Maintaining my silver nitrate electrolyte solution

[rightmirem]

I do a lot of silver jewelry, including silver casting. I've just started experimenting with electrolytic silver refining, because all my scrap is too oxidized and crappy to cast anymore

I built a silver cell and it works pretty well.

• Stainless steel bowl as the cathode
• a titanium clip bridging the bowl to the negative alligator clip
• plastic basket with a nylon net to hold the small bits
• Fine silver pipe inserted into the scrap for the anode alligator clip
• 30 gram per liter pre-mixed silver nitrate solution

So, I knew I had some sterling in that mix, and expected the solution to fill with copper a bit - however, it very quickly went deep blue. I set the cell to 3.5 volts, which initially produced around 2.5 amps ... but the power supply quickly (<30 mins) auto-switched to constant current and volts dropped. So, I set it to a 2 amp constant current, after which the voltage stabilized at only 0.5volts.

I had an OK harvest (I guess) ... of about 5 grams silver flake in 16-ish hours of runtime.

My questions are these:

1. Is that a reasonable harvest for 16 hours runtime?
2. How can I preserve the silver ion concentration in my silver nitrate when purifying sterling?
3. Does the copper ion in the solution displace the silver ions, or just join it?
4. Just how "coppery" can the solution get before it stops plating silver out? (I don't mind so much if it has copper residue in the crystals. I'm just going to cast more rings with it. It doesn't need to be 99.999 pure or anything. )
5. How can I test the amount of silver ion in the solution electrically or chemically? Currently I'm trying the following experiment...
   • I weighed two small copper plates (about 22 grams total weight.)
   • I put the plates in the very blue silver ion solution, assuming any remaining silver will cement out on them.
   • Measure the plates tomorrow, to get the weight difference. and then calculate the silver using ΔWsilver=3.396×ΔWcopper.
     
     HOWEVER, I don't know if this is even a sane method, or whether my scales have the sensitivity to measure this (they are only accurate to the thousands place.)

Thanks for any help and advice!

 

[rightmirem]

I'm running a homemade silver refining cell with...

• 30 gram / liter silver nitrate solution (pretty clear. A tint of blue)
• Pure silver 999 anode (+) set in a plastic basket wrapped in a fine nylon net
  • The anode is the silver to be processed ~70 gram.
  • It has been melted and cast a half dozen times, so it's pretty crappy. Thats why I'm refining it.
  • But its not sterling.
• A stainless steel COTS bowl as the cathode.
  • A titanium connector connects the power supply (-) to the cathode. The titanium is not in contact with the silver nitrate solution.)
• 3.5 volts maintaining around 0.5 to 0.7 AMPs.

The process is going pretty well. Silver is plating out in sheets on the sides of the bowl (not as crystals but sheets...but maybe that's for a different discussion?) However, I get big chunks of grey metal in the anode basket. Grey "mud" also forms in the basket and inside the nylon filter (which I occasionally wash out into a collection pot with distilled water.



There's clearly some silver in there, that has broken off the anode silver. But the chunks I'm referring to don't look like refined silver, and they form in chunks (like mud balls.) I can crush them easily with my fingers.

• Are these silver that is not plating out and just sluffing off the anode to into a mud that clumps together?
• Or maybe highly oxidized silver?
• Or leftover flux (I use pure boron powder.)
• Contaminating metals (iron?)
• Or something else?
• How can I test the substance (I've ordered some silver testing acid, but it's not here yet )

I'd like to find out for potential recovery or proper disposal.

 

[Yggdrasil]

I'm running a homemade silver refining cell with...

• 30 gram / liter silver nitrate solution (pretty clear. A tint of blue)
• Pure silver 999 anode (+) set in a plastic basket wrapped in a fine nylon net
  • The anode is the silver to be processed ~70 gram.
  • It has been melted and cast a half dozen times, so it's pretty crappy. Thats why I'm refining it.
  • But its not sterling.
• A stainless steel COTS bowl as the cathode.
  • A titanium connector connects the power supply (-) to the cathode. The titanium is not in contact with the silver nitrate solution.)
• 3.5 volts maintaining around 0.5 to 0.7 AMPs.

