Skimming base metals

[nickvc]

Goran I can see the logic of what you are saying about the additional copper as I ran loads of sterling scrap through a silver cell, kilos and kilos, and avoided the fouling with added increments of nitric to dissolve more silver back into the electrolyte, it eventually had to be changed and I did it all by judgement and luck.
I think I'm going back to the trials I know Harold did and I tried which was to run gold filled through a copper cell, that was a total failure for both of us, it worked somewhat better using an old flower poor as a membrane but I gave up after a while...
The OP could try my technique and add small additions of sulphuric after each day's running of the cell, if I remember correctly the cell should still produce fine metal so long as there is enough copper present in the electolyte, well it did with the sterling.
Perhaps you can comment on whether this might be a viable idea as the physics and chemistry theories are beyond me

 

[g_axelsson]

nickvc, that's the way I would run a cell and close to what a larger refinery is doing, they constantly tap some of the copper sulfate from the cell while they add fresh copper sulfate to the solution so they could run the process under tight control. Removing some of the electrolyte while topping up on sulfuric should also work. It might not produce the cleanest copper but that is not what we are after.

In a commercial copper refiner the main contamination seems to be nickel and that is extracted as nickel sulfate after the copper is removed by electrowinning from the used electrolyte.

I'm sure there are a lot of other pitfalls that I'm not aware of, especially if you are running a smaller cell.

This is a project that I'm dying to test some day, I already got a suitable power supply, programmable +/- 10V at 100A. 8)

Göran

 

[nickvc]

Goran I think that experiment could prove to be very very interesting, especially as most members are running e scrap which has a large copper content in many cases.
If someone could find a way to run e scrap an a small scale using cells to do the recoveries I think that it would become the number one choice for many, less fumes and as sulphuric is used ease of getting the acid would make it highly appealing and with the potential that the copper produced could be sold on even if slightly contaminated, as we both know fouling of the electrolyte is the major problem and whether just by trial and error or experience we could work out the parameters of running the cell long enough to reduce 10 kilos of mixed metals to say 250 grams of slimes in one solution with just small additions of sulphuric would I feel be a Great Leap Forward.
I'm sure that certain metals will remain troublesome, even the big copper refineries have penalties for certain metals, but you could run any impure copper produced alongside your next scrap bar to increase the amount of copper going in the electrolyte against the amount of troublesome metals, not sure it would work but could be worth a trial.

 

[madelyn]

Ok, so if I understand this correctly, I can run the bar as it is without adding copper to increase the purity, and just add small increments of nitric to keep on dissolving copper into the cell?
Wouldn't adding a clean copper bar next to the mixed bar also help with this?
Also,what happens when the solution gets contaminated with the other metals?

 

[nickvc]

I think you mean sulphuric not nitric as copper refining is done using copper sulphate.
When I was running my silver cells I could tell by the colour of the solution when it needed more nitric to dissolve more silver into the electrolyte, I have never run a copper cell so you would have to run it on a trial and error basis, when you make up your electolyte note the colour and as the cell runs if the colour starts to change then add more sulphuric to consume more copper, I think that so long as you maintain the copper concentration you shouldn't have too much trouble with other metals plating out but do some research and check that that is true, you will also have to remove some of the acid as you add more at some stage.
As to adding a copper bar I think that might work but the downside is it will take longer to do, I'm not an expert on copper refining but as I said it's an old technology and there are loads of artcles available to read and learn from.
My suggestion would be to start small maybe do a kilo to start with to see how or if it works and how well, do some homework and try it and keep us informed as to your progress and good luck.

 

[madelyn]

I finally finished smelting more than half of the 80kg cell scrap today and produced 2 large bars almost weighing 10kg.
I took a small sample from the melt and tested it with the cell and ran a 30gram just by plating it without the addition of copper sulphate.
I than took the copper sponge produced and dissolved it with nitric to test for values.
The slimes tested positive with gold.

My conclusion was, why not plate the bar directly like this , seeing that the copper produced is very clean with little contamination and than melt the sponge again and plate it out for the second time?
The first cell would leave most contamination in the slime and the second run should produce a very clean bar?

 

[4metals]

The one thing an electroplating cell needs is good electrical contact. That piece you have posted would perform horribly as an anode and wouldn't maintain enough electrical contact properly. The anode needs to have good electrical contact throughout the anode which requires it to be all metal, yours appears to be hmmmm.... well not all metal! It isn't even a bar.

 

[madelyn]

I totally agree with you 4metals, but this is only one half. If you look close you will see there is a hole on top where the flux is still present. This is where I tried to place a thin copper tubing when it was casted and stil hot, unfortunately for this one it was freezed already, but on the other half it worked very good.
I will simply clean this one of and solder a wire to the bar for contact on the top.