Cathode grade copper

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SapunovDmitry

Well-known member
Joined
Dec 7, 2007
Messages
332
Location
Moscow
Guys, i want to try to make a sheet of cathode grade copper at home.
Can anyone give advices about process?
I am going to use sulfuric cell for this.
Maybe someone of you worked for electrolytic copper refineres?
What do they do to make clean shiny pink copper plates?
 
Unless it's a burning desire, you're far better served to simply use copper wire. It is, of necessity, made from cathode copper.

A simple sulfuric cell is all that is required, but you must start with relatively pure copper at the outset. Contamination of the electrolyte leads to rapid degradation of the deposited copper, yielding copper sponge that falls off the cathode instead of adhering tightly.

Common design is one whereby anode and cathodes are alternated on a rack system. Stainless sheet can function as the cathode, or a sheet of pure copper can be used instead. Some refineries use a titanium starter sheet, from which the copper is pulled when the deposit is thick enough.

A filter bag is generally placed over the anodes, where insoluble contaminants are collected (the anode "slimes", where the precious metals included in the copper are to be found after parting).

Sorry, I don't have any technical information regarding voltage and acid concentration, but you should be able to find that information by searching for a copper parting cell online.

A side note. Coppper is not soluble in dilute sulfuric acid, but copper oxides are. You can achieve the nice copper color you described simply by using dilute sulfuric to clean the surface of copper. The problem is it won't stay that way for very long.

Cyanide is also used to create a bright surface, but that is likely not a viable choice for you.

Harold
 
Yep. It's just because i want to try and make it, i can't find better words than "burning desire" :) .It's 10 out of 10 shot. I want to make it and then put it on the shelf above my bed.
I use 0,4 V voltage and the current is 0,07 A now and rising very fast (0,01 A per 15 minutes). I use about 70 % sufluric/dist. water.
I started it an hour ago. Now my solution is light blue because of the dissolved copper. I use two sheets of copper. One for cathode, the other one as the anode.
Using such low voltage is recommended for good copper deposition.
But there is some sludge already below the anode.
I tnink i will be running my cell for 14 days non-stop and cleaning my electrolyte every 12 hours.
I use areometer to determine CuSO4 concentration in electrolyte.
 
If you do not mind me asking, what is the surface area of your anode and cathode to the acid and what spacing are you using between them?
 
Current density now is 125 A/m2. Copper sheets are flat and are 1 cm high and 7,5 cm wide (the part that is submerged in the electrolyte).
I am just curious how long will it take to make 1 sheet out of two)))
 
I haven't worked in a copper refinery, but I once spent a week in the Anaconda tankhouse, which, if I remember right, had 400, 600 gallon tanks. I have deposited copper from this solution quite a few times.

If you want to do this right, you should start with a solution already made up in the following manner. I haven't worked with it in a long time and didn't remember the exact operating conditions. However, there is a ton of information on the internet. In general, here's a typical solution formulation and operating conditions.

CuSO4.5H2O = 100-160 g/l
H2SO4 = 180-250 g/l (I calculate this as about 10-14% conc. H2SO4, by volume)
[Cl-] (added as HCl) = .02-.05 g/l
Thiourea = .0001-.0005 g/l
Bone glue = .0001-.0010 g/l
Temp. = 55-65 C
Cathode Current Density = 130-170 A/m2

If I remember right, the bone glue is dissolved in hot water before adding. The thiourea and glue act as grain refiners and are basically what will produce the smooth finish you're after. They also prevent treeing of the deposit. Their consumption is proportional to the number of amp-hours used and can be controlled by keeping track of the bath usage. You can probably get away without these additives, but the deposit will not be nearly as smooth and could be stressed. I have also used iron-free blackstrap molasses or dissolved gelatin as a grain refiner

At 100% efficiency, copper deposits at the rate of 1.185 gram/A-hr. The efficiency of this bath is about 92-96%.

What immediately caught my eye is that you're using 70% H2SO4, by volume. That's 5-7 times stronger than what you should be using. I can see many problems with using the strong acid. Both the cathode and anode efficiencies will be quite low. The solubility of the copper will be very low. The deposit will probably look terrible, if it deposits at all. Think of the sulfuric gold stripper. According to the patent, I think it can be run as low as 65% H2SO4, yet it neither dissolves or deposits copper, to any great extent.

In acid copper plating, which uses a very similar formula, air agitation is used. This further improves the deposit and makes it more uniform. It is supplied from a blower and not a compressor, since oils can be very detrimental. I don't know if air agitation is used in a copper refinery, or not. Also, constant filtration is used in a plating tank.

Like Harold said, bag the anodes to prevent undissolved impurities from fouling the solution and the deposit. A polyester bag sewn with polyester thread works well.

I would imagine that the anode area should be at least as large as the cathode area. In plating, it's usually 2/1, anode/cathode.
 
Ok. I am with my first pics of this horrible thing.
It deposits, but it is awful. The left one is cathode, and the right one is anode.
Picture was made after 24 hours of processing.
Now i have canceled everything and started again using dilute sulfuric acid as GSP said.
I don't use glue, because i was unable to find it in such a short period and i cannot add exact quantity in my little experiment. So i decided to use low voltage to make less bubbles and not to spoil the surface of the cathode. In fact there are no bubbles at all, but current is 0,07 A now, so it runs ( i hope so...). :D
 
I thought NOXX had experiance with refining copper in an electrolytic cell?

Im very interested in this also

kev
 
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