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Author: Subject: Collecting solid from filter paper after filtration - what is the proper technique?
beerwiz
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[*] posted on 26-5-2016 at 22:18
Collecting solid from filter paper after filtration - what is the proper technique?


I often filter high value solids with vacuum filtration and very often a lot of solids remain on the filter paper seemingly stuck in the fibers of the paper and can't really be scraped off.

What is the proper technique for removing all of the filtered product from filter paper?
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gdflp
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[*] posted on 26-5-2016 at 22:31


Two options here which I can think of. Firstly, use a glass frit instead which should trap less of your product, allowing for a better recovery. Be sure not to use metal objects to scrape the frit though as this can damage it.

Alternatively, if your product isn't heat sensitive, you can buy so "quantitative" filter paper. This type of filter paper is designed to burn with little or no ash residue, so you can simply place the filter paper in a crucible, and burn it off to recover the adhering product. Quite commonly used in settings such as inorganic analysis, where the salts such as oxides are not typically heat sensitive, but a near quantitative recovery is desired.

If neither of these are an option for you, just let the filter paper dry before trying to remove the product, and you should be able to recover the vast majority of it.




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beerwiz
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[*] posted on 26-5-2016 at 22:58


I tried to do that just now with a well dried piece of filter paper with embedded product. Using a metal spatula, I was able to scrape off some of the product but a lot remains embedded in the filter paper. About 50% of the poduct I scraped off contains paper fibers that came off. There must be another solution.

Maybe I should use non-paper filter like PTFE membrane disk filters? Recovery of nearly 100% of the product is mandatory due to the high value of the product.

Another idea that comes to mind is to soak the dried filter paper in a suitable solvent to wash the product out completely. Then evaporate the solvent and scrape off the product from the glass walls of the beaker or RBF.

[Edited on 27-5-2016 by beerwiz]
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JJay
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[*] posted on 26-5-2016 at 23:52


I've recovered some pretty valuable products before and have never really had a serious issue with that.... You might also try using a smaller Buchner with a smaller piece of filter paper. Also, you might try making bigger batches so you experience less mechanical loss (on a percentage basis).

[Edited on 27-5-2016 by JJay]




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Sulaiman
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[*] posted on 27-5-2016 at 00:02


I have two different types of paper filter disks from two different suppliers,
and the slow (#1) paper feels smoother and seems to trap less product than the medium (#3) papers.

Scraping the product off of the paper sounds like a bad idea (paper fibers as noted)
let your filter cake get really dry and usually only a stain remains in the paper.

OR
use a MUCH smaller filter, e.g. glass funnel with nail + small filter disc.
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DFliyerz
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[*] posted on 3-6-2016 at 11:02


This is a completely wild guess, but are the high value solids gold or PGMs that are to be re-dissolved in aqua regia? If so, just put the paper in the aqua regia and it will dissolve. If it's not to be re-dissolved, I just burn the filter paper while melting the metal.
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confused
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[*] posted on 3-6-2016 at 20:00


possible to redissolve the residue on the filter paper and recrystalise it?
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