Chemgineer - 11-7-2021 at 07:04
I'd like to clean some brown staining out of my sintered glass buchner funnel. It is a result of filtering Muriate of Potash and i'm guessing it is
sticky brown clay residue.
I have 50% Sulphuric Acid, 11% Hydrogen Peroxide, Anhydrous Sodium Bisulphate and 20% HCL.
What would be my best bet to make a good cleaning solution?
[Edited on 11-7-2021 by Chemgineer]
vmelkon - 11-7-2021 at 08:53
If it is an oxide/hydroxide/carbonate of some transition metal, then H2SO4 or HCl running through it would remove it.
If it is an organic material, you can make a weak piranha solution with your H2SO4 + H2O2 but you say it is some clay.
Sodium bisulfate is just NaHSO4 which is sort of like having H2SO4
Nitric acid would be worth a try. Add some KNO3 to H2SO4 if you don't have clean nitric acid.
You can also try bases, like a solution of NaOH or sodium hypochlorite but these slowly dissolve glass.
unionised - 11-7-2021 at 10:24
One of the best things to do is use water, flush it backwards through the funnel.
Belowzero - 12-7-2021 at 03:18
Grillcleaner or a percarbonate, perhaps your wife or gf might have some for you 
Often with labels as 'oxy action' or 'oxygen cleaner'
Grillcleaners often contain a or multiple hydroxides, they are suprisingly efficient, might corrode glass though.
[Edited on 12-7-2021 by Belowzero]
Chemgineer - 12-7-2021 at 05:17
Thanks for the suggestions, I actually have a few cleaning products.... i'm always reading what might be in them in case they are interesting.
Texium - 12-7-2021 at 05:33
The suggestions are good, but I would also add, I would recommend getting a classic porcelain Büchner funnel and filter papers for doing these sort
of filtrations that leave a lot of nasty, hard to clean residue. I’ve mucked about with cleaning glass frits too many times, and eventually realized
that I’d much rather be able to just throw the filter paper away instead of trying to figure out how to clean the funnel. I use a frit now only when
the precipitate is precious, or if I’m doing something like filtering a solution through a plug of silica gel, because that doesn’t work well in a
traditional Büchner funnel (and generally the nasties stay stuck to the silica and don’t make it through to the frit).
Fyndium - 12-7-2021 at 11:46
Organic solvent, acid, base and lots of water usually does the job. Like citric acid, sodium hydroxide, acetone. I've also flushed sodium percarbonate
through it by letting it drain by gravity.
Then there's the piranha of course.
For inert particles, backflushing helps. I put some water in the frit and push air through with hand pump backwards. Curtain of bubbles form, and the
water helps dislodge solids. Doing all these steps once or twice has gotten my frits shiny white without piranha every time.
Mateo_swe - 15-7-2021 at 09:11
I would also recommend a classic porcelain Buchner funnel and filter papers, especially when i know or suspect it will be hard to clean a fritted
funnel.
So easy to discard filter paper and easy cleaning, i prefer using them over fritted funnels.
Boiling water, ethanol, acetone, weak acid, sodium hydroxide solution, strong acid, piranha, something usually works.
Dont let sodium hydroxide be in contact with glass for long time as it slowly dissolves glass.