What is the difference between alumina and bauxite

In the U. Brazil, India and Jamaica also have some significant reserves of the metal. Bauxite is a more general term for a piece of rock made of oxides of hydrated aluminum. It is the primary ore of alumina, which is used to make the actual aluminum. This ore is also utilized in making aluminous refractories and synthetic corundum. Bauxite is actually reddish brown in color and can also appear white, tan yellow or simply tan.

Color wise, aluminum appears to be a silvery white metal that is very light weight. It is actually three times as dense as ordinary water but its toughness is without question. This is the reason why many transportation vehicles including the most advanced like space shuttles and airplanes make use of plenty of aluminum to coat the vehicle thus making it sturdy; and at the same time as light as possible for ease of travel. Aluminum also has many uses at home making it a very popular element to most common people.

In this connection, aluminum is a very ductile element. This property enables aluminum to be firmly pressed into fine thin sheets aluminum foils and even drawn into wires. Aluminum is a very reactive type of metal.

Because of this, it is not able to exist naturally in nature. It easily reacts to both air and water forming some hydroxides and powdery oxides.

Gangue solids, usually iron oxides, quartz, and other resistant minerals, are separated from the hot sodium aluminate slurry by physical means such as settling and filtration. The solids red mud and red sand are countercurrent washed to recover the caustic solutions, then pumped to specially designed impoundment beds. The mud and sand can be intercepted, neutralized, washed, and stored for reuse [ 2 ]. The chemical reactions leading to the alumina as final product are given above.

Growing awareness has led to a multitude of studies and semi-industrial trials related to the recycle or valorization of RM as a raw material for different industrial applications. An application in building materials, as a component in OPC, filler material, or geopolymers, seems to be a straightforward approach in terms of high quantity reuses [ 1 ].

Generally, the use of geopolymer as an alternative binder drew the attention because of its excellent properties, such as high compressive strength, resistance to acidic solutions, and thermal stability, in combination with their lower CO 2 footprint [ 7 ]. The quantity of alumina produced from bauxite ore depends on the type and the composition of the bauxite ore. Generally authors agree that 1 ton of alumina is produced from 3 ton of bauxite [ 9 ].

In average the RM generated per ton of alumina varies between 1 and 1. The quantity of bauxite residue generated at a particular refinery is governed by the processing conditions and bauxite quality [ 10 ]. The global inventory of RM stored on land currently is estimated to be over 2.

Figure 2 is a schema allowing the assessment of the accurate amount of alumina and the resulting RM obtainable from crude bauxite. Calculation scheme for the amount of alumina and red mud that turn out during alumina refinery using chemical and mineralogical data [ 12 ]. Bauxite mining and processing have a strong and varied impact on the environment because they entail modifications of the landscape and severe pollution by rejecting wastes into the biosphere soil, the atmosphere and the water [ 13 ].

Among others RM causes: i contamination of water resources with caustic soda and metallic oxide-bearing impurities; ii direct contact with fauna and flora; iii evaporation that could originate highly alkaline rainfalls; iv visual impact on extensive areas [ 14 ]. The variation in chemical composition between red mud worldwide is high. The major chemical composition of red mud for selected countries over the world is presented in Table 2.

As and etc. The variation in chemical composition between red mud worldwide is high [ 9 ]. The major chemical composition of red mud for selected countries over the world is presented in Table 3. Bauxite potential of Guinea billions of tones [ 6 , 7 ]. Chemical composition of red mud generated in alumina plants in various countries adapted from [ 13 ]. ACG plant rejects 1 ton of mud per ton of alumina produced and that each ton of mud contains on average 15 kilograms of caustic soda NaOH which has not been recovered by washing [ 11 ].

The increasing need of the industry sectors involving aluminum as metal, entailed the improvement of the Bayer process and the subsequent issue of the management of RM. Despite several years of research on the possible valorization of this waste, there is almost no evidence of a large-scale application of this industrial waste to date.

