For manufacturers, no matter what industry you’re in, understanding the various processes involved in working with materials such as aluminum is an essential part of your job. It’s important to know the essential properties of various grades and alloys of the metals you are working with, and comprehend how different materials will respond to different techniques and applications. One of the most important methods of working with aluminum is smelting, and that’s what we will be discussing today.
As you read about the aluminum smelting process, don’t forget that the trained technical professionals at Clinton Aluminum are standing by to help customers like you find just the right material for every job. Contact us today to learn more.
Why Is Aluminum So common Yet So Rare?
Smelting is a crucial step in aluminum extraction, and without it, it would be extremely difficult to access aluminum in the first place, let alone use it as a building or commercial material. This is because while aluminum is the third most abundant element following oxygen and silicon in the Earth’s crust, it is actually rarely found naturally in its native form. Pure aluminum is highly reactive and its molecules quickly and easily bond to nearby elements.
The reason for aluminum’s prevalence on Earth (the metal accounts for approximately 1.59% of the planet’s mass) is because it so easily forms as an oxide and is bound into rocks and therefore is not easily shed into the atmosphere. While rarely encountered in pure form, it often forms into oxides and silicates. Common aluminum-containing minerals include beryl, cryolite, garnet, spinel, and turquoise. Rubies and sapphires are formed from impurities in aluminum oxide.
Of all the various minerals that contain aluminum, the one that is most responsible for its commercial viability is bauxite. Most commonly found in tropical climates, bauxite is currently mined in abundance in places such as Australia, China, Guinea, and India. The process by which the aluminum is extracted from bauxite is known as smelting.
What Is The Bayer Process?
The process of converting bauxite to pure aluminum typically involves two distinct steps. First, the mineral will be subjected to the Bayer process, which is used to extract alumina (another name for aluminum oxide) from the bauxite. The alumina is then put through the Hall-Héroult process, which involves dissolving the alumina in molten cryolite and electrolyzing the molten salt bath.
The Bayer process was developed by Carl Josef Bayer in 1888 while working in the textile industry to develop a cheap method for extracting alumina, which was commonly used for dyeing cotton. The main composition of bauxite ore is hydrated aluminum oxides mixed with the compounds of elements such as iron. Bayer discovered that it was possible to heat the ore in a pressure vessel while adding in a sodium hydroxide solution known as caustic soda at a temperature between 150 and 200 degrees Celsius. The aluminum dissolves as sodium aluminate during the extraction process.
It is important to note that the aluminum in bauxite can be one of several compounds, such as gibbsite (Al(OH)3), boehmite (AlO(OH)), or diaspore (a-AlO(OH)). Each compound will require a different method of extraction, though the general process will be the same. Different forms of the aluminum component dictate the particular extraction conditions. Following the separation of the residue, gibbsite will be precipitated when the liquid is cooled, seeding it with fine-grained aluminum hydroxide.
During the extraction, the aluminum oxide found in the bauxite is converted into the soluble sodium aluminate. Silica is also dissolved, while the other compounds contained in the bauxite remain solid. The impurities can then be filtered out using a rotary sand trap or other methods. The waste product of the process is referred to as red mud and is made up of high calcium and sodium hydroxide content.
What Is The Hall-Héroult Process?
Once the alumina has been extracted from the bauxite ore, it can then be subjected to the Hall-Héroult process, which is an electrolytic process that was developed independently at the same time by Charles Martin Hall and Paul Héroult in 1886. Until that time, there was no commercially viable way to extract aluminum, due to the fact that it’s not possible to produce aluminum via the electrolysis of an aqueous aluminum salt. The problem is that hydronium ions easily oxidize elemental aluminum. And while it is possible to do so with molten aluminum salt, aluminum oxide has a melting point of 2072 degrees Celsius, making it impractical.
The Hall–Héroult process takes alumina and dissolves it in molten synthetic cryolite. This avoids the above problem by lowering the melting point to make electrolysis more possible. The melting point of cryolite, once some alumina has been added to it, is around 1000 degrees Celsius, less than half that of aluminum salt. Other benefits of using cryolite include the fact that it makes it easy to dissolve the alumina, it conducts electricity, and has a lower density than aluminum.
During the electrolysis, the liquid aluminum is deposited at the cathode. At the same time, the oxygen from the alumina combines with carbon to produce carbon dioxide.
A typical aluminum smelter requires a great deal of electricity to function properly. This means that smelters are often built near to or in conjunction with large power stations. They also are situated near ports, because typically the alumina will need to be imported from overseas.
Understanding how aluminum is sourced helps manufacturers to have a better grasp on where the metal comes from and how it gets turned into the many diverse alloys that make it so valuable for commercial applications. No matter what your aluminum needs, the professional and experienced team at Clinton Aluminum is able to help. Our goal is to be more than just a material provider but to become true partners to our clients.
We pride ourselves in being able to assist you at every step of the production process, from the initial planning to the final execution. Contact us today to learn more about how Clinton Aluminum can help you save money while producing a more competitive product.