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.