Globally research efforts are focused on three fields for the valorization or reuse of RM: Civil and chemical engineering applications. This chapter addresses specifically the use of RM for the production of geopolymers for construction and other engineering applications.

A polymer is a macromolecule, organic or inorganic, consisting of the repeated sequence of the same pattern, the monomer from Greek monos: one or only one, and meros: part , connected to each other by covalent bonds.

The constituent unit is A; it is formed of a group of atoms that repeats itself. Geopolymer is a class of inorganic polymers generally formed by the chemical reaction between silica-rich and alumina-rich solids with a high alkaline solution. It is assumed that they result from the dissolution of alumina and silica into a silicate solution occurring the polycondensation of these monomers into aluminosilicate anions.

In the chapter below the role of Al 2 O 3 as precursor or monomers provider in geopolymerization will be highlighted. The GP technology has recently attracted increasing attention as a viable solution to reuse and recycle industrial solid wastes and by-products. It provides a sustainable and cost-effective development for many issues where hazardous residues have to be treated and stored under critical environmental conditions [ 15 ].

Generally, materials containing mostly amorphous silica SiO 2 and alumina Al 2 O 3 are a possible source for GP production. Furthermore Geopolymers appear to be a potential alternative to the classic hydraulic binders.

Some research studies have been carried on to produce alkali-activated materials from RM. The authors obtained Bragg used a method based on the theory of distinct silicate or aluminate anions as the basic unit of constitution. This central unit is a tetrahedral complex consisting of a small cation such as Si or Al that lies in tetrahedral coordination with 4 oxygen anions to produce SiO 4 or AlO 4.

The silicon-oxygen bond should never be ionic; it should be polar and covalent [ 5 ]. This is since specific silicon and oxygen atoms Cannot move at liberty within the crystalline structure. Aluminosilicate based geopolymers such as polysialate consist of SiO 4 and AlO 4 tetrahedra which are linked alternatively by sharing all the oxygen atoms [ 5 ].

Alkali-activated binders have either amorphous or nanocrystalline microstructures. This depends on the amount of alumino-silicate content in the precursor materials and on the mineralogical nature mineralogy of raw materials [ 17 ]. Classification of Geopolymers [ 17 ]. Further GP are broadly classified as acid activated and alkali activated geopolymers as shown in Figure 1. Acid activated geopolymers were recently introduced, having properties comparable to alkali activated materials e.

The higher porosity of this group of polymers suggested their possible application in waste water treatment and as an adsorbent [ 20 ]. Acid activated geopolymers have not been explored and further research in this field is required. Alkali activated GP are materials of special interest in the past four decades due to their superior properties compared to OPC.

Based on the alumino silicate matrix they are classified as sialate, sialate silaxo and sialate di silaxo. Starting materials are checked for pozzolanic content i. With the advanced mixing technologies, mix design comprised of pozzolanic and semi pozzolanic waste materials have been reported.

The base materials found to be suitable comprise natural minerals such as metakaolin, clays, which contains Si, Al and oxygen in their chemical composition [ 16 ]. Disposal, price, application and demand of the users are the main factors in the process of the selection of source materials [ 4 ]. In order to obtain a GP with desired properties e. It is therefore of major importance to characterize the aluminosilicate source and to determine their reactivity, in order to be able to evaluate the amount silicates and aluminates reacting.

It should be noted that the particles size distribution or fineness is of importance regarding the reactivity of the aluminosilicate source. The mix can then be optimized by adjusting the type and the amount activators added. Most of the investigations have used alkali solutions for dissolution of raw materials to form the reactive precursors necessary for geopolymerization. It has been shown that silicate activation increases the dissolution of the starting materials and gives rise to favorable mechanical properties [ 21 ].

Two groups of materials are required to make a geopolymer; one is source materials containing alumina and silica and other is an alkali that activates the polymerization reaction. Basing on their origin materials of the first group are natural or industrial mainly by-products.

