A simple copper electroreduction cell

[Alondro]

I found that using diluted mostly copper chloride waste solution (at least 3 to 1 distilled water to conc metal-HCl mixture resulting from exhausted gold finger or gold pin base metal stripping soln) could be rapidly reduced with a very simple electrochemical setup.

First step is the dilution and allowing sediment which forms to settle out, then put the clear solution into a new vessel for the reduction. Instead of merely using an iron rod, I used a copper rod connected to iron with a copper wire outside the solution. This set up a current flow, which intensified as the solution was used up and the iron rod shrank. The solution stratified to layers of different ionic strength and this increased the current to the point where copper crystals began to grow on the copper electrode as well as on the iron. I've made this setup 5 times now. It's quite fascinating, and cleans up the copper from the solution very rapidly, usually in about 4 days. You get some very beautiful frost-like copper crystals of exceedingly high purity.

Here are two pics: what it looks like to start, and then after the electroreduction process is complete.

 

[stella polaris]

Simple is best! You got a like for that.

 

[Martijn]

Thats is very inventive. You're using the galvanic effect to electrowin and cement at the same time.
The voltage and current increase as more salts are reduced and the acid is released back into solution making the solution more acidic. Making the galvanic effect stronger and increasing conductivity.

Question: is there any chlorine gas smell released from this setup?

Hat's off!! Good find!

 

[Alondro]

Thats is very inventive. You're using the galvanic effect to electrowin and cement at the same time.
The voltage and current increase as more salts are reduced and the acid is released back into solution making the solution more acidic. Making the galvanic effect stronger and increasing conductivity.

Question: is there any chlorine gas smell released from this setup?

Hat's off!! Good find!

I haven't noticed any chlorine smell at all. Since it's a small volume and the process takes 4 days, it's likely releasing chlorine so slowly that it remains in solution and totally combines with iron before any can bubble out.

 

[Golddigger76]

This is basically working like a battery does right ?
Not connected to a power supply ?

 

[Martijn]

This is basically working like a battery does right ?
Not connected to a power supply ?

Yes

 

[Alondro]

This is basically working like a battery does right ?
Not connected to a power supply ?

Yep, it's a basic acid battery setup, only all the power generated is being used to reduce the copper and dissolve the iron. Using the waste's potential chemical energy to power it's own cleanup!

 

[Golddigger76]

That is exactly what I had pictured, thank you for sharing the idea with us !!!!

 

[Thirmo21]

I found that using diluted mostly copper chloride waste solution (at least 3 to 1 distilled water to conc metal-HCl mixture resulting from exhausted gold finger or gold pin base metal stripping soln) could be rapidly reduced with a very simple electrochemical setup.

First step is the dilution and allowing sediment which forms to settle out, then put the clear solution into a new vessel for the reduction. Instead of merely using an iron rod, I used a copper rod connected to iron with a copper wire outside the solution. This set up a current flow, which intensified as the solution was used up and the iron rod shrank. The solution stratified to layers of different ionic strength and this increased the current to the point where copper crystals began to grow on the copper electrode as well as on the iron. I've made this setup 5 times now. It's quite fascinating, and cleans up the copper from the solution very rapidly, usually in about 4 days. You get some very beautiful frost-like copper crystals of exceedingly high purity.

Here are two pics: what it looks like to start, and then after the electroreduction process is complete.

View attachment 50393

View attachment 50394

This is impressive, i wonder if it could be done with other metals too, to furher purify the acid

 

[Golddigger76]

This is impressive, i wonder if it could be done with other metals too, to furher purify the acid

Iron by itself will cement copper and any other metals below iron it on the reactivity series of metal chart.

 

[Alondro]

Iron by itself will cement copper and any other metals below iron it on the reactivity series of metal chart.View attachment 61763

The galvanic method just makes the reaction work faster, AND it has the advantage of growing much larger crystals, which make pouring off the copper-depleted solution much easier.

Some of the crystals can grow into fascinating shapes on the copper wire too. Got an inch-long 'feather' crystal, quite pretty!

 

[Alondro]

This is impressive, i wonder if it could be done with other metals too, to furher purify the acid

Well, after the copper is depleted, if you have a significant amount of tin and lead in solution, it'll start reducing as a black mossy mass on top of the copper crystals.

 

[offtrailhiker]

I wonder if a silver cell like that can be set up, without an external power source.

