# Silver oxide recovery from a container



## refiner123 (Oct 16, 2020)

Hi

I bought a set of lab equipment from a bankrupt company. The lot had many useful pieces for newbie home refiner. (beakers, erlenmeyers, magnetic stirrer, buchner funnels, vacuum flasks, vacuum pump, etc)

When collecting the stuff I had bought, I found two thick walled large (~20 liter) plastic containers labeled silver oxide. I thought that those would be great for waste liquid storage so I picked them up rather than throwing to trash.

The containers did not contain any leftover liquid, but at least one of them contains large clumps of white powder.
The primary reagents used in this lab seemed to be hydrochloric acid, sodium hydroxide and sodium thiosulfate.
My guess is that the white powder could be silver chloride. (somebody rinsed silver oxide container with HCl?)
Both of the containers have black coating on their inside.

I am wondering whether there would be any reasonable way to recover the silver oxide layer from the containers before using them as waste liquid containers. Even though the layer is completely black, it is probably very thin.

I have thought out couple of options:
1) dilute nitric acid.
Nitric will dissolve silver oxide to silver nitrate. The challenge is how to rinse all the container walls without 
using large amount of acid. Nitric acid is expensive and expected amount of recovered silver is very small.
I can reuse some amount of leftover nitric acid to refine silver recovered via electrolysis.
Nitric rinse creates NOx gas and due to the size of these containers it might be hard to do this rinse safely.

Nitric won't dissolve any silver chloride clumps from the bottom of containers.
I probably won't be able to get all of the assumed silver chloride out of the containers before the acid rinse.
Nitric acid rinse could contain both: silver nitrate and silver chloride. Need to either separate them by filtering and process separately or convert all to chloride.

2) sulfuric acid
According to many sources, sulfuric acid reacts with silver oxide to create silver sulfate.
Ag2O + H2SO4 -> Ag2SO4 + H2O 

This reaction won't create toxic NOx fumes.
Dilute sulfuric acid is available with more reasonable cost as battery acid.

Can somebody enlighten me whether this reaction works with dilute sulfuric acid or does it require concentrated sulfuric acid?
Metallic silver requires concentrated sulfuric acid, but this should be oxide.

Silver sulfate is slightly soluble in warm water.
Would it be possible to recover the silver using small amount of battery acid diluted with warm water?
Silver sulfate can be converted to silver chloride with NaCl or HCl and processed with the assumed silver chloride.
I don't expect to recover pure silver with this method, but I could combine the recovered metallic silver to the silver recovered via electrolysis, which I will refine with nitric acid in the future.

Sulfuric won't dissolve assumed silver chloride clumps either, but if those end up in the same rinse water with silver sulfate, the remaining process is anyway the same.


3) hydrochloric acid
HCl will react with silver oxide to create silver chloride, but it is insoluble to water just like silver oxide.
--> does not help getting it off the walls of containers.

Which of these other forum members would other forum members consider?
(or can somebody hint of another method?)
Or would you just forget the silver oxide and try to get the assumed silver cholride out?


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## snoman701 (Oct 16, 2020)

whatever you do, test it on a tiny sample!


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## ION 47 (Oct 19, 2020)

Silver chloride when interacting with alkali will turn black, turn into silver oxide. Silver oxide can be reduced to metal in many ways: sugar syrup, formic acid, formalin ...


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## g_axelsson (Oct 19, 2020)

Test a sample to see if the white powder dissolves in water. Silver chloride is insoluble. It's an easy test to rule out many different chemicals.
Next step you could see if it turns purple on the surface if it is put in sunlight (UV-light). The light will break down the silver chloride into metallic silver and chloride. If the powder doesn't react on sunlight it isn't silver chloride.

Göran


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## refiner123 (Oct 19, 2020)

Hi

Thanks. I will do those tests for the assumed silver chloride once I am able to get it out from the container. (partially stuck to the bottom)
This forum has lots of information on how to convert silver chloride to metal (lye & sugar)

But what about the assumed silver oxide that has stuck to the HDPE plastic?
(black coating on the inside of the containers)
Any chances to dissolve and rinse it from the container walls with anything else than nitric acid?
Nitric acid has safety issues in this rinsing, and also it might be too expensive when compared to the possible amount of silver recovered.


