Hi all
some time ago, thread about silver de-plating water cell attracted my attention. I read about it way ago and thought - hey, such a simple and clever idea. And instantly forgot about it, as I was doing some more important stuff. But now, when all of my refining stopped... I thought that I will try to experiment with something. Something I can manage without fumehood and a lab. And then I re-discovered water cell.
Way ago, my partner in refining processed larger batches of silver plated brass/copper scrap. He used electro-deplating in ammonia solution with subsequent drop of silver. This method works quickly, but is not selective and copper is also dissolved in substantial amounts.
It let me thinking about other ways. So I dug out some silver plated copper and brass and started some experiments. I tried original water cell, with just plain water. It kinda worked, but whenever the plating was removed and base metal exposed, excessive copper hydroxide was formed and deplating started to be wasteful. Not to mention it was painfully slow.
I then gave it second thought and try some more scientific approach - we need to make better electrolyte than plain water, and we need to somehow manage formation of that copper hydroxide junk. Starting slowly, my first "kitchen" choice was vinegar - yes, silver acetate is reasonably soluble in water and copper acetate also is. This kinda improved the outcome, but again - when silver coating was removed somewhere to base metal, reaction of the brass/copper underneath was way faster than that of silver, and even overpotential of 12+V cannot help to overcome this in any meaningful way.
Then I tried neutral electrolytes like sodium sulfate and sodium nitrate - without any appreciable effect. Hydroxides formed and copper was preferentially dissolved if it could be. No surprise in the end, as copper is more reactive. Dilute sulfuric acid speeded the process substantially, but again, deplating of silver was not the primary outcome of the experiment.
Then I tried something else. Sulfuric gold stripping in concentrated sulfuric is well known and working. So why not silver ? And why use concentrated acid, if the copper is passivated from like 50% up ?
I gave it a shot. 54 % sulfuric acid, voltage from like 4 to 12 V worked equally well (of course higher voltage faster). On the de-plated areas it start to bubble (persumably oxygen), and de-plating is nicely visual. No insoluble hydroxides. Also, I did not notice much of the blue colour (if any at all - but this can be misleading since copper sulfate isn´t that much coloured in comparison with other copper salts) from dissolved copper/brass, so I can say it does not dissolve too much of the base metal. Retention of silver in the solution is low (salt solution made some milky cloud, but not real precipitate) majority is "plated" on the cathode as fine, loose blackish powder. Most probably it isn´t Ag2O, since it does not redissolve in sulfuric acid after the current is stopped.
Once the silver is deplated, reaction do not go further much, and underlaying copper or brass is fairly intact. I did not measured the zinc percentage in the brass I deplated, But I assume it wasn´t that high.
However, I need to somehow test it further and do more research about electrochemistry of fairly concentrated sulfuric acid, as electrolysis is one way how to prepare peroxodisulfuric acid from more concentrated sulfuric acid. Peroxodisulfuric is fierce oxidizer. No unusual reactions observed so far, and in theory base metal should react with such oxidizer, so I am positive this isn´t the case... But I want some additional proof. Until then, be careful with it.
Any experiments and broadening the knowledge is welcomed. Setup I use is very simple, just some power supply, two clips and some pot with a bit of sulfuric acid. I want to play around with it more - I like that there is no NOx production as with sulfuric/nitric approach, no need to use hot concentrated sulfuric acid and no annoying hydroxides formed.
Photo of deplated samples of copper and brass below.
some time ago, thread about silver de-plating water cell attracted my attention. I read about it way ago and thought - hey, such a simple and clever idea. And instantly forgot about it, as I was doing some more important stuff. But now, when all of my refining stopped... I thought that I will try to experiment with something. Something I can manage without fumehood and a lab. And then I re-discovered water cell.
Way ago, my partner in refining processed larger batches of silver plated brass/copper scrap. He used electro-deplating in ammonia solution with subsequent drop of silver. This method works quickly, but is not selective and copper is also dissolved in substantial amounts.
It let me thinking about other ways. So I dug out some silver plated copper and brass and started some experiments. I tried original water cell, with just plain water. It kinda worked, but whenever the plating was removed and base metal exposed, excessive copper hydroxide was formed and deplating started to be wasteful. Not to mention it was painfully slow.
I then gave it second thought and try some more scientific approach - we need to make better electrolyte than plain water, and we need to somehow manage formation of that copper hydroxide junk. Starting slowly, my first "kitchen" choice was vinegar - yes, silver acetate is reasonably soluble in water and copper acetate also is. This kinda improved the outcome, but again - when silver coating was removed somewhere to base metal, reaction of the brass/copper underneath was way faster than that of silver, and even overpotential of 12+V cannot help to overcome this in any meaningful way.
Then I tried neutral electrolytes like sodium sulfate and sodium nitrate - without any appreciable effect. Hydroxides formed and copper was preferentially dissolved if it could be. No surprise in the end, as copper is more reactive. Dilute sulfuric acid speeded the process substantially, but again, deplating of silver was not the primary outcome of the experiment.
Then I tried something else. Sulfuric gold stripping in concentrated sulfuric is well known and working. So why not silver ? And why use concentrated acid, if the copper is passivated from like 50% up ?
I gave it a shot. 54 % sulfuric acid, voltage from like 4 to 12 V worked equally well (of course higher voltage faster). On the de-plated areas it start to bubble (persumably oxygen), and de-plating is nicely visual. No insoluble hydroxides. Also, I did not notice much of the blue colour (if any at all - but this can be misleading since copper sulfate isn´t that much coloured in comparison with other copper salts) from dissolved copper/brass, so I can say it does not dissolve too much of the base metal. Retention of silver in the solution is low (salt solution made some milky cloud, but not real precipitate) majority is "plated" on the cathode as fine, loose blackish powder. Most probably it isn´t Ag2O, since it does not redissolve in sulfuric acid after the current is stopped.
Once the silver is deplated, reaction do not go further much, and underlaying copper or brass is fairly intact. I did not measured the zinc percentage in the brass I deplated, But I assume it wasn´t that high.
However, I need to somehow test it further and do more research about electrochemistry of fairly concentrated sulfuric acid, as electrolysis is one way how to prepare peroxodisulfuric acid from more concentrated sulfuric acid. Peroxodisulfuric is fierce oxidizer. No unusual reactions observed so far, and in theory base metal should react with such oxidizer, so I am positive this isn´t the case... But I want some additional proof. Until then, be careful with it.
Any experiments and broadening the knowledge is welcomed. Setup I use is very simple, just some power supply, two clips and some pot with a bit of sulfuric acid. I want to play around with it more - I like that there is no NOx production as with sulfuric/nitric approach, no need to use hot concentrated sulfuric acid and no annoying hydroxides formed.
Photo of deplated samples of copper and brass below.
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