Gold-Filled jewelry in sulfuric acid stripping cell viable?

[OneCrunkMonk]

Quick question, I know that gold-filled jewelry is a heavy sheet of karat gold (10k and12k usually, with 14k and 18k on high-end jewelry) mechanically attached to a base metal component. From my point of view, the biggest issue with economically recovering gold from gold-filled is the sheer amount of base metals relative to values. In my case, I have gold-filled watch bands, that have 10 and 12 karat gold mechanically attached to 316 stainless steel. I can think of two ways to chemically remove the gold from the stainless steel without using nitric acid( really expensive). 1. Sulfuric acid stripping cell. 2. Electrolytic dissolution of the stainless steel. (US2865832A - Electrolytic dissolution of stainless steel - Google Patents). I would prefer to use the 1st option as it would use less acid and therefore be more cost-efficient. Would a sulfuric acid strip cell work for this application?

My material type. ( not my material but similar.)

 

[OneCrunkMonk]

Quick clairfication. The electrolytic dissolution of the stainless steel process I linked uses nitric. I forgot to clarify that I would be using HCl or sulfuric. Also, I am fully aware that sulfuric acid is more hazardous than HCL.

 

[richoc]

I process gold filled in a sulfuric cell all the time.
Control is the word here, you must really be on your game.
You must control your acid temperature in your cell and keep the moisture out of the sulfuric acid.
I warn you that this is not a first timer way to go.
You must set up a safe system, safe lab area and have all PPE as hot sulfric acid is very dangerious and the off gassing is flamable.

 

[OneCrunkMonk]

Yes, thank you. I am aware of just how dangerous the sulfuric acid cells are. The cell needs to be cooled and or turned off when it starts to increase in temperature. Also, water can send hot sulfuric acid everywhere as you indirectly mentioned. After further research, I found that 316 stainless steel should dissolve in 20 plus percent ( I have access to 33 percent HCL, FYI) HCL when heated. I think that would be a better option. I was under the impression that the stainless wouldn't dissolve fast enough based on earlier research. Thanks.

 

[Yggdrasil]

Yes, thank you. I am aware of just how dangerous the sulfuric acid cells are. The cell needs to be cooled and or turned off when it starts to increase in temperature. Also, water can send hot sulfuric acid everywhere as you indirectly mentioned. After further research, I found that 316 stainless steel should dissolve in 20 plus percent ( I have access to 33 percent HCL, FYI) HCL when heated. I think that would be a better option. I was under the impression that the stainless wouldn't dissolve fast enough based on earlier research. Thanks.

Tha main issue with the sulfuric cell and water, is not splattering, but sulfuric is hydrophilic and will soak up water from the atmosphere until it is diluted enough to dissolve the copper basket.

If course the caution regarding acid and water goes as always with any concentrated acid.

 

[nickvc]

You can mechanically strip the gold filled pieces using decent cutters and or pliers , using hot HCl will dissolve the stainless but you will use a lot of acid to do so which adds to your waste stream that will need treating before disposal so the time saved not mechanically stripping is used treating waste.

 

[OneCrunkMonk]

Already done.

 

[richoc]

A benefit to striping cells is you need not use extra resources to reduce all metals, you clean and rinse them for sale to a scrap yard.
If gold over stainless you remove only the gold alloy, run a wash system as gold/black sludge will hang on parts, rinse and neutralize.
You have stainless parts left over that still have a value you can sell.
You do not waste any acid as you decant it and reuse the acid over and over controlling the water content as needed.
Your only harvesting the Gold alloy for recovery and refinement.
I store the sludge from many cell runs until I have enough to proceed with processing it to recover the Gold.
Supplies to build a cell are very easy to come by, high grade sulfuric acid is readily purchased even at Walmart.

One system I am currently looking to try is a Salt water cell.
Salt water is the electrolyte replacing the sulfuric acid.
The one issue I see in this method is the high amperage of the system at 12 volts at 15 and higher amps.