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## ION 47 (Oct 19, 2020)

refiner123 said:


> Hi
> 
> Thanks. I will do those tests for the assumed silver chloride once I am able to get it out from the container. (partially stuck to the bottom)
> This forum has lots of information on how to convert silver chloride to metal (lye & sugar)
> ...



If it is silver oxide, then you can wash it off with an ammonia solution, then restore the silver with hydrazine or formalin. If metallic silver is reduced, then it can be done with КСrO3 or potassium permanganate with sulfuric acid.


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## Martijn (Oct 20, 2020)

After rinsing the white stuff out, and making sure its silver, I would try a very dilute nitric solution, just enough to cover the side when the container lays on its side(assuming its one with a screw cap) let one side leach out, turn, repeat until you have all sides clean. 
Add a drop of nitric if the reaction stops. 
Rinse out with distilled water, filter AgCl out and cement on copper. 
If it is silver, you already have silver chloride, you could convert it all to silver chloride and treat it all with NaOH and sugar. 
Martijn.


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## refiner123 (Nov 15, 2020)

Hi

Yes, the containers have screw caps. Thanks, I will try this method at some point. 
Just one more question: what do you consider as very dilute nitric solution? Would 5% work? (just trying to avoid wasting too much nitric to attempt with low expected yield)
I guess the reaction is slow enough that I could just close the caps and let NOx gas remain within the container without overpressuring the container. (hopefully NO2 will react with water to create more HNO3 and reduce the amount of toxic gas emissions)

The next thing is is that I need to figure out the most cost efficient way to acquire nitric acid to this process and also to refine silver recovered electrolytically from silver plated items.


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## Martijn (Nov 15, 2020)

Well a very dilute nitric will work very slowly. If you are plannning on making a silver cell, you can use a couple of ml more and use the solution to dissolve more silver with for your electrolyte.
The silver nitrate electrolyte needs a bit of free nitric anyway.
Keeping it dilute will prevent big orange clouds too. As you suspected, some of the NO(2/3/X?) gets regenerated into HNO3. Not much pressure build up to be expected from dissolving stains. Not much silver too. But its just to clean them, right? 
. 
The small amount of silver thats on the sides will probably not take more than a few ml to dissolve. 

Reuse or repurpose as much as you can. Something i've learned from butcher. So much possibilities. Waste is only waste until you have no more use for it. And then try to reclaim economically if possible. 

Martijn.


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## jadedalex (Oct 31, 2021)

Refiner, I wouldn't assume anything when purchasing used equipment. Like Goran said, take a small sample and test, test, test. Stannous test will turn test paper brown if Silver is part of the mix but without knowing what else is in the pails, this is guess work. If you have established beyond doubt that what you have is Silver, then use Nitric. You mentioned that you could seperate the Silver using hydrolosis, which I assume would mean a Silver cell. If you intend to use such a cell, add enough nitric to the pail to just cover the walls when the pail is on it's side, put a lid on it (vent holes open obviously), and slowly over the course of several days, rotate the pail along with the lid to soak the material off the walls. This needs to be done either in a properly vented fume hood with attached scrubbers or outside, which is really bad for the environment but I hope that you are doing these things correctly...Good luck.


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## Jado (Oct 31, 2021)

in HDPE I would avoid nitric. cutting the containers and scraping them out would be a lot less hassle to do safely.


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## Marcel (Nov 1, 2021)

In my experience Silver Oxide can be reduced by simply heating it above 80°C.
Another method is to use sulphuric acid. If you use dilute sulphuric acid, place the solution on a heater and heat it for around 30 minutes.
If using concentrated HSO4 (+96%), it will turn Silver Oxide to metallic silver within seconds. Safety precautions must be applied when working with concentrated HSO4


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