reverse electroplating of silver

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dreammicke

Member
Joined
Jul 9, 2011
Messages
15
hi can anyone help me I wonder if it will go at making sama thing with silver as with gold in sulfuric acid cell

and how to do so, what kind of liquid should be used and what should I use as catod and anode

Sincerely Mikael
 
I have never tried but I believe the concentrated stripping cell will work to collect silver, there will be a few more issues in recovery from the cell,and converting back to metal, I keep thinking I will try it someday.
 
Hello,

Since i've gained lots of experience from the forum, here comes time for payback :)

Reverse electroplating of silver from brass/bronze/copper(even stainless steel) is very well possible.
However, from my experience, i would bother with it only if you have heavily plated items, or lots of them(100kg +).
What i've seen: Industrial silver plating for electrical components: Small pieces(about 10 cm long, 2 cm wide, 0,5 cm thick) contain about 1-2% of silver by weight. Larger items(type of block 20x20x20) contain only about 0,2-0,6% of silver by weight.
Deplating is usually 95-99% effective.

Electrolyte should be concentrated sulphuric acid(at least 90% - recommending use of 96%), with a bit of nitric acid(often used 5%, but by my experince, 0,5-1% is ok for start, adding small amounts when necessary during operation)(electrolyte will thicken during operation - nitric acid will react with some tiny silver particles, forming AgNO3, sulphuric acid will immediately react with AgNO3 to form HNO3 and AgSO4 )

Cathode is lead bar - this is where silver deposits in form of small pure silver crystals(in conc. sulphuric acid more like silver-acid paste)(lead does not get attacked in sulphuric acid, diluted or concentrated) - do not use copper, i had bad experience with it.(Can't remember what was wrong, but something was) Make sure to connect with copper wire above the electrolyte surface(copper is not attacked by conc suplhuric acid, but will be attacked when on cathode).
Anode is deplated material - i usually used a cage made of copper wires and plates, into which i would shed to-be-deplated material. Connect with copper wire (copper does not get attacked by conc sulphuric acid on anode, and by my experience, the tiny bit of nitric in the electrolyte will have practically no effect on the copper cage.)

Make sure to construct the cage in a way which will allow you to easily remove from container and to shake it a bit(on the contact places(where one plated item touches other) the deplating will not be proceeding) - you need to rearrange items in the cage once during deplating. The smaller the items are, the more important this is.

Voltage used should be about 12-14 volts for start, after most item have been deplated, i often switch to 24-30 volts to speed finishing a bit.
When deplating 15kg of material, using 6 amps @12volts it takes usually about 20-30 minutes to get most silver down, with 1-2 more hours on 30volts to finish it.
If you plan on processing large amounts of plated silver, then be aware that to process 300 kgs of standard silver plated items(0,2 weight % of silver), it takes about 8 hours @ 50amps.

Temperature does not matter much, only take care to not go above 60 or 70 deg. celsius - when hot, sulphuric acid will attack copper.

When removing deplated items from electrolyte - pay attention - large cloud of SO2 will be released, also prepare some hook to suspend the cage on for at least 10 minutes, to allow electrolyte to flow and drip from deplated items.

Next post in 10 minutes
 
Rinsing:
Deplated items should be rinsed in clear water(maybe with a bit of hno3), save the rinsing water, it will contain some silver after time. Do not add chlorides to rinsing water - otherwise your deplated items will get covered in thin ugly layer of silver chloride(no need to worry about it though, loss of silver is minimal, but it looks ugly).
When you think it's time to process rinse water, add some copper bar to cement the silver out, or add HCl, to form AgCl precipitate.

Second rinsing is usually ok to pour down the drain. After that, treat deplated items with oil or colorless lackuer(to prevent formation of patina, or at least to slow it down a bit) If you don't care about how deplated items look like after time, just don't care.