Currently I try to keep my cells running 3 amps at 12 volts to keep the excess heating down.
So my power supply's are geared to fine control of lesser amounts of power, I do not think any of them will put out 8 amps max.

 

[OneCrunkMonk]

That's a very interesting possibility, I will look into that. Thank you to everyone.

 

[Joip11421]

I process gold filled in a sulfuric cell all the time.
Control is the word here, you must really be on your game.
You must control your acid temperature in your cell and keep the moisture out of the sulfuric acid.
I warn you that this is not a first timer way to go.
You must set up a safe system, safe lab area and have all PPE as hot sulfric acid is very dangerious and the off gassing is flamable.

I live in a very desert environment, setting up my "LAB" in a metal shed I just acquired, going to set up in a corner of my backyard (rock covered - nothing grows here). I've watch numerous videos on this subject and the biggest question is, how can I use this process in my environment?

 

[Alondro]

I process gold filled in a sulfuric cell all the time.
Control is the word here, you must really be on your game.
You must control your acid temperature in your cell and keep the moisture out of the sulfuric acid.
I warn you that this is not a first timer way to go.
You must set up a safe system, safe lab area and have all PPE as hot sulfric acid is very dangerious and the off gassing is flamable.

It's best to have proper lab glassware for sulfuric acid cells, like the setup Sreetips has. You want to have good glass fittings, an addition funnel, and a bubbler into 20% hydrogen peroxide to catch the waste SO2 gas (it will convert back to sulfuric acid with near-complete efficiency in H2O2).

I have most of the glassware I need, but I need the space to do it. Garage is STILL full of a dismantled Triumph GT6 my dad took apart 35 years ago.

 

[Geo]

I'm not sure that you are not stripping gold plating. In my experience, gold filled gold is too thick to be affected by the electrolyte. The chemical mechanism that causes the actual stripping is a very small amount of persulfuric acid formed on the surface of the anode. The gold is dissolved by this tiny amount of persulfuric acid. As it is pulled away from the vicinity of the anode, this particular species of persulfuric is not a stable form and and decomposes about as soon as it's created, the persulfuric acid decomposes and drops the metallic gold as a fine black dust. The amount of persulfuric is so minute that it can only dissolve very thin gold plating 30µi or less in thickness. I have tried gold filled before and it sat in the cell with no effect on the gold. It began attacking base metal without attacking the gold.

 

[Geo]

I have never experienced SO2 or SO3 while running a stripping cell. It does emit oxygen and hydrogen so be very careful not to connect or disconnect the power supply from either anode or cathode without first turning off the electricity to the power supply first. The bubbles that form are a mixture of oxygen and hydrogen. A small bubble of gas can explode like a firecracker and fling concentrated sulfuric acid in all directions.

 

[Geo]

I leach watch bands whole in nitric acid. It will not dissolve the stainless steel but with an addition of sulfuric acid (about 5ml's per 100ml's of solution) , it will dissolve the springs and base metal (besides the SS) leaving the stainless steel and gold behind. The caps from the watch bands is normally gold over silver. So you can recover the silver with cementation on copper.

 

[Martijn]

I'm not sure that you are not stripping gold plating. In my experience, gold filled gold is too thick to be affected by the electrolyte. The chemical mechanism that causes the actual stripping is a very small amount of persulfuric acid formed on the surface of the anode. The gold is dissolved by this tiny amount of persulfuric acid. As it is pulled away from the vicinity of the anode, this particular species of persulfuric is not a stable form and and decomposes about as soon as it's created, the persulfuric acid decomposes and drops the metallic gold as a fine black dust. The amount of persulfuric is so minute that it can only dissolve very thin gold plating 30µi or less in thickness. I have tried gold filled before and it sat in the cell with no effect on the gold. It began attacking base metal without attacking the gold.