View attachment 64722
The process is going pretty well. Silver is plating out in sheets on the sides of the bowl (not as crystals but sheets...but maybe that's for a different discussion?) However, I get big chunks of grey metal in the anode basket. Grey "mud" also forms in the basket and inside the nylon filter (which I occasionally wash out into a collection pot with distilled water.

View attachment 64721

There's clearly some silver in there, that has broken off the anode silver. But the chunks I'm referring to don't look like refined silver, and they form in chunks (like mud balls.) I can crush them easily with my fingers.

• Are these silver that is not plating out and just sluffing off the anode to into a mud that clumps together?
• Or maybe highly oxidized silver?
• Or leftover flux (I use pure boron powder.)
• Contaminating metals (iron?)
• Or something else?
• How can I test the substance (I've ordered some silver testing acid, but it's not here yet )

I'd like to find out for potential recovery or proper disposal.

I moved this post to your other post since it is the same call and process.

 

[Yggdrasil]

I'm running a homemade silver refining cell with...

• 30 gram / liter silver nitrate solution (pretty clear. A tint of blue)
• Pure silver 999 anode (+) set in a plastic basket wrapped in a fine nylon net
  • The anode is the silver to be processed ~70 gram.
  • It has been melted and cast a half dozen times, so it's pretty crappy. Thats why I'm refining it.
  • But its not sterling.
• A stainless steel COTS bowl as the cathode.
  • A titanium connector connects the power supply (-) to the cathode. The titanium is not in contact with the silver nitrate solution.)
• 3.5 volts maintaining around 0.5 to 0.7 AMPs.

View attachment 64722
The process is going pretty well. Silver is plating out in sheets on the sides of the bowl (not as crystals but sheets...but maybe that's for a different discussion?) However, I get big chunks of grey metal in the anode basket. Grey "mud" also forms in the basket and inside the nylon filter (which I occasionally wash out into a collection pot with distilled water.

View attachment 64721

There's clearly some silver in there, that has broken off the anode silver. But the chunks I'm referring to don't look like refined silver, and they form in chunks (like mud balls.) I can crush them easily with my fingers.

• Are these silver that is not plating out and just sluffing off the anode to into a mud that clumps together?
• Or maybe highly oxidized silver?
• Or leftover flux (I use pure boron powder.)
• Contaminating metals (iron?)
• Or something else?
• How can I test the substance (I've ordered some silver testing acid, but it's not here yet )

I'd like to find out for potential recovery or proper disposal.

Welcome to us.
This is broken off pieces of Silver and slimes of Silver and other metals from your anode.
Do you have pictures of your anode and plated Silver?

 

[4metals]

• Are these silver that is not plating out and just sluffing off the anode to into a mud that clumps together?
• Or maybe highly oxidized silver?
• Or leftover flux (I use pure boron powder.)

All of the above. The most abundant metal in Silver slimes is Silver. I have had success at lowering the Silver percentage in the slimes by refining oxygen free anodes but the reward wasn't worth the effort.

I like to run Silver cells at 60 grams per liter. Maintaining the solution typically is done via a Volhard titration to determine the Silver in solution and the Silver is brought up to the desired strength with nitric acid additions. For smaller cells, like yours, the titration method is also labor intensive for such a small cell.

 

[adam mizer]

Also what is the purpose of titanium connector?
I think this is a reduction to your current used as an electrical connection lower conductivity and more resistance to flow.

 

[rightmirem]

Thanks to all for the welcome, and the responses. Answers and pictures...

@adam mizer
Honestly, I'm just using the titanium connector because (with the lid in place) I can't clip the alligator (-) directly to the bowl, I tried making a stainless steel connector, but the power drop was the same and it fit like crap I happened to have titanium clip I use for soldering silver, that fit very nicely.


I think I've figured out the voltage drop. I think it's as simple as the silver nitrate solution being depleted near the anode. In this last run, if I came in after the voltage drop and just shook the anode, the voltage came back. I started running the cell on a vibrating table, and the voltage stopped dropping (presumably because the electrolyte was getting constantly circulated.

===

@Yggdrasil and @4metals

Here's what things look like now. I'm creating just a BOATLOAD fo slimes. I'm curious if it's the stainless steel bowl. In one of the following pics, I used the same solution with the same anode, but with a graphite block as the cathode. I got a lot of silver collection, and some slime/chunks, but the solution remained nearly clear.