Now comes the hard part - getting silver from electrolyte:
Silver will settle down to bottom of the electrolyte in 24-48 hours, however due to the thickness of conc. sulphuric acid, decantation is not a way to go.Best way would be to have a container with drain valve on the bottom of conical container, through where you would pour off the settled silver with a bit of electrolyte(works very nicely). Or use glass container to see where the silver is, and drain the electrolyte with hose.
After getting acid with silver, dilute and add NaCl, or HCl(to form AgCl from dissolved AgSO4), let settle and decant, or go directly to next step.

Silver treatement :
Collected silver should be treated with lye(if treating concentrated acid with lye - pay attention, extremely exothermic), AgSO4 will react to form Ag2O, while elemental silver will be untouched. Then rinse thoroughly(5 times or so), to remove NaSO4, and melt. Not much of a problem there.

Note that electrolyte contains dissolved 3,1g/liter of silver sulphate @20deg. celsius. This is why electrolyte is saved for next batches, never removed.(also why there will be seemingly no silver on the bottom after short operation)
The silver in electrolyte could probably be removed by diluting the electrolyte at least 5:1(water:electrolyte) and adding some NaCl, or HCl, to form AgCl. Never needed to do that, though.

Electrolyte hygroscopicity:
Electrolyte also gains water from atmosphere, so it will slowly dilute. By my experience, not much of a problem, - after 21 days of operation outside, 15liters of electrolyte was still very thick, guess concentration dropped from 96 to approx. 90%.
Regeneration of electrolyte can be done by adding oleum(100% sulphuric acid) - to increase concentration a bit.

If i forgot anything, or have something wrong, please notify me.

I'd try a small deplating cell(1 liter) at first, i learned a lot from test batch. Run 20kgs through it, and see how it behaves.

Best Regards
Marek "Moje"
 
Thank you for your help Marek "Moje"

I've got about 200kg of alpaca silver and I thought it's a good thing to start with because it's free and it does not hurt so much if it goes wrong

Best regards Mikael
 
You are most welcome.

For 200kg of material, i'd suggest 5 liter bath, you can load it with approx. 10kgs of material at once, and getting rid of the bath won't be that much pain :)
Note that distance between cage with items and lead cathode needs to be 3-5cm distant, that way you won't get short circuit by silver deposition. Also, as much lead cathode surface as possible helps(silver deposits on larger surface, growing slower towards cage with items).

Be aware though, that when silver is in alloy, it will either(guessing here, so it may or may not be correct):
1) take very long time to process, leaving base metals sponge behind(which is a problem, as it will rip to pieces and mix with silver on bottom (with high % of silver in alloy)
2) will not process, as when silver is removed from top layer, base metal sponge layer will practically stop electrolysis. (with low silver % in alloy)

But i've never processed much of silver alloy - when it was in alloy, and there was more than 10% of silver, i just went through nitric and cementation on copper.
Give it a try in small bath, you'll see what happens.

Good luck, and please notify me how the alloy went.
Best Regards
Marek "Moje"
 
Marek "Moje"

Thanks for the information I will keep you updated on the progress, but right now I'm still at the stage to read cm Hoke and ask if what I read and do not

understand properly so that there will not be dangerous for me or my surroundings

it is dangerous acids we use

mikael
 
Hello,

i want to build a cage with coopermesh and some cooper pipes for stabilization.
I wanna braze it with a brazing solder out of cooper and phosphor
(DIN 8513 L-Cu P6). Are there any problems with the phosphor? Thank you for
your help.
 
Hokes book just briefly mentions this silver stripping solution for plating industry; she discusses the recovery process for these solutions (page 80 in my book).
 
Ok now everything is clear, but there is one question. Could I filter the electrolyte to seperate the silver with a paper filter? And what lye do you use?
 
Frenchmen said:
Ok now everything is clear, but there is one question. Could I filter the electrolyte to seperate the silver with a paper filter? And what lye do you use?
Click to expand...

No chance of filtering electrolyte - concentrated sulphuric acid is very viscous(thick). Filtration would take ages, not mentioning that any paper in concentrated sulphuric will be carbonized(conc. sulphuric removes water from organics).

