# Stripping Ag from Cu using Electrolytic Sodium Thiosulfate



## goldsilverpro (Jan 30, 2014)

For many years, I've seen this method in the plating literature but have never tried it. If it works well, it might solve the problems with stripping silver from copper.

It is covered in patent 2758074. Here's some excerpts from the patent:


> The surface is immersed in a water solution of sodium thiosulfate and electrolyzed anodically, that is, the silver surface is made anodic with respect to the solution. The concentration of the sodium thiosulfate solution is not critical. Generally any concentration between about 50 and 500 gm. per liter based on anhydrous sodium thiosulfate provides satisfactory results. A concentration between about 150 and 200 gm. per liter is preferred since it allows relatively rapid electrolytic action and a relatively high degree of control. Current densities of up to 20 amperes per square foot of surface area may be utilized. The electrolysis is continued until substantially all the silver is removed from those portions 12 of the surface as shown in Figure 2 not covered with resist.
> 
> A particular feature of the invention comprises deplating the silver film in a solution of sodium thiosulfate. This solution deplates silver relatively rapidly at relatively low temperatures such as room temperature. It does not build up an undesirable layer of insoluble material on the silver surface being deplated.


Patent attached.

It says that the temperature should not exceed 170F but that it does work at room temp. I have no idea how much silver it will dissolve before it stops working - probably quite a bit. Were I to set up an experiment with this, I would probably first try using a SS sheet as the cathode, operate at 10 amps/square foot and room temp.

A potential problem I can see is that the thiosulfate might break down and form black silver sulfide at the cathode - EDIT: I am beginning to feel that is a good thing.


----------



## 4metals (Jan 30, 2014)

So you are suggesting an anodic plating barrel full of plated silverware in the electrolyte. A lot of refiners get drums of silver plated stuff they toss into drums and never touch. As long as they don't have to pay a customer for each batch it can work. I guess you could figure the silver content after each different batch and pay on that but it may be more trouble than it's worth. I think escrap would have contact problems.


----------



## Lou (Jan 31, 2014)

GSP, you're right: much of the deposit from thiosulfate solutions is heavily contaminated with Ag2S. Thiosulfate is not nearly as redox stable as plain ol' sulfate.

I'd plate it onto steel wool and heavily flux it with silica, carbonate, and borax to remove the iron.


----------



## goldsilverpro (Jan 31, 2014)

Or you could precipitate Ag2S from the solution with Na2S, collect all the rinsed sludges together, from both the cathode and the precipitation, and melt them in a gas crucible furnace with borax and several lengths of rebar long enough to stick up out of the crucible. That's how I always did Ag2S. To me, it's the simplest way.

I was thinking about plated silverware, but only on a bucket scale - hobbyist size. The silverware could be wired or hung with copper wire. 

Like I said, I've never tried this and, probably never will. In my favorite old plating book, "Modern Electroplating", 3rd edition, it is listed as a method in the stripping chapter and I keep running into it.

If I were to use a large silver stripping setup with a barrel plater, I would most certainly use a solution of about 150g/l NaOH + 45g/l NaCN with a couple of 300 series SS sheet cathodes, one on each side of the barrel, at about 3 or 4 volts. The high NaOH prevents attack on the copper and, as the silver dissolves, it simultaneously plates out on the cathodes. The solution can be used almost indefinitely with occasional analysis and additions of the chemicals.


----------



## 4metals (Jan 31, 2014)

Cyanide would be easier but it also puts refiners in an entirely different compliance group with the EPA. The ability for NaOH to limit the copper dissolve is important, I wonder how much copper the thio would take up and still hold gold and silver. 

I love thiocyanate for cleaning up silver chloride encrustations from aqua regia stone removal and the recovery is easy but on scrap with copper base metal exposed things could get complicated.


----------



## Tub Buster (Feb 8, 2014)

I've only read the intro for this one. Seems like it could be a back door method of cyanidation.

http://link.springer.com/article/10.1134%2FS1070427210090156#page-1

Russian Journal of Applied Chemistry
September 2010, Volume 83, Issue 9, pp 1589-1592
On Electrochemical oxidation of thiocyanates in solutions for cyanidation of gold containing ores and concentrates
by T. A. Kenova, V. L. Kormienko, S. V. Drozdov

Abstract
Effect of hydrogen peroxide on the electrochemical oxidation of thiocyanate- containing solutions was studied.

