Σldritch
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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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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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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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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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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.
We're not banging rocks together here. We know how to put a man back together.
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CharlieA
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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!
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Ozone
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A centrifuge works well.
O3
-Anyone who never made a mistake never tried anything new.
--Albert Einstein
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