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Author: Subject: Silver nitrate stain removal
itchyfruit
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[*] posted on 2-12-2011 at 09:54
Silver nitrate stain removal


Hi
Does anyone here have any tips on removing Silver nitrate stains from kitchen worktop/vinyl flooring?
I was thinking dilute Nitric acid, but have some concerns about damaging the worktop/floor.
Google came up with treating first with Potassium permanganate solution and then Sodium bisulphite solution, Ammonia apparently works, but sounds a little dangerous.
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mr.crow
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[*] posted on 2-12-2011 at 10:20


KMnO4 will make an even worse stain

Ammonia sounds like your best bet for dissolving silver ions. Why is it dangerous? Get some household ammonia for cleaning floors and open the window




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[*] posted on 2-12-2011 at 15:28


Ammonia it is then. Cheers
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lavenatti
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[*] posted on 8-12-2011 at 07:24


I've had some success with Sodium Thiosulfate.
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Arthur Dent
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[*] posted on 8-12-2011 at 10:29


Depends all on the surface. For synthetic surfaces that are normally resistant to acid, a dilute solution of Nitric acid and Hydrochloric acid poured dropwise in situ should do the trick. four drops of water, then one drop of Nitric acid, followed by three drops of Hydrochloric acid.

This dilute Aqua Regia solution should attack the metallic ions efficiently, while leaving vinyl/linoleum relatively intact. There may be some discoloration so try it on a hidden spot before proceeding.

You'll have to balance between choosing the original stain, or the discoloration that may be left, which one looks worse...

Robert

PS.: I would use this on wood surfaces, or granite/marble surfaces. I guess glazed ceramic tiles would be ok.


[Edited on 8-12-2011 by Arthur Dent]




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[*] posted on 8-12-2011 at 11:11


Ho Hum.
The stains are not due to silver ions (which are colourless).
They are due to metallic silver.
To dissolve that you need to oxidise it.
Potassium permanganate is a good oxidant, but it tends to stain things because it leaves MnO2 behind.
MnO2 will dissolve in bisulphite.

The nature of the stained surface limits what you can use to clean it (obviously).
Dilute nitric acid may not attack the vinyl floor too badly, but it would be a good idea to try an inconspicuous corner first.
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[*] posted on 18-2-2015 at 06:43


Hi all - new user.

I got up this morning and noticed brownish-black streaks all across a worktop. After a couple of red herrings, I realised that it was caused by silver nitrate (I had transferred it to a smaller container yesterday). I must have spilled a little and then wiped the surface, smearing it everywhere.

After reading this thread, I tried a combination which seems to have worked perfectly. I made a paste in a pestle and mortar of sodium percarbonate and 890 ammonia and scrubbed the worktop with it. NB You need very good ventilation if you don't want to be overcome by the ammonia fumes. The "theory" behind it, is that the percarbonate is an oxidant (it is an adduct of sodium carbonate and hydrogen peroxide) and should oxidise the metallic silver to the Ag+ ion. This then forms a soluble complex ion with the ammonia - [Ag(NH3)2]+, which can easily be washed away.

It is possible that (a) it would have worked with more dilute ammonia (safer, but possibly slower) and (b) that hydrogen peroxide solution might have worked instead of the percarbonate (but I didn't have any hydrogen peroxide).

I hope that this helps somone in the future,

Gary
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[*] posted on 18-2-2015 at 07:54


The best I've ever used was potassium cyanide.

Warning: Cyanides are extremely toxic and must not be used without the proper safety precautions.
For these, please read a book. When dealing with dangerous chemicals one should never rely on advice from the Internet.

[Edited on 18-2-15 by Fulmen]




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[*] posted on 18-2-2015 at 07:57


Quote: Originally posted by Fulmen  
The best I've ever used was potassium cyanide.


Let's bring in a herd of elephants to scare away the lions!

You might want to explain CAREFULLY how KCN is used, and the safety precautions related to such use?

[Edited on 18-2-2015 by Bert]




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[*] posted on 18-2-2015 at 08:00


I know, I know. But it worked like nothing else.



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[*] posted on 18-2-2015 at 08:04


Once it's been reduced to elemental silver it's largely question of what's the substrate. Nitric acid would work but not if it damages the worktop. Quite dilute HNO3 would also work but take a lot of time.