 

[Yggdrasil]

I wonder if a silver cell like that can be set up, without an external power source.

No, this is for all practical reasons just a battery.
What powers it, is the potential differential between the different metals in that particular electrolyte. This time HCl.
For a Silver solution it will be Silver Nitrate and Nitric. Silver in one end and Copper in the other.
In the end it is just a cementation on steorides.

 

[Thirmo21]

Well, after the copper is depleted, if you have a significant amount of tin and lead in solution, it'll start reducing as a black mossy mass on top of the copper crystals.

Thx good to know

 

[Alondro]

I wonder if a silver cell like that can be set up, without an external power source.

No, this is for all practical reasons just a battery.
What powers it, is the potential differential between the different metals in that particular electrolyte. This time HCl.
For a Silver solution it will be Silver Nitrate and Nitric. Silver in one end and Copper in the other.
In the end it is just a cementation on steorides.

It's only really useful for copper, because the goal is to clean up the solution. If one is aiming for high-purity silver, this method will not do it.

On the other hand, it might be useful to drop silver from a 'dirty' nitrate solution faster, without having to drop silver chloride or wait for cementation on copper alone to finish. The solution might need to be acidified, and I'd go with a little bit of sulfuric acid (start with a few drops) and let the solution sit until any lead sulfate drops out. Then filter and use a galvanic set up with a silver rod and a copper rod connected by wire. Anything less reactive than the copper should be yanked out of the solution quickly. Since we're talking about nitric acid-based initial solution, it'll be mostly silver and any trace palladium from the scrap metal.

Basically, this could work well as a first step, to get semi-cleaned silver (and palladium) to then melt into shot for proper electrolysis.

It'd be interesting to see what difference in the rate of cementation takes place between identical volumes of silver solution with the two methods: copper rod alone vs the galvanic copper rod-silver rod method.

They should use the same original solution, divided in half into identical glass or plastic beakers. For a properly-controlled scientific setup, the copper cementing reaction must use two copper rods connected with a copper wire, and the galvanic reaction must have a wire-connected copper and silver rod of the same diameter as the copper rods, to ensure there is no difference in surface area, which affected the reaction rate.

Then watch until the reaction is completed, which can be tested by taking a drop of each solution, putting it on a clear glass, and then adding a drop of HCl. When no more white silver chloride forms (or so little that it's barely noticeable) then the reaction can be judged 'complete' and then the time to completion for each setup can be properly compared.

 

[Martijn]

Was there any cementing going on on the iron rod? or did it just dissolve?

 

[Alondro]

Was there any cementing going on on the iron rod? or did it just dissolve?

The copper cemented on the iron, and fell off in stages as the iron dissolved. With a gallon-sized set up I made later, with a small iron plate and larger copper rod, the reduction was so fast I could add more copper-rich solution almost every day (usually poured out about half the spent solution at a time. And using my little greenhouse heater, I could then pour off the spent waste into a small glass fishbowl, put it in front of the heater, and the water all evaporated away leaving a dense rusty brine and salts, reducing the volume by more than 90%.

The initial volume of the concentrated acid waste was about half a gallon, which made 2 gallons of the diluted solution with water. The longest part of the process was waiting for the diluted solution to oxidize and turn from brown-green to blue, and to settle out the grey-white precipitate (mostly tin and antimony oxychlorides, I believe). That took 3 to 4 days. It's a necessary step because the brown-green solution doesn't reduce as well, and dirties the copper with the grey-white goo that forms as it oxidizes.

 

[Thirmo21]

The longest part of the process was waiting for the diluted solution to oxidize and turn from brown-green to blue, and to settle out the grey-white precipitate (mostly tin and antimony oxychlorides, I believe). That took 3 to 4 days. It's a necessary step because the brown-green solution doesn't reduce as well, and dirties the copper with the grey-white goo that forms as it oxidizes.

Great process. Can i ask what do you mean by this part, is oxidization first step before galvanizing?

 

[Alondro]

Great process. Can i ask what do you mean by this part, is oxidization first step before galvanizing?

Yes. You make the diluted waste and let it sit in the open air until it turns blue or blue-green (final color depends on the amount of other dissolved base metal). The color changes from the top down. You can stir it to speed it up.

Then once it's blue, put in the rods for the galvanic process.