THE PROCESS of ALUMINUM PRODUCT

What is Aluminum?

Aluminium is a soft, durable, lightweight, malleable metal with appearance ranging from silvery to dull grey,

depending on the surface roughness. Aluminium is nonmagnetic and nonsparking. It is also insoluble in

alcohol, though it can be soluble in water in certain forms.

Aluminium has about one-third the density and stiffness of steel. It is ductile, and easily machined, cast, drawn and

extruded.

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 aluminum alloys are less corrosion resistant due to galvanic reactions

with alloyed copper. This corrosion resistance is also often greatly reduced when

many aqueous salts are present however, particularly in the presence of dissimilar metals.

Aluminium is a good thermal and electrical conductor, by weight better than copper.

Aluminium is capable of being a superconductor, with a superconducting critical

temperature of 1.2 kelvin and a critical magnetic field of about 100 gauss.[8]

Aluminium is a strongly reactive metal that forms a high-energy chemical bond with oxygen. Compared to most other metals, it is difficult to extract from ore, such as bauxite, due to the energy required to reduce aluminium

oxide (Al2O3). For example, direct reduction with carbon, as is used to produce iron, is not chemically possible, since aluminium is a stronger

reducing agent than carbon. However there is an indirect carbothermic reduction possible by using carbon and Al2O3 which forms an intermediate Al4C3 and this can further yield aluminum metal at a temperature of 1900-

2000°C. This process is still under development. This process costs less energy and yields less CO2 than the Hall-Héroult process. Aluminium oxide has a

melting point of about 2,000 °C. Therefore, it must be extracted by electrolysis. In this process, the aluminium oxide is dissolved in molten

cryolite and then reduced to the pure metal. The operational temperature of the reduction cells is around 950 to 980 °C. Cryolite is found as a mineral in

Greenland, but in industrial use it has been replaced by a synthetic substance. Cryolite is a chemical compound of aluminium, sodium, and calcium fluorides:

(Na3AlF6)

How process of AluminumProduct ?

STAGE 1

Converting Bauxite to Alumina

STEP 1-Crushing and Grinding

Step1-Crushing and GrindingStep1-Crushing and GrindingStep1-Crushing and Grinding

STEP 2-Digesting STEP 3- Settling

STEP 4- PrecipitationSTEP 5-Calcination

Process of Aluminum Product

STAGE 1Converting bauxite to Alumunia

STEP 1- Crushing and Grinding: Alumina recovery begins by passing the bauxite through screens to sort it by size. It is then crushed to produce relatively uniformly sized material. The ore is then fed into large grinding mills and mixed with a caustic soda solution (sodium hydroxide) at high temperature and pressure. The grinding mill rotates like a huge drum while steel rods - rolling around loose inside the mill - grind the ore to an even finer consistency. The process is a lot like a kitchen blender only much slower and much larger. The material finally discharged from the mill is called slurry.

Bauksite

STAGE 2Converting Alumina to Aluminum

Smelting Aluminum is formed at about 900 °C, but once formed has a melting point of only 660 °C. In some smelters this spare heat is used to melt recycled metal, which is then blended with the new metal. Recycled metal requires only 5 per cent of the energy required to make new

metal.

Potlines

STEP 2-Digesting: The slurry is pumped to a digester where the chemical reaction to dissolve the alumina takes place. In the digester the slurry - under 50 pounds per square inch pressure - is heated to 300 °Fahrenheit (145 °Celsius). It remains in the

digester under those conditions from 30 minutes to several hours. More caustic soda is added to dissolve aluminum containing compounds in the slurry. Undesirable compounds either don't dissolve in the caustic soda, or combine with other compounds to create a scale on equipment which must be periodically cleaned. The digestion process produces a sodium aluminate solution. Because all of this takes place in a pressure cooker, the slurry is

pumped into a series of "flash tanks" to reduce the pressure and heat before it is transferred into "settling tanks."

Alumina

STEP 3-Settling: Settling is achieved primarily by using gravity, although some

chemicals are added to aid the process. Just as a glass of sugar water with fine sand

suspended in it will separate out over time, the impurities in the slurry - things like

sand and iron and other trace elements that do not dissolve - will eventually settle to

the bottom.

STEP 4-Precipitation: Precipitation is a process filtering to get alumina. Imagine a tank as tall as a six-story building. Now imagine row

after row of those tanks called precipitators. The clear sodium aluminate from the settling and

filtering operation is pumped into these precipitators. Fine particles of alumina - called alumina

hydrate are added to start the precipitation of pure alumina particles as the liquor cools.

STEP 5-Calcination: Calcination is a heating process to remove the chemically

combined water from the alumina hydrate. That's why, once the hydrated alumina is

calcined, it is referred to as anhydrous alumina. "Anhydrous" means "without water."

STAGE 2Converting Alumunia to Aluminum

Smelting: The Hall-Heroult process takes place in a large carbon or

graphitelined steel container called a " reduction pot". In most plants, the

pots are lined up in long rows, called potlines. The key to the chemical

reaction necessary to convert talumina to metallic aluminum is the running of

an electrical current through the cryolite/alumina

mixture. The process requires the use of direct current (DC).