of these slat have led to their classification as a metallostrogen. The effect of aluminium in antiperspirants has been examined over the course of decade with little evidence of skin irritation. [23] None the less, its occurrence in antiperspirants, dyes (such ads aluminium lake), and food additives is controversial in some quarters. Although here is little evidence that normal exposure to aluminium presents a risk to heath adults [71] some studies point to risks associated with increased exposure to the metal. [12] Aluminium in food may be absorbed more than aluminium form water. [73] Some researchers have expressed concerns that the aluminium in antiperspirant may increase the risk of breast cancer [74] ad aluminium has controversially been implicated as a factor in Alzheimer’s disease. [72]. The Camelford water pollution incident involved a number of people consuming aluminium sulfate. Investigations of the long-term health effects are still ongoing, but elevated brain in post-mortem examinations of victims, and further research to determine if there is a link with cerebral amyloidal antipathy has been commissioned [75].

• Solvent extraction

Solvent extraction is a method of separating by exploiting differences in the solubility’s of the component [76], solvent extraction can also be the partial removal of a substance from a solution or mixture by dissolving it in another immiscible solvent in which it is more soluble [77] for example, a coffee machine extracts the soluble components of ground coffee with water and leaves the insoluble components behind, the sample is shaken or mixed with solvent (or with two immiscible solvent) to affect the separation “the like dissolves like” is a useful guide for selecting solvents to use in extraction. Non polar substances are usually successfully extracted into non polar solvent like hexane or methylene chloride, polar and ionic substances are often extracted with water [76].

Solvent extraction can be said to be a method     of separating compound on the basis of their solubility in two different immiscible liquids like water and organic compound. We can also say that, it is a method of separating a compound which is soluble in an immiscible or a partially immiscible liquid which gives you a solute or in form of a residue. This forms different layers which facilities the separation of the compounds. The simplest solvent extraction example may be derived from water and an organic compound e.g. benzene is non-polar and is immiscible in was the polarity of water is very high. So it we want to separate benzene forma liquid which contains a component that dissolves in water, then we can mix it with water and the separation layer will be benzene [78]. Solvent extraction is commonly known for processing materials by using solvent to separate out various components within a materials sample. It is commonly used with liquids, but can also be employed for gasses and solids. [79]. In solvent extraction, a solvent is introduced to a material and as some components are more soluble than others, the sample starts to separate out, allowing people to remove the separated components individually [79].

1.7.1 Solvent extraction of metal

Solvent extraction is an important technology for the separation, purification and recovery of metals particularly uranium, copper, nickel, cobalt, and rare earths from solutions. Solvent extraction uses an organic containing a special reagent (extraction) to transport selected metals from one aqueous solution to another, so that metals are separated, purified and recovered for example, after mixing an organic solution with an aqueous solution containing copper, iron and other impurities (feed), the organic solution selectivity extracts copper and leaves iron and other impurity in the aqueous solution (raffinate). This step is called extraction. In the next step, termed stripping, the copper in the organic solution is tripped by an acidic solution (spent electrolyte) to form a loaded strip liquor (loaded electrolyte) resulting in a much purer copper solution. If the volume of the strip solution is much smaller than that of the organic solution, copper is concentrated. In the next step, which may be electro wining, the copper in the loaded strip liquor is deposited onto a cathode and pure copper is obtained. Factors such as the composition of feed solution and the nature of metal to be purified must be considered when selecting solvent extraction technology [80].

The extraction methods for a range of metals include [81]:

• Cobalt: The extraction of cobalt from hydrochloric acid using alamine 336 in metaxylene [82], cobalt can be extracted also using cyanex 272 (bis-(2, 4, 4-trimethylepentyl) phosphinic acid).
• Copper: Copper can extracted using hydroxyoxines as extracants, a recent paper describes an extratant that has a good selectively for copper over cobalt ad nickel [83].
• Neodymium: This rate earth is extracted by di(2-ethylhexyl) phosphorus acid into hexane by ion exchange mechanism [84].
• Nickel: Nickel can be extracted using di (2-ethyl-hexyl) phosphoric acid and tributyl phosphate in hydrocarbon diluents (Shellsol). [85].
• Palladium and platinum: Dialkyl sulfides, tributyl phosphoric acid and tributyl phosphate and alkyl amines have been used for extracting these metals [86, 87].
• Zinc and cadmium: The Zinc and cadmium are both extracted by and ion exchange process [88].

In modified Zincex process, Zinc is separated from most divalent ions by solvent extraction. D2EHPA (Di (2) ethyl hexyl phosphoric acid) is used for this extraction; a Zinc ion replaces the proton form two D2EPHPA molecules. To strip the Zinc form the D2EHPA, sulfuric acid is used, at a concentration of above 17g/h (typically 240-265g/l) [86].

In mineral processing, the composition of the feed solution is complicated and the valuable metal to be purified varies [80].