dissolve copper ingots

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A

alvaschein

Active member
Joined
Feb 13, 2013
Messages
37
Location
Switzerland
Hi all

I guess I had a very weak moment when I bought 4 copper ingots of about 2 1/2 ozs each (composed of melted gold plated pins). Now I'm trying to get to the supposed gold in them.
I tried following methods:
- cell for electrolytical copper refining: As most know, to get copper of high purity they use this method for refinig raw-copper. The remaining sludge (should) contains PM's. I tryied it too and found it not very suitable for my needs. I didn't get really a good cuality of Cu on the cathode. It looked more like Santa's beard. There were also a lot of particles everywhere, so I couldn't really distinguish it from the anode's sludge. After two weeks I stopped the process. One thing I observed was that I wasn't able to get the necessary high current for this process (0.4 V @ lots of amperes). I treated the sludge with AR and tested positive for Au. The solution seems to have few impurities (yellow with a very slight green touch).
- diluted piranha acid: Please don't scold me for this. I know it's a crazy thing but I wanted to dissolve it as fast as possible. Well, here too I quit the game after one week. I got some sludge which I filtered and treated with AR. The stannous chloride test was positive but the solution still contains a lot of Cu.
- last (for me) but not least I put the remaining ounce in AP. Now I'm waiting what will happen the next days.

Does anybody kow an other method? Or has anyone experience with a copper refining cell? I still have 3 ingots and want to tickle them the gold out.

Thanks

Roy
 
piranha is too expensive for large amounts

AP is slow

iron III chloride is faster, but too expensive

When using AR on the slimes, you have first to dissolve all base metals.

Copper cell would be my choice, but it is an art of it's own. There is a very good artikle about it on the forum, I will try to find for you.
 
The problem with "gold drops" sold on ebay is that you can never be sure of the metal composition. And if you scan with an XRF you are only going to get a reading on whatever metals are closest to the outside of the metal drop/bar whatever you want to call it.

Unfortunately, you not only cannot be sure what metals are alloyed, but you cannot be sure if the melt was homogenous or if they just melted and poured as soon as they were able.

So the first step in your process would probably be to melt your gold drop so that is a homogenous melt, then to pour it correctly into more a thin anode, than thick. This is done so that the metals are alloyed correctly and your anode has more surface area, and can then be parted in a cell properly.

I am assuming you were using an electrolyte of CuSO4. If you run too high a voltage, you will end up depositing other metals onto the cathode, also as more impurities build up in your electrolyte, the more resistance there is, so a cleaner rather than dirty solution is better. I believe the correct Voltage is between .15-.30.

Because Ag, Au, Pd and Pt are more "noble" or less reactive, they will not dissolve, and will create part of the anode slime.

Sn, Bi and Sb will dissolve, but will precipitate in the electrolyte as oxides or hydroxides, which also will be found in the anode slime.

Pb is oxidized but will form insoluble lead sulphate, and will end up in your anode slime as well.

Fe, Ni, Co and Zn all dissolve, and are soluble in the electrolyte, but only reduce at potentials negative to that at which copper deposits so should remain in the electrolyte solution!

So your anode slime may have Ag, Au, Pd, Pt, Sn, Bi, Sb and Pb, with Fe, Ni, Co and Zn possible in the electrolyte solution.

I'm just going on notes I have written down when I was operating a copper cell. I would have to refer to my books to post anything further. What specifically did you want to know? Maybe someone can help you further, or if not, if I know the question I might be able to help you further.

Scott
 
@solar_plasma, @scott

Thank you very much for your fast reply!

My first choice would be the copper cell and I would like to build one. But... I first stumbled on the current requirements. In literature they write of a current density of 110A per square feet at 0.25-0.4 V.

