electrolytic copper

[Soulkeeper]

I've been reading about the process of purifying copper using copper sulfate solution and have a few questions.

what happens to the zinc/magnesium and other less noble impurities in a copper sulfate electroplating setup when the anode is impure, do they get deposited to the cathode, or do they remain in solution ?

I understand that they will displace the copper in the copper sulfate over time, but will they also plate the cathode along with the copper, creating an alloy ?

thanks

 

[Mark R]

Substances with soluble sulfates will go into solution. The solution will therefore gradually increase in concentration of things such as zinc and magnesium, if these are present in the anode.

Magnesium is too reactive and will not be electroprecipitated from an aqueous solution. As copper is less reactive than zinc, it will precipitate first, before any zinc does. If you place metal zinc into copper sulfate solution, the zinc will displace the copper and precipitate copper. The result is that as long as there is copper sulfate in the solution, the zinc will not precipitate. Eventually, the copper in the solution will be depleted and electrolysis will be less efficient, at which point the solution needs to be changed.

The metals with insoluble sulfates (e.g. lead, silver) will precipitate into a sludge from the anode. Similarly, noble metals like gold or platinum will be left as metal particles within the disintegrated anode, usually falling to the bottom of the electrolysis cell with the sulfates.

 

[Soulkeeper]

I think that answers my question.

 

[Soulkeeper]

Ok I just setup my electrolysis test
I'm not sure if it's doing what these things are supposed to do.
I'm seeing a loose copper sludge getting formed on the copper foil cathode instead of a solid plating.

I'm using a 12v psu as the supply, in a plastic tub with aqueous copper sulfate.

Anyone experimented with this before ?

My reason for attempting this was to use a bunch of random copper scraps and try to purify them into a single block/plate of copper.

 

[Soulkeeper]

I think i'm dialing it in. Running the psu thru different higher ohm resistors is having favorable results.

 

[Mark R]

You need to watch the current: Industrially, this is usually done at about 200 A/m2 - a high voltage is not required. 3-5 V should be sufficient and will avoid heating.

There are a few additives which might help a bit - add a bit of sulfuric acid (check out a hardware store for drain cleaner, sulfuric is a common one). Add a little bit of a thickener like gelatin (not so much that it sets, just enough to increase the viscosity a bit, this will help stop the copper falling off before it gets a chance to weld on), and a surfactant like dishwasher rinse agent (just a few drops).

 

[Soulkeeper]

I wasn't getting good results untill I purchased a variable power supply.
It seems (depending on the size of the piece) i'm having best results with just under 1v which works out to about 1 amp
Someone recommended 20amp per square foot, this seems inline with what i'm getting.
I added a bit of sulfuric acid, but havn't tried anything else yet.
I'm not sure where to get gelatin


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