Copper refining

[Bluebloomer]

Hi all,

I have a solution of acidified copper sulphate, a lab powersupply (2,5A) a sheet of pure and clean copper as the kathode, and a piece of copper pipe from my stockpot that has been cemented with all kinds of metal, as the anode.

From what I have read, this is a basic copper refining cell but it does not seem to work.

With the H2O cell you see the liquid travel from one side to the other, but in the copper cell I only see minor bubbling from the kathode, but the impurites stay on the annode.

So, what am I doing wrong, or does this process take way longer as anticipated?
All alligator clips are connected properly, and I have added a bit of salt to make it more conductive.

 

[g_axelsson]

and I have added a bit of salt to make it more conductive.

What type of salt? NaCl? You don't want to have chloride ions in a copper cell as it will release chlorine gas.

What is the voltage? pH? Current density?

You need to control the properties of the cell to get a copper cell that is working well. It isn't just to connect some cables and hit it with all you got, that will give you a random result, it might work but you might as well get strange result and bad quality of copper.

Göran

 

[solar_plasma]

Just read some papers about how the big copper refineries do! Then you get a feeling for how complicated and complex this topic is. Concentration, additives, voltage, electrode distance, temperature, fog control, bypassing electrolyte before fouling and introduction of fresh (probably recycled) electrolyte and the right level of agitation.

With a small hobby set up it will run and then again not, very instable. You have to intervene all the time. And yes, it is very very slow. Count days.

At the end you feel you understand most of it, when you'll get copper moss or when you get some really resistable deposit on the cathode, when to change electrolyte and when to modify voltage. But considering time, work and waste, this is a mess compared to the tiny value.

 

[FrugalRefiner]

I've never heard of anyone approaching a copper cell this way. Everything I've read starts with an anode that is melted and poured into the anode mold. All the metals are mixed together in the anode. As the copper cell runs, the anode dissolves, the copper is transported through the electrolyte, and it deposits at the cathode. Some of the impurities dissolve into the electrolyte, and must be kept under control to keep them from depositing along with the copper. Other impurities do not dissolve and end up as the "slimes". That's where any gold is usually recovered.

But it sounds like you're starting with a piece of copper coated with other metals, not a mixture. It's almost like you're trying to dissolve away the base metal (copper) from a "plated" material. While you may succeed in having the coating separate from the copper, it's not really how a copper cell is designed to work.

Why not physically remove the coating from the copper and refine from there? You could scrape, grind, sand, or use some similar process. Another idea would be to put the coated piece of copper in some AP solution, where the copper would eventually dissolve, but here again you'd be dissolving all the copper just to end up with the stuff that's coating it.

If I'm misunderstanding what you're doing or what you're trying to accomplish, just let me know.

Dave

 

[goldsilverpro]

and I have added a bit of salt to make it more conductive.

What type of salt? NaCl? You don't want to have chloride ions in a copper cell as it will release chlorine gas.

Not necessarily true. A small amount of Cl- is necessary for proper corrosion of the anodes. Otherwise, the anodes can polarize. Every modern formula for copper sulfate plating baths or electrorefining baths requires 50-120ppm Cl- . This should be added as HCl - this is a tiny amount. I used to add it by counting the drops of HCl from an eyedropper - I usually tested an eyedropper or two to determine the # of drops in 1ml - it can vary between 15 and 25 drops per ml. In my experience, the Cl- at that low level is quite stable and doesn't tend to decompose at the anode. It is important, however, not to exceed the 120ppm.

 

[goldsilverpro]

I've never heard of anyone approaching a copper cell this way. Everything I've read starts with an anode that is melted and poured into the anode mold. All the metals are mixed together in the anode. As the copper cell runs, the anode dissolves, the copper is transported through the electrolyte, and it deposits at the cathode. Some of the impurities dissolve into the electrolyte, and must be kept under control to keep them from depositing along with the copper. Other impurities do not dissolve and end up as the "slimes". That's where any gold is usually recovered.

But it sounds like you're starting with a piece of copper coated with other metals, not a mixture. It's almost like you're trying to dissolve away the base metal (copper) from a "plated" material. While you may succeed in having the coating separate from the copper, it's not really how a copper cell is designed to work.

Why not physically remove the coating from the copper and refine from there? You could scrape, grind, sand, or use some similar process. Another idea would be to put the coated piece of copper in some AP solution, where the copper would eventually dissolve, but here again you'd be dissolving all the copper just to end up with the stuff that's coating it.

If I'm misunderstanding what you're doing or what you're trying to accomplish, just let me know.

Dave

My thoughts exactly.

 

[g_axelsson]

and I have added a bit of salt to make it more conductive.

What type of salt? NaCl? You don't want to have chloride ions in a copper cell as it will release chlorine gas.

Not necessarily true. A small amount of Cl- is necessary for proper corrosion of the anodes. Otherwise, the anodes can polarize. Every modern formula for copper sulfate plating baths or electrorefining baths requires 50-120ppm Cl- . This should be added as HCl - this is a tiny amount. I used to add it by counting the drops of HCl from an eyedropper - I usually tested an eyedropper or two to determine the # of drops in 1ml - it can vary between 15 and 25 drops per ml. In my experience, the Cl- at that low level is quite stable and doesn't tend to decompose at the anode. It is important, however, not to exceed the 120ppm.

You are correct, but now we are down to minor details. If you add NaCl to increase conductivity of the electrolyte then you are way over 120 ppm and that will release chlorine.

But we haven't heard back from Bluebloomer yet, he only mentioned salt and that could be a lot, including NaCl or CuSO₄. Salt is such a vague chemical description.

By the way, crocodile clips onto a copper pipe isn't a very good connection and could produce hot spots if the current is high.

Göran

 

[solar_plasma]

CuCl₂ as the electrolyte does not release chlorine gas to the atmosphere. The produced Cl_nasc is directly oxidizing the copper anode. I tried it.

Where comes that idea from of using NaCl? This would make a mess (at least no refined copper), since you will produce NaOH at the cathode. This will precipitate copper hydroxide. I tried it when I was 12 yo and used copper wire directly as electrodes instead of carbon. Different from the experiment with CuCl₂, I remember the NaCl cell produced chlorine gas. Maybe due to the overvoltage I used from a 9V block.