It's a rare natural fluoride mineral which due to its scarcity in natural form has been manufactured artificially. In modern metal production, cryolite is made by mixing hydrofluoric acid with aluminium hydroxide and soda. Aluminium Production. So we've mined bauxite, made alumina from it and stockpiled cryolite, and now everything is ready for the last stage: electrolytic reduction to make aluminium. The reduction area is the heart of an aluminium smelter and it looks very different from the production shops in your typical steel works that make cast iron or steel.
The reduction area consists of several rectangular buildings whose length sometimes exceeds 1 kilometre. Inside there are hundreds of reduction cells or pots arranged in rows and hooked up to power sources via massive cables. The constant voltage at the electrodes of each reduction cell varies in the range of between 4 and 6 volts, while the amperage can reach , KA and more.
It's the electric current that is the main production force in this process. There are only a handful of people in a typical reduction area as all the key processes are automated. Current for aluminium production To start a car engine, current of A is needed for 30 seconds. That's times less than one reduction cell requires on an ongoing basis.
In each reduction cell, aluminium is produced from alumina via the electrolytic reduction process. The entire cell is filled up with molten cryolite that creates a conductive environment at a temperature of oC.
The bottom of the cell works as the cathode while the role of the cathode is played by special cryolite-carbon blocks 1.
These blocks look like massive hammers. Every thirty minutes an automatic alumina feeding system dumps a new portion of alumina into the cell. The electric current flowing through the cell breaks down the bond between aluminium and oxygen, causing aluminium to settle to the bottom of the cell and form a layer cm deep while the oxygen binds with the carbon in the anode blocks to form carbon dioxide. Two to four times per day, aluminium gets extracted from the cell with special vacuum buckets.
A hole is punched in the cryolite crust that forms on the surface of the reduction cell, then a pipe is lowered in through the hole. Through this pipe liquid aluminium is sucked into the bucket, from which all air is pumped out in advance. On average, about 1 tonne of metal is recovered from every reduction cell while a vacuum bucket can hold 4 tonnes of molten aluminium. Once the bucket is full it is taken to the casthouse. For every tonne of aluminium produced, , cubic metres of gases are emitted.
For this reason, every reduction cell, regardless of its design, is equipped with a gas removal system that catches the gases emitted during the reduction process and directs them into a gas treatment plant. Modern dry gas treatment systems use alumina to filter out toxic fluoride compounds from the gases. So before being used in aluminium production, alumina is first used to treat the gases emitted during the earlier production of aluminium. So it's a closed loop, in a sense.
The aluminium reduction process requires huge amounts of electric power, so it's important to use renewable energy sources that don't contaminate the environment. The most common renewable energy source is a hydroelectric power plant, as they can deliver the required power without contaminating the atmosphere.
When hydroelectric power is used just 4 tonnes of carbon dioxide is emitted into the atmosphere per each tonne of aluminium produced, but when coal-fired generation is used, five times as much carbon dioxide is emitted per each tonne of output, or Carbon dioxide.
In one sunny day one hectare of forest consumes kg of carbon dioxide from the atmosphere and emits kg of oxygen. Molten aluminium istransported in buckets to the casthouse of the smelter. At this stage the metal still contains a lot of iron, silicon, copper and other elements. However, even the smallest amounts of admixtures can have a drastic impact on the properties of aluminium, so in the casthouse all admixtures are removed by remelting the aluminium in a special furnace at o C.
The resultant pure aluminium is cast into special moulds where it is allowed to solidify. The smallest aluminium ingots, often called pigs, weigh between 6 and When customers get aluminium delivered to them in pigs they remelt them, add whatever components they need and then recast them in the shape needed for their purposes.
The largest ingots, tonne slabs Hot aluminium is poured into a mould like this over a period of two hours, with the slab 'growing' in the mould like an icicle, only from the bottom up. As the slab is cast, it is cooled down with water and as soon as the casting process is complete, the slab is ready for shipment.
Slabs are usually then rolled into thin sheets that are then used in the manufacture of foil, beverage cans or automobile body panels. Extrusion is the process used for making the vast majority of aluminium products. In the casthouse, not only is aluminium given the required shape but also the required chemical composition. The thing is that pure aluminium is used far less than aluminium alloys. During this process, the aluminum becomes solid.
This results in large aluminum crystals which are filtered and washed to remove water and other impurities. Now the aluminum hydroxide crystals are subjected to calcination, a thermal treatment process where the supply of air is controlled.
Smelting is the process during which aluminum is extracted from the alumina. The smelting takes place in steel reduction pots filled with molten electrolyte, where carbon anodes are used to pass an electric current through the electrolyte. Alumina is then added to the molten surface. The electric current deposits molten aluminum which can be collected and siphoned off.
The molten aluminum is then poured into molds to form foundry ingot. Now it can be further refined to produce superpure aluminum or used for alloying with other metals. Superpure aluminum of high purity However, it is corrosion-resistant and an excellent conductor of electricity.
Superpure aluminum is used in chemical equipment, electronic components, and to make gasoline. Most aluminum is alloyed with other elements. By alloying the aluminum, its hardness and strength can be significantly improved. Common aluminum alloys are aluminum-manganese used in beverage containers , aluminum-magnesium used in appliances and utensils , aluminum-magnesium-silicon used in buildings and vehicles , and aluminum-copper used in aircraft.
Aluminum can be endlessly recycled without losing its quality. This makes it one of the most environmentally friendly metals on the planet. Incredibly, most of the aluminum ever produced is still being used today. We are metal experts and have been providing quality customer service and products since Show details about this statistic. Exclusive Premium functionality. Register in seconds and access exclusive features.
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