Compare that with the pic from the stainless steel bowl, which looks like a swamp!

Anode (after rinsing with distilled):


Cathode bowl (after draining, before rinsing):


Plated silver after being rinsed:

Which made literally like a liter of muddy rinse water:


Cell using silver nitrate solution, same anode, but a graphite block as cathode (had been run for 16 hours. NOTE: Thats a graphite rod which touches the silver anode):

 

[Master Nater]

your 'plated silver' should rinse perfectly clear. if it is not, you either have a hole in your anode basket that is letting contaminants into your cell, or you are running such contaminated material that your electrolyte is no longer running cleanly and you should do some refining before putting this material into your cell. perhaps not changing out your electrolyte often enough? what are you using for an anode filter? it looks extremely porous in your photo. does it have holes burnt in it from the silver burning it's way into the basket, in the event of a dead electrical short?

 

[Yggdrasil]

Thanks to all for the welcome, and the responses. Answers and pictures...

@adam mizer
Honestly, I'm just using the titanium connector because (with the lid in place) I can't clip the alligator (-) directly to the bowl, I tried making a stainless steel connector, but the power drop was the same and it fit like crap I happened to have titanium clip I use for soldering silver, that fit very nicely.

View attachment 64743
I think I've figured out the voltage drop. I think it's as simple as the silver nitrate solution being depleted near the anode. In this last run, if I came in after the voltage drop and just shook the anode, the voltage came back. I started running the cell on a vibrating table, and the voltage stopped dropping (presumably because the electrolyte was getting constantly circulated.

===

@Yggdrasil and @4metals

Here's what things look like now. I'm creating just a BOATLOAD fo slimes. I'm curious if it's the stainless steel bowl. In one of the following pics, I used the same solution with the same anode, but with a graphite block as the cathode. I got a lot of silver collection, and some slime/chunks, but the solution remained nearly clear.

Compare that with the pic from the stainless steel bowl, which looks like a swamp!

Anode (after rinsing with distilled):
View attachment 64744

Cathode bowl (after draining, before rinsing):
View attachment 64745

Plated silver after being rinsed:
View attachment 64747
Which made literally like a liter of muddy rinse water:
View attachment 64748

Cell using silver nitrate solution, same anode, but a graphite block as cathode (had been run for 16 hours. NOTE: Thats a graphite rod which touches the silver anode):
View attachment 64746

As Nater said, can younelaborate a bit more in detail on the design and construction of your cell.
The anode bag looks very coarse as he says.
There is definately something not right, so lets see if we can find the culprit.

 

[4metals]

I have never seen a cathodic deposit as nasty looking as your photo. And I have seen a lot of Silver cathode deposits. Are you sure you were refining sterling silver and not some other silver appearing metal like pewter?

 

[nickvc]

All of the above. The most abundant metal in Silver slimes is Silver. I have had success at lowering the Silver percentage in the slimes by refining oxygen free anodes but the reward wasn't worth the effort.

I like to run Silver cells at 60 grams per liter. Maintaining the solution typically is done via a Volhard titration to determine the Silver in solution and the Silver is brought up to the desired strength with nitric acid additions. For smaller cells, like yours, the titration method is also labor intensive for such a small cell.

4metals I ran sterling in my cell and just used the color of the electrolyte to:determine when to add more nitric but I believe Frugalrefiner had small samples of electrolytes at different levels of copper contamination to use as proofs for his cell to know when to add more nitric.

 

[rightmirem]

Thank you again for all the comments.

Answers follow (in no particular order.) There's some questions mixed in too

---

The anode silver
This chunk of silver was originally 99% pure silver, for sure. But it has been crucible melted and cast a half dozen times, so it may have a lot of flux and oxidation and crap in it. I would be surprised if it was this much crap however.

One clue that I think is important... is I ran this exact same piece of silver as the anode, the exact same anode bag, and using the exact same silver nitrate solution in a different cell that had a graphite block as the anode.

In this case, the solution remained clear, and there was very little (some, but not a lot) of slime.

The cell itself and graphite block cathode below.
NOTE: The anode is the same chunk of silver, touching a graphite rod, to which I attach the pos lead.