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[*] posted on 18-2-2015 at 08:34


You want to leach the silver out. Any known material that leach silver should work in theory.
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[*] posted on 18-2-2015 at 08:49


Bert: Fair point, I've added a disclaimer. I just assumed that anyone in the possession of cyanides would know about the dangers, but one should never assume when it comes to dangerous chemicals.

To elaborate on this, it was more than 20 years ago when I was still an apprentice. I had a project for a professor, the old-school type, determining cyanides in spent anodes from aluminum production. So I was given a lab, 100g of KCN and was left to work on my own distilling off cyanides. So at that time I was already pretty comfortable with cyanides, so when he recommended it to remove a few stains I didn't even flinch. I think I just used a few grains of salt and a drop of water and rubbed the stains with a tissue. Of course I used nitrile gloves and washed off the bench thoroughly afterwards, other than that I don't think I took any special precautions.





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[*] posted on 18-2-2015 at 09:14


Just seen all of the replies!

I think I'd steer clear of cyanides myself (even if I had any). I would have tried nitric acid if I'd had any. I might get some 3% HNO3 as a general purpose reagent. I wish that the 69% was still legal. I've noticed that "pH Down Grow" is still being advertised by the hydroponics (ha ha) stores, which is 38% nitric acid, but I can't see how it's legal (unless I've misunderstood the explosive precursors regulations).

Cheers,

Gary
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[*] posted on 21-6-2017 at 00:22


Ammonia or Sodium Thiosulfate seems like an good option.

Also potassium cyanide is a great option too but make sure to use safety precautions




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[*] posted on 21-6-2017 at 00:38


Quote: Originally posted by ralphbrown1  
Ammonia or Sodium Thiosulfate seems like an good option.

Also potassium cyanide is a great option too but make sure to use safety precautions

Ah, you responded to a two year old thread, but because it's your first post, we can cut you some slack.

KCN sort of worked on the bathroom sink, but the stains are just lighter-colored; they're still there. If you're doing silver plating youll probably have KCN anyway, since it's necessary for that, and you'd probably be familiar with its singular danger: whatever you do, DON'T PUT IT IN ACID! EVER! As long as you don't do that, or leave it where someone else might somehow get acid on it without knowing what it is, you'll be good. That rule also extends to stomach acid.




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[*] posted on 21-6-2017 at 05:34


"The use of Iodine followed by Sodium thiosulphate to remove stains has been found to work also." Maybe the iodine picks up metallic silver if that's the culprit.
http://www.techknow.org.uk/wiki/index.php?title=Removal_of_S...

Here it says a strong solution of potassium iodide or alcoholic iodine solution followed by ammonia water.
https://books.google.com/books?id=3-1xAAAAIAAJ&pg=PA427&...

I wonder if this is any good?
https://www.google.com/patents/US3434796



[Edited on 21-6-2017 by Morgan]
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[*] posted on 22-6-2017 at 03:35


The use of ammonia to address a silver presence I find interesting!

Yes, it works forming a complex ion with ammonia, namely [Ag(NH3)2]+, as was noted above. But let's assume that it was not entirely washed away.

This is where the fun starts. The complex dehydrates and can breakdown into Ag3N and some Ag2NH. The latter silver nitride has a more common name, 'fulminating silver', that anyone who has done silver mirrowing knowns is a terrifying explosive compound to be avoided!

I would think such an event is somewhat rare, but when it does form and explodes, it can be a noteworthy event.

As such, I would not recommend any protocol involving mixing silver (especially a Ag-Ag2O combination) with excess ammonia and allowing to dry in the presence of an energy source (heat - chemically induced or otherwise, sunlight,...).

See prior comments, research and links at https://www.sciencemadness.org/whisper/viewthread.php?tid=70...

[Edited on 22-6-2017 by AJKOER]
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[*] posted on 22-6-2017 at 04:26


This is no issue in cleaning small patches of skin. The amount of silver in the dark stains is incredibly low. When the stain is removed, most of it is dissolved and is removed. The amount, remaining in the skin, is so low that there is ZERO risk of explosion.

The risk of explosion indeed is a very real one, when one allows ammoniacal solutions of silver to stand for a longer time. Even a solution with just a few tenths of percent of silver can form highly explosive crusts. The stains on skin, however, can be 100% safely cleaned with ammonia (at least from the point of view of risk of explosion, other risks, such as allergic reactions still exist).




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