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Author: Subject: Filtering hydroxides, how to make them behave?
Σldritch
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mad.gif posted on 29-12-2018 at 16:48
Filtering hydroxides, how to make them behave?


I have had a lot of trouble vacuum filtering all kinds of insoluble hydroxides, they just clog filters or dissolve them, sometimes enough for the vacuum to make holes in them. Am i missing something or is there some trick to it?
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CharlieA
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[*] posted on 29-12-2018 at 18:22


Sometimes, stirring the suspension for a time, with or without heat, will result in the particles sticking to each other to form large particles which are easier to filter.
In removing fine particles from water/wastewater, sometimes an organic compound is added in small (ppm) levels which speeds up coagulation and makes filtration easier and more effective. Unfortunately it has been a while ~45 years, and I don't know what these compounds were called. "Coagulants" doesn't sound quite right, but I just can't remember.:(
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BromicAcid
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[*] posted on 29-12-2018 at 21:25


Charlie, the term you are thinking of is a flocculant.

@Σldritch - Filtering hydroxides is a notorious pain in the rear end. Aging of the precipitate to help with aggregation can help sometimes. But it also comes down to how it was formed. Form it from a concentrated solution and you'll get a different material (physically) than one make in a dilute solution. Strong vs. weak agitation. There are variations that can make the particles easier to filer. But on the whole it's just a mess.




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Tsjerk
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[*] posted on 30-12-2018 at 01:19


If you have access to one, or maybe you can build one from an old bicycle or something; centrifuging really help a lot by pelleting the hydroxide.
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Fulmen
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[*] posted on 30-12-2018 at 03:25


Precipitated insolubles can be hard to handle. Hydroxides can be especially bad as they sometimes form gels. If the compound forms ammonia complexes (for instance copper) you can precipitate by boiling off the NH3, this is a slow process that tends to form a much denser product.



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CharlieA
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[*] posted on 30-12-2018 at 17:40


Quote: Originally posted by BromicAcid  
Charlie, the term you are thinking of is a flocculant.

Thank you. I even helped run a pilot plant trying out different flocculants to clarify Missouri river water for a cooling tower at a nuclear plant, but just couldn't remember that term!:D
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Ozone
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[*] posted on 30-12-2018 at 18:22


A centrifuge works well.

O3




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