Bayer's Process for extraction of aluminium

In summary, the Bayer's process involves the formation of sodium aluminate and sodium silicate in the digester, followed by a cooling crystallization process that results in the production of aluminium hydroxide and sodium hydroxide. The water containing dissolved sodium aluminate is separated from the water containing dissolved sodium silicate through a process called clarification, which involves treating the mixture with lime and then filtering out the sodium aluminate solution.
  • #1
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In Bayer's process in the digester both water soluble sodium aluminate and sodium silicate are formed. After that my textbook says cooling the sodium aluminate it crystallizes to to give aluminium hydroxide and sodium hydroxide. My two questions are, one, in the digester alumina reacts with sodium hydroxide to form sodium aluminate and water, but when the heat and pressure are removed why does it give aluminium hydroxide and sodium hydroxide? Why not sodium hydroxide and alumina? And secondly, how is the water containing dissolved sodium aluminate separated from the water containing dissolved sodium silicate?
 
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  • #2
In Bayer's process, the sodium aluminate is formed in the digester, where alumina and sodium hydroxide react to form sodium aluminate and water. When the heat and pressure are removed, the sodium aluminate undergoes a cooling crystallization process to give aluminium hydroxide and sodium hydroxide. This occurs because the sodium aluminate is not stable at room temperature and pressure, and decomposes into aluminium hydroxide and sodium hydroxide. The water containing dissolved sodium aluminate is separated from the water containing dissolved sodium silicate by a process called clarification. In this process, the mixture of sodium aluminate and sodium silicate is passed through a series of tanks with screens and filters. The sodium silicate is too large to pass through the filters, so it is removed and the remaining solution is then treated with lime, which causes the dissolved sodium aluminate to precipitate out and settle at the bottom of the tank. The clarified liquid can then be decanted off the top.
 
  • #3
The reaction that happens in the digester is: Al2O3 + 2NaOH --> 2NaAlO2 + H2O When the heat and pressure are removed, the sodium aluminate undergoes a process called hydrolysis, which is a reaction between a salt and water. During this process, the sodium aluminate breaks down into its constituent parts of aluminium hydroxide and sodium hydroxide.To separate the water containing dissolved sodium aluminate from the water containing dissolved sodium silicate, the two solutions are usually treated with acids. The acid reacts with the sodium ions in the sodium aluminate solution to form sodium salts, which can then be separated from the silicate solution by filtration or other means.
 

What is Bayer's Process for extraction of aluminium?

Bayer's Process is a method for extracting pure aluminium from bauxite ore. It was developed in the late 19th century by Karl Bayer and has become the primary method for aluminium production worldwide.

What is the purpose of Bayer's Process?

The purpose of Bayer's Process is to separate pure aluminium oxide (alumina) from impurities in bauxite ore. This alumina can then be used to produce aluminium metal.

How does Bayer's Process work?

In the first step of Bayer's Process, crushed bauxite ore is mixed with a hot solution of caustic soda (sodium hydroxide) and heated under pressure. This dissolves the alumina and forms a solution known as sodium aluminate. In the second step, the solution is cooled and filtered to remove impurities. The remaining solution is then heated to evaporate water, leaving behind pure alumina. Finally, the alumina is heated in a smelting furnace with carbon to produce aluminium metal.

What are the advantages of Bayer's Process?

Bayer's Process is the most efficient and cost-effective method for extracting aluminium from bauxite ore. It also produces high-quality alumina that can be used in a variety of industrial applications. The process is also scalable, meaning it can be used for both large-scale and small-scale production.

What are the environmental impacts of Bayer's Process?

While Bayer's Process is generally considered to be a more environmentally friendly method for aluminium extraction compared to other methods, it still has some negative impacts. The process requires large amounts of energy and water, and can also produce waste products such as red mud, which can be difficult to dispose of properly. However, efforts are being made to mitigate these impacts through improved technology and sustainable practices.

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