The picture of the cell on the left was after running overnight. The solution in the cell with the stainless steel anode starts to get murky after an hour.

Both the silver from the anode, and the copper from the solution plated out, which is why I didn't continue using this setup.

But this makes me think it's not the silver or the anode bag causing the issue.

---

The anode bag
The anode bag is crappy and way too porous. I got it from amazon. To make it a little less porous, I actually layered it four times. But since it didn't create cloudy solution in the above cell, I assumed it wasn't the problem. But I want to replace it anyway.

I was thinking of replacing it with COTS 100% nylon stockings (two or three layers.)

Q: Is that a dumb idea?

---

The anode basket
The anode basket is an old Tupperware plastic container, with holes drilled in to allow electrolytic solution to flow into it. I put the silver in the 4-layered filter bag, and set the bag in the basket. Could this be part of the problem (Plastic deterioration?)

Q:What should I be using as the anode basket?

---

The solution and nitric acid
The solution is a manufactured off the shelf silver nitrate solution. I did confirm it's a 30 gram per liter silver nitrate solution. I've ordered some silver nitrate powder to refresh it, but it hasn't come yet.

The solution has only been used twice (in steel cathode basket, and the above graphite cathode cell.) Maybe a total of 30 hours.

The problem is: I live in Germany. You can't buy or make nitric acid of a greater than 3% concentration without a license, which I do not have. I could probably get one, but I'm trying to avoid it I really don't have the facilities to make nitric acid safely.

Although I can buy a teeny bottle buy silver test acid. I don't know the nitric acid concentration, but if only a few drops are required, maybe I can use this (although it may come with some oxidizers mixed in.)

 

[Yggdrasil]

Thank you again for all the comments.

Answers follow (in no particular order.) There's some questions mixed in too

---

The anode silver
This chunk of silver was originally 99% pure silver, for sure. But it has been crucible melted and cast a half dozen times, so it may have a lot of lux and crap in it. I would be surprised if it was this much crap however.

One clue that I think is important... is I ran this exact same piece of silver as the anode, the exact same anode bag, and using the exact same silver nitrate solution in a different cell that had a graphite block as the anode.

In this case, the solution remained clear, and there was very little (some, but not a lot) of slime.

The cell itself and graphite block cathode...
View attachment 64751

Both the silver from the anode, and the copper from the solution plated out, which is why I didn't continue using this setup.

But this makes me think it's not the silver or the anode bag causing the issue.

---

The anode bag
The anode bag is crappy and way too porous. I got it from amazon. To make it a little less porous, I actually layered it four times. But since it didn't create cloudy solution in the above cell, I assumed it wasn't the problem. But I want to replace it anyway.

I was thinking of replacing it with COTS 100% nylon stockings (two or three layers.)

Q: Is that a dumb idea?

---

The anode basket
The anode basket is an old Tupperware plastic container, with holes drilled in to allow electrolytic solution to flow into it. I put the silver in the 4-layered filter bag, and set the bag in the basket. Could this be part of the problem (Plastic deterioration?)

Q:What should I be using as the anode basket?

---

The solution and nitric acid
The solution is a manufactured off the shelf silver nitrate solution. I did confirm it's a 30 gram per liter silver nitrate solution. I've ordered some silver nitrate powder to refresh it, but it hasn't come yet.

The solution has only been used twice (in steel cathode basket, and the above graphite cathode cell.) Maybe a total of 30 hours.

The problem is: I live in Germany. You can't buy or make nitric acid of a greater than 3% concentration without a license, which I do not have. I could probably get one, but I'm trying to avoid it I really don't have the facilities to make nitric acid safely.

With a business license you can buy Nitric I believe.
Muslin is what most use as anode bag.
A higher concentration Silver Nitrate is preferred I believe.
Do you have a sketch of your cell?
I can't quite wrap my head around the setup when looking at the graphite rod?
Are you using proper Stainless steel?
Low quality or ordinary steel, might dissolve and introduce Iron into the system.

 

[rightmirem]

Oh, and a separate question...

Im not real worried about getting 999 pure silver out of this. My goal is basically to refine the silver back to workable for casting. What started this entire project was that I tried to melt this silver chunk to cast it - and it simply would not melt again!

Point being...it doesn't matter to me if I get nice crystals. Which brings me to my question....

