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Residue and stain removal
Though there are several threads on some stain removal, this is a more general thread on removing common stains and residues from glassware,
equipment, the ground, etc. Here is also a variety of stain removal from Römpp’s Chemie Lexikon, Vol. 2, 7th ed, pgs. 1145-9. Feel free to add, especially if you know a tried and true method to remove aged silver stains from the cement.
Sulfur: modifications rhombic (e.g. most common sulfur, sulfur flowers, etc) and monoclinic dissolve in carbon disulfide or hot toluene (warm xylene
also said to work), though amorphous sulfur is not soluble in CS2, the monoclinic is also soluble in alcohol, benzene; but the rhombic is only
slightly soluble in EtOH, C6H6, ether according to the CRC Handbook. I’ve attempted to dissolve sulfur in conc. H2SO4 by heating, but it only
liquefied and then began to slowly vaporize. Not even heated Pirhana’s acid would dissolve it. According to: A Handbook of chemical technology
(1877), p. 199, great solvents are said to be CS2, coal-tar oil, benzol, and sulfur chloride.
Carbon: simple carbon residues will dissolve in a mixture of conc. H2O2 and H2SO4 (Pirahna’s solution). This mixture becomes very hot and eats and
oxidizes violently many organic materials, making it an explosion risk. It may or may not need a small amount of additional heat. A 1:1 volume
solution of conc. H2SO4 in 30% H2O2 works well. The risk of explosion increases with the concentration of peroxide used and reactivity of the other
compounds it may react with. Explosions have resulted when it was suspected that the presence of an organic solvent was responsible. Mentioned in The
Chemical News and Journal of Industrial Science (1908), XCVIII, p. 309 is that fuming HNO3 will attack amorphous carbon but not graphite, to form
water soluble humic acids.
Silver: silver stains are extremely difficult to remove from cement. I’ve used everything I can think of and basically no success. Several drops of
fuming HNO3 (d=1.52) let sit for a while, only etched the cement around it. Even using a metal filing tool, the stain remains. I tried one of the
methods from Römpp, one is putting so much I2 tincture or conc. KI solution on the stain and rubbing in until it turns yellow (AgI), this then washed
out with Na2S2O3 solution. The one I tried is the ratio mixture of 10-15 g glycerin and 90-85 g distilled H2O and has 75-80 g Na2S2O3 solubilized
under warming (30º) and stirring, then this covers the stain in the dark and cool for one day, then so much dropwise cold saturated aqueous oxalic
acid solution is added until the cloudiness begins showing sulfur formation. Römpp says this is used for textile goods, but I tried this method on
cement and it only caused a strange partial removal when dry. Concd. KCN solution is also said to work well against silver stains, but it did not work
on my stains. I’ve also used iodine tincture (with and without added dissolved I2) and thiosulfate method with no success. I have also used
dissolved I2 in some DMSO and then applied this to the stain (in the dark) and letting it sit for several hours. This worked slightly better than the
Na2S2O3/oxalic acid, but still only partly removed. Potassium iodocyanide (KI.4ICN.H2O), in or not in KI, is claimed to be an energetic remover of
silver stains, but no success here either. In German another name for AgNO3 is Höllenstein, no wonder, its stains are a hell to get out. U.S. Pat.
6726847 removes stains from DNA chips in ferro/ferricyanide mixture (0.1 M Na2S2O3, 1.0 M KOH, 0.01 M K3Fe(CN)6, 0.001 M K4Fe(CN)6), but likely it
will not even phase old stains in cement.
MnO2: stains left behind from MnO2, like from permanganates are said to best be removed with some sodium bisulfite (Photochemie und Beschreibung der
Photographischen Chemikalien, (1906), p. 296). U.S. Pat. 5205835 describes removal of MnO2 by solubilizing to manganous salts using reducing agents
which are usually sulfites, thiosulfate, hydroxylamine, etc. in a large excess and low pH (2.5 to 3.0). They use aqueous peracetic acid solutions to
remove MnO2 from denim. Aqueous mixture of sodium metabisulfite and thiosulfate does an excellent job on these stains in cement after sitting several
minutes, making it colorless. KMnO4 stains are said to be removed with oxalic acid, but it didn’t work on cement when I tried it with an aqueous
solution.
Rust (x FeO. y Fe2O3. z H2O): Many acids could be used. Phosphoric acid is used as rust cleaner, hydrofluoric acid in a dilute solution is also used.
Hydrochloric acid also works to dissolve rust. For avoiding the etching done by HF on e.g. tile or glass, U.S. Pat. 6297208 uses a mixture of ammonium
bifluoride, boric acid, oxalic acid, citric acid, etc. And for a rust remover not using harsh acids or fluorides see the compositions in e.g. U.S.
5468303, etc. A mixture of sodium pyrosulfite and hydrosulfite is also sold commercially as rust and iron stain remover.
I2: stains from iodine tincture, povidone iodine, Lugol’s solution, etc. For povidone iodine: U.S. Pat. 6309471 applies e.g. 23% aqueous potassium
salicylate (pH=12) from adding KOH to salicylic acid, with pretty good results. Iodine tincture: tried on cement stains: ethanol, acetone or
methylethyl ketone will do a rapid and great job of removing iodine tincture stains where rubbing or absorbtion is more or less needed, methanol and
isopropanol also work similar to EtOH. Anhydrous ether didn’t work (too volatile). Glycerol also didn’t work. Toluene works somewhat, but needed
to be scrubbed quite a bit. Dichloromethane works better than toluene. Chloroform, CCl4, CS2, C6H6, and GAA should also work. The sulfites
(pyrosulfite, hyposulfite) aqueous also work well on stains on clothing, but for cement, the organic solvents are much more suitable (they work much
more rapidly, although they don’t make it colorless like with the sulfites to iodide reaction).
The related threads:
Cleaning Inside of Flask
http://www.sciencemadness.org/talk/viewthread.php?tid=7277
Removing stubborn carbon from flask?
http://www.sciencemadness.org/talk/viewthread.php?tid=10008
iron mess to clean from rb flask
http://www.sciencemadness.org/talk/viewthread.php?tid=8960
Very stubborn stain in a flask
http://www.sciencemadness.org/talk/viewthread.php?tid=8841
Rust/denim (FeSO4)
http://www.sciencemadness.org/talk/viewthread.php?tid=6180
Removing KMnO4 stains
http://www.sciencemadness.org/talk/viewthread.php?tid=8319
Cleaning up iron(III)ferrocyanide stains
http://www.sciencemadness.org/talk/viewthread.php?tid=8093
Hot toluene: a great solvent for sulfur
http://www.sciencemadness.org/talk/viewthread.php?tid=3902
[Edited on 5-7-2008 by Schockwave]
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hankdavis
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For MnO2 stains, I get by with 1 part H2O2 to 2 parts vinegar. It's especially useful when invisible KMnO4 dust sabotages your entire counter top.
Also, you can sub in HCl or H2SO4 for vinegar in lesser amounts if you're feeling classy.
\"When you use a quote, put a famous name on the end, that\'s where all the jazz is!\" -- Jesus
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Formatik
National Hazard
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Thiourea solutions worked flawless against stubborn MnO2 stains on glassware. It turns brown stains instantly colorless.
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