Original Russian text published in Zhurnal Prikladnoi Khimii, 2010, Vol. 83, No. 9, pp. 1489–1492. [=4pp]


----------



## Geo (Feb 12, 2014)

this is a little experiment i tried.

[youtube]http://www.youtube.com/watch?v=VEorcsJQkZ0[/youtube]


----------



## goldsilverpro (Feb 12, 2014)

Good video, Geo. You and Ralph have this great Southern knack for doing good videos. Most importantly, both of you do the videos in real time, no matter how long it takes, and you continually talk and provide information. Of course, you need to do #2 to show us how to get the silver out. Have you tested the solution for silver? Manuel's copper wire method works well.

So now you have a silver sulfide sludge and a solution that probably has silver in it. If it does, I would probably drop the silver as a sulfide, as per Manuel. Then, I would use my rebar melting trick to collect all the sulfide from the silver and put it in the slag and then pour pure silver, assuming the thio didn't dissolve any copper. It's hard to be a silver refiner without at least a small gas-fired crucible furnace. You could probably be able to reuse the solution.

Looks like it works! Hurray for our side! Safe - Simple - Cheap - Room Temp. This could be the best thing since sliced bread for stripping silver from most anything, especially from silverware. Tons and tons of silver plated stuff out there that nobody really wants. If you have a good way to process it, you're in the driver's seat.

How much sodium thiosulfate per liter did you use? What was the total volume? How much current?


----------



## niteliteone (Feb 12, 2014)

Nice presentation 8) 
Are you able to get a 100% strip :?: 
How does it react with the base metals :?:


----------



## Geo (Feb 13, 2014)

well, the solution was made up for the gold plate stripping and that 50ml was a portion that i didnt use. the mixture was 10g of sodium thiosulfate to 300ml of water. the phone charger was 5v at 1 amp. base metal seemed to have been unaffected.










the wire looks completely stripped.


----------



## niteliteone (Feb 13, 2014)

Thanks Geo 8)


----------



## solar_plasma (Feb 13, 2014)

Very nice!!! Does anybody know, if this would work on Cu-Ni-Zn alloys? Some older silver plated flatware you find in europe is made of only Zn, - I guess the method wouldn't work on this material, would it? Because zinc powder is used for stripping photofixer, if I remember right.


----------



## Geo (Feb 13, 2014)

please dont accept this as fact but from my understanding, zinc is used as a cementing reagent. i dont think the base metal (even zinc) will effect the dissolution of the silver. it may actually help the conversion of the silver to silver sulfide. 

a few hours later.










as a side note, this does not work with gold plate. i tried a couple of different pieces of gold plated material and even though there was an electrolytic reaction, the pieces came out as pristine as it was when it went in.


----------



## goldsilverpro (Feb 13, 2014)

In the video, there was a black smut on the stripped wire. This could very well be silver sulfide.

A simple way to see whether or not it attacks copper, zinc, or other metals. Weigh a clean dry piece of the metal or alloy, itself, accurately and then electrolyze it as the anode for several minutes. Clean, dry, reweigh and compare the weights.

I doubt if it will attack German silver (nickel silver), the white copper alloy (Cu/Ni/Zn) used in flatware. I think that most of it has only about 20% zinc.

It might be interesting to see if just a solution of sodium thiosulfate and hydrogen peroxide will strip the silver, using no current. Simple immersion.


----------



## sharkhook (Feb 13, 2014)

That is very interesting. It might be time for me to study up on silver a bit more.