Q: Is there any reason I couldn't use silver as the anode and cathode. I.e. Dissolve the crappy silver at the anode, and just deposit pure (or more pure) silver ions back onto a chunk at the cathode?

As long as I end up with a pure (or more pure) chunk of silver I can melt, that's all I need.

 

[rightmirem]

With a business license you can buy Nitric I believe.

I'll look into that. I used to have one, but not currently.

Muslin is what most use as anode bag.

Will find some!

A higher concentration Silver Nitrate is preferred I believe.

I have some powdered on order. I can up the concentration.

Do you have a sketch of your cell?

I hope these make sense

I can't quite wrap my head around the setup when looking at the graphite rod?

The graphite rod was just touching the silver anode as a lead (actually, I wrapped that little bit of silver at the tip around the graphite rod.) It was just so I could have the whole silver blob in the electrolyte, without the alligator clip going into the solution.

Are you using proper Stainless steel?

Don't know. According to amazon, yes. But maybe it's crap?

Low quality or ordinary steel, might dissolve and introduce Iron into the system.

Im wondering if that's the issue

In fact, I think it HAS to be. Everything else between the jar cell and the SS bowl cell are pretty much identical. The cathod is the only difference.

Maybe you can answer my other question. Is there any reason not to use silver as both anode and cathode? I don't need it to be crystals. If I just put a plate of fine silver and let it collect on that (so I can melt it down for casting) ... would that work?

 

[Yggdrasil]

I'll look into that. I used to have one, but not currently.

Will find some!

I have some powdered on order. I can up the concentration.


I hope these make sense
View attachment 64753
View attachment 64754

The graphite rod was just touching the silver anode as a lead (actually, I wrapped that little bit of silver at the tip around the graphite rod.) It was just so I could have the whole silver blob in the electrolyte, without the alligator clip going into the solution.

Don't know. According to amazon, yes. But maybe it's crap?

Im wondering if that's the issue

In fact, I think it HAS to be. Everything else between the jar cell and the SS bowl cell are pretty much identical. The cathod is the only difference.

Maybe you can answer my other question. Is there any reason not to use silver as both anode and cathode? I don't need it to be crystals. If I just put a plate of fine silver and let it collect on that (so I can melt it down for casting) ... would that work?

No need to use Silver as Cathode, SS is fine.
I think the problem with the original cell is the anode bag and maybe the material in the alligator clips.
Most have a cast Silver anode with a piece of Silver sticking up or something that don't get into the electrolyte.
Alligator clips NEED to be kept dry and out of the electrolyte.

 

[rightmirem]

No need to use Silver as Cathode, SS is fine.
I think the problem with the original cell is the anode bag and maybe the material in the alligator clips.
Most have a cast Silver anode with a piece of Silver sticking up or something that don't get into the electrolyte.
Alligator clips NEED to be kept dry and out of the electrolyte.

The alligator clips never touched the electrolyte. They were attached, as you said either, through a silver or graphite connector. I tried to show that in the pics, but I'm not great at that What material should the allocator clips be made of. I think, right now, their either steel or aluminum (they came with the lab power supply.)

Will the parts of the silver not in the electrolyte not be oxidized?

As for plating directly to silver, part of the reason I ask is plating to the bowl is (for my purposes) an extra step anyway. It would work better if I plated directly to a silver core that I would then just rinse and melt down, versus plating to the bowl which I have to scrape and wash and then melt down

 

[Master Nater]

i have found the easiest way to attach a cathode, is to just coil some bare copper wire under the stainless bowl, and set it on top. no chance of dipping into the solution, or un-sealing the top lip of the bowl. Good luck!

 

[Marcel]

i have found the easiest way to attach a cathode, is to just coil some bare copper wire under the stainless bowl, and set it on top. no chance of dipping into the solution, or un-sealing the top lip of the bowl. Good luck!

Wow! How could I have missed that? Genius idea.

 

[rightmirem]

Just an update...

The slime was definitely silver slime. I dried it out and threw it in my crucible. It's not good quality silver for sure. Treating it with silver acid solution shows a of contaminants (solution turned red.) I know there's a lot fo copper in it.

But it's probably good enough to go through another round of electrolysis?



View attachment silver from slime-1.mp4