Dissolution Kinetic And Solvent Extraction Of Aluminium From Kaolin

1.1.2 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 550-600Ëšc to produce disordered metkaolin, Al2Si207, but continuously hydroxyl loss (-OH) s observed up to 900Ëšc 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, 3Al2 O3.2SiO2, and highly crystalline cristobalite, SiO2

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

1.2 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].  

1.3 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.

 1.3.1 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].