----------



## manduz77 (May 11, 2014)

sorry guys but I'm using google traslator for a better understanding of what I have to ask. 
I'm turning this forum for a while and 'are interested in various methods of refining both gold and silver.In this case I have the cable (including shield mesh) of copper heavily plated in sterling silver. What 's the way most' easy to get the silver metal.
I see the system in the video, someone has tried to do the whole process? Once you get Ag2S as Ag turn into? If you have a link or pdf documents or guides will gladly accept.THK


----------



## solar_plasma (May 11, 2014)

manduz77 said:


> sorry guys but I'm using google traslator for a better understanding of what I have to ask.
> I'm turning this forum for a while and 'are interested in various methods of refining both gold and silver.In this case I have the cable (including shield mesh) of copper heavily plated in sterling silver. What 's the way most' easy to get the silver metal.
> I see the system in the video, someone has tried to do the whole process? Once you get Ag2S as Ag turn into? If you have a link or pdf documents or guides will gladly accept.THK



http://goldrefiningforum.com/~goldrefi/phpBB3/index.php


----------



## yar (May 31, 2014)

http://goldrefiningforum.com/phpBB3/viewtopic.php?f=50&t=20362

I found this by Manuel very interesting. Goes together well with the topic at hand


----------



## yar (May 31, 2014)

Sorry wrong linq.... Here it is.
http://goldrefiningforum.com/phpBB3/viewtopic.php?f=50&t=6167


----------



## danieldavies (Jul 28, 2016)

hello members
i have been experimenting with geo's stripping technique on silver plated steel. i was shocked how fast it strips. 
i made a solution of 20 grams of sodium thiosulphate and 600ml of tap water. I used a stainless steel cathode which was connected up to a 9v AC adapter plug. It runs at 1.5A. 
it took about 10 seconds to strip each item. 
I will try and post a few pictures


----------



## danieldavies (Jul 28, 2016)




----------



## danieldavies (Jul 28, 2016)




----------



## the iron dwarf (Jul 30, 2016)

have a lot of Ag on aluminium, anyone know if this will work?
I will try a small piece as well as testing a plain piece of aluminium and report back here unless someone knows one way or the other.
will be a few days before my Sodium Thiosulphate arrives.


----------



## g_axelsson (Jul 30, 2016)

the iron dwarf said:


> have a lot of Ag on aluminium, anyone know if this will work?
> I will try a small piece as well as testing a plain piece of aluminium and report back here unless someone knows one way or the other.
> will be a few days before my Sodium Thiosulphate arrives.


Why not just use nitric acid if it is silver on aluminium.

Göran


----------



## the iron dwarf (Jul 30, 2016)

can get nitric of about 3% here in the UK


----------



## danieldavies (Jul 31, 2016)

the iron dwarf said:


> have a lot of Ag on aluminium, anyone know if this will work?
> I will try a small piece as well as testing a plain piece of aluminium and report back here unless someone knows one way or the other.
> will be a few days before my Sodium Thiosulphate arrives.



it should work on aluminium. You will be left with silver sulphide which settles nicely at the bottom.


----------



## the iron dwarf (Jul 31, 2016)

will try a small piece after testing unplated aluminium to see if it is attacked as soon as supplies arrive


----------



## richard2013 (Aug 5, 2016)

Will these work on gold plating? I am still trying to find sodium thiosulfate in my area


----------



## the iron dwarf (Aug 6, 2016)

richard2013 said:


> Will these work on gold plating? I am still trying to find sodium thiosulfate in my area


a post by GEO above states ......
"As a side note, this does not work with gold plate. i tried a couple of different pieces of gold plated material and even though there was an electrolytic reaction, the pieces came out as pristine as it was when it went in."


----------



## the iron dwarf (Aug 9, 2016)

looks like after a while it attacks the aluminium, got some white crystalline bit in the mud and on the aluminium, going to put the mud through a sieve to see if that gets it out and will do the aluminium separately in future and more carefully, brass seems to be ok 
have been working with about 500ml mostly then pouring the liquid including the mud into a larger container to settle and when reasonably clear decant off enough into a beaker to do more.
now I have got quite a bit of the mud so am filtering that as decanting was getting more difficult, will dry out the mud and continue.
I dont know if aluminium will cause a problem later or how to deal with it, I may recover what I can until I have enough to make refining it worthwhile and in the meantime read what I can.


----------



## the iron dwarf (Sep 15, 2016)

using a phone charger I have checked the following and could not detect weight loss in the samples:

lead
tin
copper
brass
aluminium

so hopefully the silver will be reasonably pure and can later be further refined


----------