Geo, is that the same species of peroxymonosulfuric acid, labeled as highly explosive on wikipedia?
Do you know if there is a real danger of detonation while stripping gold plating? That would be a big safety concern to try and control, if even possible / neccessary.

I was also curious and was considering to test how gold filled or even carat gold reacts in the cell. You had your doubts that Ricoh actually was stripping gold plated.
Worth trying at least imo. If it wont blow up in my face. Big if.
I hope I was not just lucky stripping my plated material.
I limit the current to 2 amps, that should keep sparks small and electrolyte temperature low.
Edited for spelling.

 

[Yggdrasil]

Geo, is that the same species of peroxymonosulfuric acid, labeled as highly explosive on wikipedia?
Do you know if there is a real danger of detonation while stripping gold plating? That would be a big safety concern to try and control, if even possible / neccessary.

I was also curious and was considering to test how gold filled or even carat gold reacts in the cell. You had your doubts that Ricoh actually was stripping gold plated.
Worth trying at least imo. If it wont blow up in my face. Big if.
I hope I was not just lucky stripping my plated material.
I limit the current to 2 amps, that should keep sparks small and electrolyte temperature low.
Edited for spelling.

I think what you are talking about is Oxone and not PerSulfuric acid which is created close to the "Anode?" briefly when running the cell.
It goes back to Sulfuric just a short distance away, so it might just be some kind of short lived ionic compound of it.

Edit to add:
I just checked and it seems it is not Oxone, that is different animal all together.

 

[Martijn]

Thinking back, i once played with silver contacts in the cell with fresh acid and sparks were coming off at 25 volts... so i guess it must be safe to operate it at 6 volts and 2 amp.

 

[Geo]

Geo, is that the same species of peroxymonosulfuric acid, labeled as highly explosive on wikipedia?
Do you know if there is a real danger of detonation while stripping gold plating? That would be a big safety concern to try and control, if even possible / neccessary.

I was also curious and was considering to test how gold filled or even carat gold reacts in the cell. You had your doubts that Ricoh actually was stripping gold plated.
Worth trying at least imo. If it wont blow up in my face. Big if.
I hope I was not just lucky stripping my plated material.
I limit the current to 2 amps, that should keep sparks small and electrolyte temperature low.
Edited for spelling.

The explosive gas that can detonate is hydrogen and oxygen. In all the chemistry we do, there is two constants that can't be changed, we are either add or removing oxygen and/or hydrogen. In an electrolytic cell, hydrogen is expelled at the anode and oxygen is expelled at the cathode. The spark hazard exist any time a connection is made between the anode and cathode. For this reason, the cell should be powered off while loading or unloading and connecting or disconnecting the power supply. The real danger is the bubbles generated at the anode. As the persulfuric acid is being generated, the left over hydrogen is pushed out of solution and creates these bubbles. Persulfuric acid is just sulfuric acid with an oxygen atom attached. The oxygen comes from a water molecule in the sulfuric acid. It steals the O2 and expels the H. Any spark, even a static spark can detonate these small bubbles of gas. They can be considered powerful for their size. The presence of bubbles poses an explosion hazard at any time due to static spark hazard.

 

[Martijn]

I leach watch bands whole in nitric acid. It will not dissolve the stainless steel but with an addition of sulfuric acid (about 5ml's per 100ml's of solution) , it will dissolve the springs and base metal (besides the SS) leaving the stainless steel and gold behind. The caps from the watch bands is normally gold over silver. So you can recover the silver with cementation on copper.

Thanks for that tip! Just tried it small scale without the sulfuric and it works great and fast too!
Do you ever experienced pieces popping apart when the springs dissolve?

 

[Geo]

Thanks for that tip! Just tried it small scale without the sulfuric and it works great and fast too!
Do you ever experienced pieces popping apart when the springs dissolve?

No. The gold will be heavy flakes and will get stuck between the springy caps. It takes time to pull them apart to get all the gold out. Without the springs, you can rinse the gold out with a spray bottle.