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HALL HEROULT PROCESS PDF

Hall-Heroult Process. • Electrochemical Process to Reduce Alumina to Aluminum . – Alumina is dissolved in a molten fluoride solvent called cryolite. 2 Al. 2. O. Aluminium is produced according with the Hall-Heroult process. During this complex electrolyte two-phase electrolysis, it is difficult to model the current. Hall-Héroult process: metallurgy: Electrolytic smelting: In the Hall-Héroult smelting process, a nearly pure aluminum oxide compound called alumina is dissolved.

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Chemical processes Aluminium industry Electrolysis. The density of liquid aluminum is 2. The density of the electrolyte should be less than 2. In addition to AlF 3other additives like lithium fluoride may be added to alter different properties melting point, density, conductivity etc. The aluminium sinks to the bottom of the electrolytic cell, where it is periodically collected.

Aluminium is the most abundant metallic element in the Earth’s crust, but it is rarely found in its elemental state. Electrodes in cells are mostly coke which has been purified at high temperatures.

Hall–Héroult process

Alumina is added to the electrolyte from between the ball in prebake technology using cells. The cell produces gases at the anode. The materials most often used in anodes, coke and pitch resin, are mainly residues from petroleum industry and need to be of high enough purity so no impurities end up into the molten aluminum or the electrolyte. The remains of prebaked anodes are heroulh to make more new prebaked anodes.

In other projects Wikimedia Commons. Anode effect decreases the energy-efficiency and the aluminium production of the cell.

Hall–Héroult process – Wikipedia

This meant the cost to produce the small amount of aluminium made in the early 19th century was very high, higher than for gold or platinum. The following is a schematic picture of an aluminum electrolysis cell: Temperature within the cell is maintained via electrical resistance. More material to the top of the anode is continuously added in the form of briquettes made from coke and pitch. Prebake technology is named after its anodes, which are baked in very large gas-fired ovens at high temperature before being lowered by various heavy industrial lifting systems into the electrolytic solution.

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Carbon anodes are immersed into the electrolyte usually referred as the “bath” carrying electrical current which then flows into the molten cryolite containing dissolved alumina.

National Historic Chemical Landmarks. The anode is in a frame and as the bottom of the anode turns mainly into CO 2 during the electrolysis the anode loses mass and being amorphous it slowly sinks within its frame.

From Wikipedia, the free encyclopedia. Prebaked anodes either are made in the same factory where electrolysis happens or are brought there from elsewhere. Cells in factories are operated 24 hours a day so that the molten material in them will not solidify.

The aluminum is produced extracting it from the aluminum oxide Al 2 O 3called also alumina, through an electrolysis process driven by electrical current. It occurs in many minerals but its jeroult commercial source is bauxitea mixture of hydrated aluminium oxides and compounds of other elements such as iron.

Electrochemistry Gas cracker Standard electrode potential data page Electrology. The lost heat from the smelting operation is used to bake the briquettes into the carbon form required for reaction with alumina. In modern facilities fluorides are almost completely recycled to the cells and therefore used again in the electrolysis.

It later became heroulg Alcoa corporation. Cathodes also degrade during electrolysis, but much more slowly than anodes do, and thus they need neither be as high in purity nor be maintained as often. Besides having a relatively low melting point, cryolite is used as an electrolyte because among other things it also dissolves alumina well, conducts electricity, dissociates electrolytically at higher voltage than alumina and has a lighter density than aluminum at the temperatures required by the electrolysis.

Escaped HF can be neutralized to its sodium salt, sodium fluoride. This page was last edited on 13 Decemberat Oxidation of the carbon anode increases the electrical efficiency at a cost of consuming the procesx electrodes and producing carbon dioxide.

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Recycled aluminum requires no electrolysis, thus it does not end up in this process. It also induces the formation of tetrafluoromethane CF 4 in significant quantities, increased formation of CO and to lesser extent also causes the formation of hexafluoroethane C 2 F 6.

The Hall-Héroult Process Basics – The Aluminum Smelting Process

The liquid aluminium is removed from the cell via a siphon every 1 to 3 days in order to avoid having to use extremely high temperature valves and pumps. The method was complicated and consumed materials that were in themselves expensive at that time.

This requires the whole cell to be shut down. This heats up the gas layer and causes it to expand thus further reducing the surface area where electrolyte and anode are in contact with each other.

Agitation of the molten material in the cell increases its production rate at the expense of an increase in cryolite impurities in the product. By using this site, you agree to the Terms of Use and Privacy Policy. The following is a schematic picture of an aluminum electrolysis cell:. Views Read Edit View history.

The exhaust is ;rocess CO 2 produced from the anode consumption and hydrogen fluoride HF from the cryolite and flux AlF 3. Retrieved 19 April This causes liquid aluminium metal to be deposited at the cathode while the oxygen from the alumina combines with carbon from the anode to produce mostly carbon dioxide. Once passed through the bath, the electrical current flows into the molten aluminum deposit and is then collected by the bottom of the pot, usually called “cathode”.