Electrolytic copper refining cell

[modtheworld44]

Hey Shark!


Here's some pictures of my copper crystals,sorry it took so long.The biggest one is about a half dollar in size and 1-1 1/2 inches thick.I'm up to about 20+ pounds now in my five gallon bucket.I've got a nice little pile of gold foils in my anode basket.Thanks for sharing in this thread,it helped a lot in coming up with my new cell.Thanks for being a great friend. :mrgreen:



modtheworld44

 

[Shark]

That is some chunky copper! :shock:

That is pretty close to what I am thinking will come from a chloride based cell. Maybe not as big, but hard copper deposits that should drop away fairly easy.

 

[snoman701]

In other threads, a membrane is mentioned between the anode and the cathode. I have assumed this to be a membrane in excess of the filter bag to catch the slimes. Further, my assumption is that this membrane is used to keep only clean electrolyte around the cathode, to prevent passivation.

Can anyone describe this membrane and it's purpose?

Nickel still seems like the stopper here. Reported numbers of 3% by weight in pins, would only allow one to run a kg of pins / liter electrolyte. If I understand correctly, the "industrial" version of nickel treatment is essentially to first electrowin a lot of the copper, then the bismuth and antinomy, then add electrolyte back in to electrowin the arsenic (if present) as Cu3As. If your addition of electrolyte was correct, you should now have mostly nickel in your electrolyte. Now you concentrate the solution to concentrate out a nickel sulfate with lots of impurities (iron, calcium, bismuth, antinomy, etc). You've now got acid again, but it's contaminated with the organics.

Are there nickel specific ion exchange resins that will collect the nickel from sulfate solution? Even if you first electrowin a majority of the copper from solution. Then it's just a matter of adding copper back in to solution once the nickel has been removed. I can see this being successful if that is the case, but the process of concentrating nickel sulfate/sulfuric acid electrolyte to the point of crystallization is a stopper for me.

 

[Shark]

I haven't had time to try it yet, but by reducing the solution to 60% of the original volume, it should allow the nickle to drop out as a sulfate. You can then filter it and reuse the solution. I think 4metals mentioned it in a another manner as he was thinking about a lot larger cell than I used. I am thinking lower heat, in the 140F to 150F range, and slowly reducing the volume, which should be mainly the water in solution. I have had a lot going on lately and haven't got back to trying much with these cells other than a few small tests and a bit of reading. The key, I think, would be to remove as many metals as possible before hand and in the smelting process.

 

[FrugalRefiner]

Given the relatively low prices of copper and sulfuric in a copper cell compared to silver and nitric in a silver cell, is it worth the time and effort to recycle the electrolyte? I really don't know. I'm just posing the question.

Dave

 

[Shark]

Given the relatively low prices of copper and sulfuric in a copper cell compared to silver and nitric in a silver cell, is it worth the time and effort to recycle the electrolyte? I really don't know. I'm just posing the question.

Dave

With the majority of the material I am running, I am still not sure that recycling the solution is worth it on a small scale. By just removing the nickle, (in my case the majority of the contaminants) my electrolyte should gain a fairly longer useful life. The down side is that the time it takes to clean it up, I can make up new electrolyte, have it running, and enough time to see that the cell is running right again. I do have ideas on removing the nickle as a sulfate, while the solution is in a circulating system but I need time for some simple tests to see if some of the parts will hold up to the heat. So many things to try and not enough time.

 

[snoman701]

Given the relatively low prices of copper and sulfuric in a copper cell compared to silver and nitric in a silver cell, is it worth the time and effort to recycle the electrolyte? I really don't know. I'm just posing the question.

Dave

I just got 2 gallons of nitric for free. His outlook, "it costs me $0.50/lb, you helped me out elsewhere".

The acid is the cheap part, the costs being nearly negligible once you start to look at this from a business perspective. The waste, and the payroll are the expensive part. You have to treat the waste irregardless. If you can adsorb the nickel on to ion exchange resin, you get to use that electrolyte that much longer, at least until you end up with another contaminant fowling the electrolyte.

 

[Richard NL]

Modern Electroplating, 5th Edition:
http://allaboutmetallurgy.com/wp/wp-content/uploads/2017/03/Electroplating-M.pdf

Happy Christmas Richard.

 

[autumnwillow]

Is it advisable to cover the entire cell with a plastic wrap/cling wrap to prevent any evaporation which may lead to evolution of corrosive gases?

I have plenty of equipment that can oxidize easily in my office that I do not want to corrode and unfortunately there isn't room for my fume hood.

Shark have you tried melting the copper?

 

[Shark]

I wouldn't try running this cell in a office environment. While it dosen't seem as corrosive as Hydrochloric, my area had very little metal around the cells. I have melted small amounts of the recovered copper, but not by itself. I have added it back to other melts where I melted more PGM material along with some clean, fresh copper. I have a newer cell I want to try, but I can't seem to get caught up enough to try it.

 

[UrbanScrapper]

If you are using a computer power supply or any other DC power supply that is not adjustable, find a Buck Converter ( https://www.ebay.com/itm/DROK-DC-DC-Adjustable-Buck-Voltage-Converter-Stabilizer-Step-Down-Voltage-Red/311656730668?hash=item489030502c:g:I20AAOSwGXtXh6E0 ) This one (not my eBay store I just searched for one that shows V and A) would do the trick.