Your best bet to remove silver is to carefully decant the electrolyte using a hose.

You can use any lye, but sodium is cheapest, and works just fine.

Best Regards
Moje
 
Hi Moje,

thanks for helping. I got a nice toy called "pumpix" for a few bugs hope it works. My idea ist to fill the elctrolyte into a huge glas, so the silver can settle down and the elctrolyte can be decant.
 
Frenchmen said:
Hi Moje,

thanks for helping. I got a nice toy called "pumpix" for a few bugs hope it works. My idea ist to fill the elctrolyte into a huge glas, so the silver can settle down and the elctrolyte can be decant.
Click to expand...


Wow, a place that sell stuff for "bugs" :mrgreen:

Deano
 
Mojeho said:
Hello,

Since i've gained lots of experience from the forum, here comes time for payback :)

Reverse electroplating of silver from brass/bronze/copper(even stainless steel) is very well possible.
However, from my experience, i would bother with it only if you have heavily plated items, or lots of them(100kg +).
What i've seen: Industrial silver plating for electrical components: Small pieces(about 10 cm long, 2 cm wide, 0,5 cm thick) contain about 1-2% of silver by weight. Larger items(type of block 20x20x20) contain only about 0,2-0,6% of silver by weight.
Deplating is usually 95-99% effective.

Electrolyte should be concentrated sulphuric acid(at least 90% - recommending use of 96%), with a bit of nitric acid(often used 5%, but by my experince, 0,5-1% is ok for start, adding small amounts when necessary during operation)(electrolyte will thicken during operation - nitric acid will react with some tiny silver particles, forming AgNO3, sulphuric acid will immediately react with AgNO3 to form HNO3 and AgSO4 )

Cathode is lead bar - this is where silver deposits in form of small pure silver crystals(in conc. sulphuric acid more like silver-acid paste)(lead does not get attacked in sulphuric acid, diluted or concentrated) - do not use copper, i had bad experience with it.(Can't remember what was wrong, but something was) Make sure to connect with copper wire above the electrolyte surface(copper is not attacked by conc suplhuric acid, but will be attacked when on cathode).
Anode is deplated material - i usually used a cage made of copper wires and plates, into which i would shed to-be-deplated material. Connect with copper wire (copper does not get attacked by conc sulphuric acid on anode, and by my experience, the tiny bit of nitric in the electrolyte will have practically no effect on the copper cage.)

Make sure to construct the cage in a way which will allow you to easily remove from container and to shake it a bit(on the contact places(where one plated item touches other) the deplating will not be proceeding) - you need to rearrange items in the cage once during deplating. The smaller the items are, the more important this is.

Voltage used should be about 12-14 volts for start, after most item have been deplated, i often switch to 24-30 volts to speed finishing a bit.
When deplating 15kg of material, using 6 amps @12volts it takes usually about 20-30 minutes to get most silver down, with 1-2 more hours on 30volts to finish it.
If you plan on processing large amounts of plated silver, then be aware that to process 300 kgs of standard silver plated items(0,2 weight % of silver), it takes about 8 hours @ 50amps.

Temperature does not matter much, only take care to not go above 60 or 70 deg. celsius - when hot, sulphuric acid will attack copper.

When removing deplated items from electrolyte - pay attention - large cloud of SO2 will be released, also prepare some hook to suspend the cage on for at least 10 minutes, to allow electrolyte to flow and drip from deplated items.

Next post in 10 minutes
Click to expand...


Sir,
Thank you for sharing your experience. I am going to work out with silver plated copper wire. Where silver was plated using cyanide bath solution. Will there be any difference in the process suggested by you in the post?
Your prompt response will be highly appreciated.
Regards
Puneet Malpani
 
Dear Mojeho,
I wish to reverse electroplate silver plated copper wire. Silver plating was done on it using cyanide solution. So should i follow the same process suggested by you?
Your prompt response will be highly appreciated.
Can someone send me the hooke's book
I will be highly obliged
Regards
 

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