Understanding Nucleation and Seeding in Precipitation Processes

[lenin_yuweh]

Hi!

I seem to be out of the loop at work. Too embarrass to ask my coworkers to explain it to me.

Can anyone explain what nucleation and seeding is?

Our process is basically a precipitation process where copper is precipitated by reacting Ca(OH)2 to Cu(OH)2. We have a sedimentation tank to separate the slurry from the filtrate. What I don't understand is how recirculation, pump sucks the slurry below and returns it to the calcium feeding tank, improve slurry formation. They mentioned nucleation and seeding enhancement. I don't get how "crystals" can form in a slurry or is a slurry considered a crystals?

 

[chemisttree]

Your slurry is likely a finely divided solid form of the Cu(OH)2 you seek. If these solids are crystalline in any way, they induce further solid to form on their surfaces. This causes the finely divided slurry form larger particles which are easier to remove by settling or filtration. So the initially formed very small particles induce the growth of a much larger particle. It is called "nucleation" or "seeding".

Pumping these growing "seed" crystals back to the Calcium feed tank let's those particles stay in contact with the copper solution longer thus allowing for larger crystal growth and a slurry that separates more quickly.