 

[Martijn]

Hi, first of all let me say thanks to 4metals for this excellent thread and shark for all the testing and info given. Really an awesome read and great info.

I'm starting a first test and not sure if the 50g/L is copper sulfate or sulfate made of 50 grams of copper? I've made 250g copper sulfate crystals. So i have enough for a small test cell of 600ml electrolyte. If I follow the recipe as I read it now, it would take only 30g of CuSO4 for this cell.

I calculated that about 40g of copper would make 100 gr of copper sufate so that would mean 125g of copper sulfate per liter to make it in that case.
I'm probably overthinking it but really not sure.

To give some more info on the intended test:
My anodes are made of pins with tiny bits of leftover gold plating from the sulfuric stripping cell and I want to see if I can squeeze the last bit of gold out. And get acquainted with the process. And find the right material for my anode bag. And learn much more... I hope.

The cell for the test is a stainless steel bowl in a holder to prevent knocking it over and spilling. All this will sit in a plastic basin for safety.
On top is a plastic beaker suspended with some holes in it all around the side and a very fine woven plastic fiber cloth as the anode bag, like those see-through window drapes. The bottom inch of the beaker is left intact to catch any slimes that might seep through.
My power supply is adjustable up to 40 volts and 3.5 Amps, also adjustable to a max limit. Only a few volts needed, so perfect for a small cell like shark's one.

I expect a lot of tin and/or zinc from the brass pins, and maybe some nickel from the 'underplating'. Dissolving one pin in nitric made some tin paste.
I just melted some pins in a graphite crucible in a charcoal fired, forced air furnace. Try saying that fast five times No major fluxing or oxygen sparging.
Only used a little borax.
So the anode will probably passivate or foul the electrolyte pretty fast, but thats what testing is for right? I will need to be able to clean the dirty electrolyte too.
Practice makes perfect.
Once i have this process kind of under control, I intend to fill the basket with cleaner copper shot like the silver cell. Has anyone tried that? I saw the stainless steel bowl in this thread, but not clear if he used shot or not.

But if anyone can clarify the amount of copper sulfate needed per liter, would be great. I'm confused.

Martijn.

 

[Shark]

This is where I got the formula I used to calculate how to make up my small cell solutions. It has been quite a while since I worked with these but it was a lot of fun and made for a very nice change of pace from chemically working with gold.

https://www.thinktink.com/stack/volumes/voliii/consumbl/cplatmix.htm

I used pins in several of my anodes and they work, downside was the nickle under plating played havoc with the electrolyte pretty quick.

 

[Kaiser613]

Concerning nickel fouling the electrolyte,

Why couldn't you just increase the voltage and plate out the nickel, zinc, and other dissolved impurities, with graphite anode, cathode either graphite or nickel, until solution is depleted of dissolved metal and reuse?

 

[Martijn]

I was thinking about testing that. Have half a liter pale blue green electrolyte.

 

[anachronism]

I was thinking about testing that. Have half a liter pale blue green electrolyte.

Probably not worth the time spent and equipment cost required to learn how its done.

 

[Kaiser613]

So I went to the local hobbyist electronic shop today and left with a (not so cheap) 3a rectifier my first cell is producing lots of bubbles from the cathode, presumably hydrogen? I don't think this is supposed to happen if the cell is operating properly for out metal deposition purposes? Why would this be happening? I'm thinking not enough copper in solution?

 

[anachronism]

What's your cathode material and your electrolyte?

 

[Kaiser613]

Cathode is a piece of clean copper grounding wire, anode is a peice of dirty copper pipe, along with some small pieces of brass and copper held together in a piece of synthetic mesh fabric

 

[Kaiser613]

My first cell (vertical in a half gallon jar , submerged cathode suspended anode) did nothing but produce a few liters of black waste solution and a lot of bubbles, upon closer inspection the only plating that occured was the tinned wire connected to the cathode gained a copper finish, I feel solution conductivity was the limiting factor. So today i put together a new cell, (have no cuso4 on hand so spent a day reacting copper into diluted sulphuric until decently saturated) in my first cell I used a peace of synthetic mesh fabric rubber banded across the mouth of the jar as a "basket" for the anode material, but the fabric had significant capillary action, enough that the edges hanging outside the jar continuously dripped electrolyte, this reminded me of salt bridges in galvanic cells, so I put together the cell pictured (if my pictures show up, in having problems uploading pictures taken on my phone)the anode is a piece of copper pipe and the cathode is a piece of titanium tubing, as it runs (at Max voltage for my psu about 30v) the anode half cell solution saturates with copper sulfate until it collects as powder at bottom of half cell, and cathode solution depletes of copper, the first time it was ran (pictured) the depleted solution changed from aqua blue to reddish brown, bubbling at cathode is minimal while solution is blue but intensifies as solution quality drops, deposition quality is medium high, but moving cathode knocks off the bumpier pieces. I then switched the electrodes to opposite half cells, the red-brown solution has sinced been restored to saturated blue, the other solution has been again depleted but is a milky white now, the "salt bridge" is passing current but does not seem to be transporting any ions, this whole cell is very high resistance and runs quite hot, the fabric dries out frequently, walking inside for 15 minutes burnt a mark onto the synthic fabric.