Kaolinite microsilica : is a clay mineral having the chemical composition Al 2 Si 2 O 5 OH 4 Rocks that are rich in kaolinite are known as kaolin or china clay. Kaolinite is a clay mineral with the chemical composition Al 2 S 2 O 5 OH 4 , which means each particle has one tetrahedral silica layer and one octahedral alumina layer [ 15 ].

It is a soft, earthy, usually white mineral, produced by the chemical weathering of aluminum silicate minerals like feldspar.

Rocks that are rich in kaolinite are known as china clay, white clay, or kaolin. Kaolin is a fine, white, clay mineral that has been traditionally used in the manufacture of porcelain. It is a highly pozzolanic and reactive material. Kaolinite is a clay mineral with the chemical composition Al 2 Si 2 O 5 OH 4 , which means each particle has one tetrahedral silica layer and one octahedral alumina layer.

Fly ash: fly ash is defined as the finely divided residue that results from the combustion of ground or powdered coal and that is transported by flue gasses from the combustion zone to the particle removal system. The characteristics of fly ash are loss on ignition LOI , fineness and uniformity. LOI is a measurement of unburnt carbon remaining in the ash.

Finer gradation generally results in a more reactive ash and contains less carbon. Fly ash is a very fine, powdery material, composed mostly of silica. It consists mostly of silt-sized and clay-sized glassy spheres. These are generally spherical in shape and range in size from 0. They consist mostly of SiO 2 , which is present in two forms: amorphous, which is rounded and smooth, and crystalline, which is sharp, pointed and hazardous.

The chief difference between these classes is the amount of calcium, silica, alumina, and iron content in the ash. Rice-husk ash : Rice husk is the natural sheath that forms on rice grain during its growth. Removed during the refining of rice, the rice husk ash RHA is generated after burning the rice husk in the boiler. At present, the most common method of disposal of RHA is dumping on waste land, thus creating an environmental hazard through pollution and land dereliction problems.

The major compounds from rice husk are silica and cellulose which yields carbon when thermally decomposed [ 22 ]. At higher temperatures the RHA color tends to white and its Si content increases. This is stronger, less permeable and more resistant to chemical attack. Due to its insulating properties, RHA has been used in the manufacture of refractory bricks. Recently RHA has been incorporated in activated aluminosilicates.

Catalyst residues: Petroleum refineries worldwide process crude oil in fluid catalytic cracking FCC units, and , tons of spent FCC catalyst residue are thus produced every year [ 23 ]. The spent catalyst is essentially an agglomeration of zeolite faujasite crystals held together by an aluminosilicate matrix including amorphous silica and clays. Catalysts from different sources and processes also differ in composition and reactivity, meaning that this is rather a diverse class of materials which can provide alkali-activated products with a range of performance levels [ 24 ].

Request new password. Search form Search. The Aluminum Advantage. Aluminum Advantage. Product Markets. Members Area. Home » Industries » Production » Alumina Refining. Buyer's Guide. Alumina Refining. Quick Read Alumina is the common name given to aluminum oxide Al 2 O 3.

Take-Away Facts The Bayer process is used to produce alumina The Bayer process, invented in , is the primary process by which alumina is extracted from bauxite ore. Alumina has many industrial uses Alumina is used for key industrial purposes other than producing aluminum.

The production of spark plug insulators and metallic paint, and its use as a fuel component for solid rocket boosters are but a few examples. Cutting-edge technology applications Alumina is used as a tunnel barrier for fabrication of superconducting devices such as quantum interference devices and electron transistors.

The oxide is also used as a dosimeter for radiation protection. Alumina Description of alumina aluminum oxide Alumina is properly called aluminum oxide, which is a chemical compound comprised of aluminum and oxygen molecules Al 2 O 3. The Bayer process: How alumina is produced from bauxite The Bayer process is carried out in four steps.

Industrial uses of alumina In addition to its use in the production of primary aluminum, aluminum oxide has other key industrial uses.