I built a cell of the dimensions h x w x d of 3"x3"x3". The electrolyte was with H2SO4 acidified CuSO4. The cathode was a cuppersheet 2.5" by 1" and the anode an ingot of 0.25"x0.75"x1.75" (more or less). I measured the resistance between anode and cathode and found about 240 ohms. So calculating with the Ohm's law for DC, there would be a max. current flowing at 0.4 V of 1.6 mA. Gosh, that's nothing... or am I wrong? So, if I continue with my calculation, that would give a current density of 0,6 mA per square inch. That's really nothing! This was the reason why I increased the tension to 2.4 V (stupid me!) which had effect! Everything began to grow (Santa's beard) and mud everywhere in the solution. And that was the mistake, I guess.
That's what I did.
Now my question. How must the power supply be dimensioned to get a halfway high current density. I have different ones, e.g. for 12V/2.5A. So If I reduce the voltage through a voltage divider, 96% of energy would be lost as heat. So, has anyone a hint how I could solve the power problem?

Thanks in advance

Roy
 
solar_plasma said:
Here is the link I mentioned. Of course this will only work well with really high copper content.

Chapter 16:

http://uctm.edu/departments/MCMT/BG/E-library/Extractive_Metallurgy_of_Copper_-_G._W._DAVENPORT.pdf
Click to expand...

Thank you for the link. I know this document but maybe I was too impatient in studying.

solar_plasma said:
edit: my belief is, those ingots are not worth processing.
Click to expand...
I guess you're right, those ingots are not woth processing. Especially as Scott wrote, you don't know what's inside. When I have a hand full of gold plated pins, first I know what I have, second I know how to process them and third I would't melt them down.
OK, one more mark on my list of apprenticeship.

Roy
 
alvaschein said:
I built a cell of the dimensions h x w x d of 3"x3"x3". The electrolyte was with H2SO4 acidified CuSO4. The cathode was a copper sheet 2.5" by 1" and the anode an ingot of 0.25"x0.75"x1.75" (more or less). I measured the resistance between anode and cathode and found about 240 ohms. So calculating with the Ohm's law for DC, there would be a max. current flowing at 0.4 V of 1.6 mA. Gosh, that's nothing... or am I wrong? So, if I continue with my calculation, that would give a current density of 0,6 mA per square inch. That's really nothing! This was the reason why I increased the tension to 2.4 V (stupid me!) which had effect! Everything began to grow (Santa's beard) and mud everywhere in the solution. And that was the mistake, I guess.
That's what I did.
Now my question. How must the power supply be dimensioned to get a halfway high current density. I have different ones, e.g. for 12V/2.5A. So If I reduce the voltage through a voltage divider, 96% of energy would be lost as heat. So, has anyone a hint how I could solve the power problem?

Thanks in advance

Roy
Click to expand...
To increase the current density decrease the distance between anode and cathode and use the same area on anode and cathode. The area to use for the calculation is the area facing the other electrode.

Did you measure the voltage and current when running the cell or did you only measure the resistance with a multimeter? You can't use a multimeter to measure the resistance in a cell, if the electrodes are of different metal alloys you will get a battery effect with polarity and the resistance will be non linear. The minute voltage used by a multimeter will have a hard time overcoming polarity issues in the cell. The correct way to measure cell resistance is to measure the voltage between the electrodes and the current running through the cell and then calculate the resistance.

A couple of years ago (20+) I made a couple of blobs myself in a failed attempt to refine via a copper cell. This summer when I found them I thought about it a little while, then I put them in my stock pot and they are dissolving fine. The gold ends up with the sediments in the stock pot and in time I'll get my gold. I wouldn't spend any time trying to refine a couple of blobs.

Göran
 
I'd shoot for the stock pot as well. Melt them if possible and pour into a bucket of H2O. That would make alot of surface area for acids to work through the metals...

B.S.
... If you don't try and just not bother, You will never remember what you learn...
 
I'd shoot for the stock pot as well. Melt them if possible and pour into a bucket of H2O. That would make alot of surface area for acids to work through the metals...

B.S.
... If you don't try and just not bother, You will never remember what you learn...
 
@all

Thanks a lot for your advices. They are very valuable for me.

I think I'll do like Göran and Pantherlikher - remelt and put them in the stock pot.

So I won't have to bother with dimensioning a copper cell.


Have a nice day, evening, night - wherever you are.

Roy
 

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