Dan's Question: Al(OH)3 in Bayer Process Precipitation

[danago]

Hi.
Im studying for a chemistry exam, and I am a bit unsure about something. As part of the electrochemistry component of the course i am required to know and understand various metal extraction processes. My book is fairly good for learning them, but one thing i am not sure about concerns the precipitation part of the bayer process.

Once the aluminate solution has been obtained, it is cooled and then seeded with pure aluminium hydroxide. I know the cooling is required to bring aluminium hydroxide out of solution, but why is the pure Al(OH)3 added? Whats the purpose of it?

Thanks in advance,
Dan.

 

[Vagrant]

Small particles (seeds) can trigger the separation of the dissolved material from the solvent or condensation of the vapor. In the solid form these seeds can lead to the formation of crystallites or even large single crystals.

 

[Blueshift5]

Hi Dan,

Great question! The addition of pure aluminium hydroxide (Al(OH)3) in the precipitation step of the Bayer process serves a few important purposes.

Firstly, the cooling and seeding process helps to control the size and shape of the crystals formed. By adding pure Al(OH)3, the seeded solution provides a surface for the crystals to grow on, resulting in more uniform and controllable crystal sizes. This is important for the subsequent steps in the extraction process.

Secondly, the addition of pure Al(OH)3 helps to increase the yield of the process. This is because the pure Al(OH)3 acts as a catalyst, promoting the precipitation of more Al(OH)3 from the solution. This results in a higher yield of the desired product.

Lastly, the pure Al(OH)3 also helps to remove impurities from the solution. These impurities can interfere with the extraction process and decrease the purity of the final product. By adding pure Al(OH)3, these impurities are removed from the solution, resulting in a purer end product.

I hope this helps to clarify the purpose of adding pure Al(OH)3 in the precipitation step of the Bayer process. Good luck on your exam!

Best,