explain bayers process with example......
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Alumina:
Alumina also known as Aluminium Oxide is an amphoteric oxide comprising of aluminium and oxygen. Alumina is symbolised as Al2O3. Alumina has the appearance of white solid like table salt.
Alumina has a boiling point of 2980 degree Celsius and melting point of 2040 degree Celsius. Its molar mass is 101.96 g/mol.
The Bayer Process:
Alumina is the main components of bauxite, so bauxite is refined in order to produce Alumina. The Bayer process is the principal way for producing alumina by refining Bauxite. Bauxite other than with 30-60percentage of aluminium oxide contains mixture of silica, iron oxides and titanium dioxide.
Bayer process of producing alumina can be divided into following four steps:
i. Digestion:
In this step of Bayer process, bauxite ore is crushed, milled and then heated with sodium hydroxide at the temperature of around 150-200 degree Celsius. In the Bauxites, aluminium compounds are present as gibbsite (Al (OH) 3), boehmite (AlOOH) and diaspore (α-AlO (OH)).
ii. Filtration:
In this step the mixture is clarified to remove impurities. Other than alumina and silica, all other components present in Bauxite do not get dissolved. The solids which are not dissolved get settled down at the bottom forming red mud. This red mud is then discarded from the solution commonly by using rotary sand trap.
The filtration process converts the aluminium oxide to soluble sodium aluminates, 2NaAlO2, as per the equation:
Al2O3 + 2NaOH → 2NaAlO2 + H2O.
iii. Precipitation:
The clear remaining mixture is added to precipitators by using heat exchangers, which turns the mixture from heat to cool liquor. Silica is precipitated from the mixture because heating. Crystals of aluminium hydroxide are discovered in this step. Some amount of aluminium hydroxide discovered in this step is used as a water treatment chemical.
iv. Calcination:
90 percentage of the gibbsite manufactured is converted into alumina by washing, drying, and then heating aluminium hydroxide in a rotary klins or fluid flash calciners at temperature 1010-1260 degree Celsius.
2 Al (OH) 3 → Al2O3 + 3 H2O.
More than 90 percent of alumina manufactured is used to produce aluminium by Hall-Heroult Process.
History of the Bayer Process:
Bayer process was invented by Austrian chemist, Carl Josef Bayer in 1887, while working in Saint Petersburg, Russia for developing a method to supply alumina to the textile industry.
The Bayer process started gaining importance after the invention of Hall-Heroult aluminium process. Till today the process is unchanged and is used to produce nearly all the world’s alumina supply.
Applications of Alumina:
Along with use of chemical alumina in the production of aluminium it has other key uses.
Being chemically inert and white in appearance, aluminium is preferred as filler in plastics.
In sunscreen it is a common ingredient and is sometimes also present in cosmetics like lipsticks, blush and nail paints.
In many glass formulations, alumina is used as an ingredient.
Alumina is used in purification, to remove water from gas streams.
In Claus process alumina is the catalyst. It is also used for dehydrating alcohols to alkenes.
Aluminium oxide is widely uses as an abrasive because of its strength and hardness.
Paint: Flakes of alumina are used for reflective decorations in paints, like in automotive or cosmetics industry
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Bayer process. The Bayer process is the principal industrial means of refining bauxite to produce alumina (aluminium oxide). Bauxite, the most important ore of aluminium, contains only 30–60% aluminium oxide (Al2O3), the rest being a mixture of silica, various iron oxides, and titanium dioxide.