Electrochemistry Copper sulphate copper refining cell

[muld]

Hi there folks,
New member with big plans here. I'd like to ask for some input regarding a copper sulphate cell I'm currently constructing. I have planned to test most of the things I will ask about here, and I will be sure to post the results! If anyone would like to give some input on the ideas I have beforehand, as I am still gathering parts and supplies for my project, I'd love that - I'm really eager to get started. I'll apologize in advance for any dumb questions I might have, as I'll admit I haven't done as much reading as I wish (yet!).

Basic project outline: A copper sulphate copper refining cell. My plan is to smelt pure (electrical wire) copper together with a small amount of PM material, and electrolyze it to recover the PMs as anode sludge. The anode sludge is what I'm after, and the resulting copper doesn't have to be 99.99% pure as I only intend to use it as a PM 'solvent' in my furnace, as well as a sink for limited base metal contamination.


The power source: A 5V 30A rectified DC power supply. Unless my calculations are completely off, electrolyzing one kilogram of copper takes about 420 amp-hours, so I have been scouring the internet for a cheap low voltage-high current supply and came up with this (about $11+S/H on ebay!). As I plan to do smelts with at least a kilogram of copper in each, I'd like to be able to see the results within a day rather than weeks. One thing I won't be able to test by myself - how dangerous is this current? I am well aware that 30 amps can kill, but with such a low voltage, how dangerous will it be to be near the wires and such? I don't intend to handle anything in the setup while the power is on, but as a general precaution I'd like to know. Dry hands, and a power supply with short circuit protection built in - what could I expect if I accidentally touched a hot part?

The voltage: I know that 5V is excessively high for copper electrolysis, but it was the lowest voltage I could find with a high amperage for little money. I expect gold and platinum to drop out just fine, but is there any danger of losing palladium and silver if the electrolyte is running hot?
I expect the copper to grow in brittle crystal formations with this voltage, but this is perfect as it'll allow me to conveniently re-use it in subsequent smelting with new PM material.

The current and cathode: I haven't yet calculated the size of it, but I'd like to have a stainless steel plate as cathode, and scrape off the copper buildup now and then. If I'd use a plate, would both the sides of it count for surface area for current density? And would also my anode have to be large to accomodate a large cathode? I need to do my homework on current density...

The electrolyte: Here in Sweden, sulfuric acid is one of countless chemicals that aren't readily available to hobbyists - much to my dismay. Can I simply use a saturated copper sulphate solution, or is additional sulfuric acid required for the cell to work properly? I have tried using a saturated solution with a ~1A charger to successfully electrolyze copper, but I see that most copper cell guides have a significant amount of sulfuric acid in addition to the copper sulphate. This isn't a major hurdle as I could just split some copper sulphate with the same cell, using some graphite electrodes, albeit the concentration would be difficult to measure. Another safety question - how dangerous is the saturated copper sulphate electrolyte, in case of skin contact?

Additionally, I'd love if someone could point me in the direction of a guide to purifying the electrolyte. I have plenty of fresh copper sulphate available, but it would still be great to know how to remove unwanted base metals from it down the road.

Extra questions: What's an easy way to get rid of copper oxides? Unfortunately, I expect my crude furnace to produce PM-bearing copper anodes charred black with copper oxide, which I suspect will just fall to the bottom of my cell and mix with my values. Additionally, how hot should I expect the copper sulphate electrolyte to run with a 30A cell? After hours of searching for a 100A power supply, I found a small note implying that an electrolyte would be boiling and sputtering at such a high current, so I'm hoping that 30A might be feasible. Does increasing the volume of electrolyte reduce the risk for overheating?

This got a little longer than I expected, but I hope you don't mind! Any and all answers, comments, and questions are most welcome!

Thanks in advance, I look forward to my time here on Gold Refining Forum!

 

[Geo]

copper oxide is readily dissolved with hcl while leaving any PM's untouched.

 

[ericrm]

for the copper sulfate i would not worry too much about its toxicity as it sold as a wine additive... BUT and i put a very very big BUT when dealing with gold recovery your will not only have copper sulfate in your electrolite but a bunch of other metal that you will not neccessary be knowing about, and them could be very poisonnus (put glove and wear usual safety) also dont forget the hydrogene fume...

does someone know if anode slime are realy slimy or is it ,powdery and easymixed with the electrolite?

 

[Geo]

its referred to as slime but i think a better description would be sludge. ive never stuck my fingers in any to see if it was slimy but i imagine it would be kind of gritty.

 

[Jimmy]

Depends on whats in it. But generally it is like cake batter.
There is a post here somewhere about someone using a Microewave oven transformer as a welder. The output voltage is just right for copper electrowinning. Just need to add some diodes and capacitance. Im thinking about trying that myself.

 

[muld]

Hi folks, thanks for the replies!
Geo - Thanks for the tip, HCl for copper oxides sounds great! That's one of the few acids I believe I can get fairly easily here.

ericrm, I'm hoping the sludge will be relatively stationary at the bottom of the electrolyte, but judging from the copper oxides my copper-only cell dropped, it'll cloud up the electrolyte quite easily when disturbed - it doesn't stick together much. Thanks for the heads up about hydrogen, I'll be running it in a room that has a window in the ceiling so I should hopefully not explode the house... :lol:

Jimmy : I read about rewinding MOT's (Microwave Oven Transformers) as a homemade alternative too, but it seems like the effect loss is severe when you rectify it, and that there's a potential heat problem... I agree that it sounds really great for electrolysis though, it was exactly what I had in mind when I first started looking for a ~1V ~100A solution.
If you give it a shot, please let me know how it goes! I have an old microwave laying around, and have yet to see a better usage for it.

 

[Acid_Bath76]

I did some reading online last night, and found a good paper on Copper Electrowinning: Theoretical and Practical Design. It was published by the Southern African Institute of Mining and Metallurgy. It covers everything. There's also a neat nomenclature and reference section at the end, so you can make sense of some of the equations and whatnot. Hope this helps.

 

[nickvc]

I can see one problem with this idea. The running of any electrolytic cell demands a high grade feed stock so to get this to work you need at least 95%+ copper and probably higher to allow the copper crystals to form and adhere to the cathode, this is very important if your not using anode bags. The percentage left will contain a mix of metals with only a very small percentage been precious metals so to achieve any decent amount if values your going to have to run considerable volumes. For this to make financial sense you need to be able to sell the copper to cover the costs of running the cell, the slimes produced, aptly named , will still be mainly copper with traces of values and bigger amounts of other metals which will still need refining and the mix of metals will I believe be a challenge unless your very skilful and knowlegable.
If this is been done for the sake of knowledge and scientific interest then go for it but if your looking to make money I fear your going in the wrong direction unless you really can sell the copper recovered.

 

[NobleMetalWorks]

You can set up two cells, one for dirty material that you change the electrolyte on a regular basis (because it's dirty) and after casting an anode out of the plated out copper, refine it in the second cell.

There is another way you can do this, in combination or as a step that cuts out the need for a copper cell totally.

You can melt the copper and it's associated metals, into a homogeneous melt then atomize or corn flake it, then selectively digest in whatever acids best fit the situation, and refine further accordingly.

Cool HCl digestion will get rid of some base metals like tin for example

wash the left over material, incinerate, digest in Nitric acid. Cu, Pd and Ag will dissolve into solution and whatever leftover can be washed, dried, incinerated and digested in AR.

In this way you can separate the different metals and once you have accumulated the copper, you can then subject it to an electrolytic cell to take the copper to high purity, or you can further refine with acids.

The problem with small cells is that they are not tolerant to pollutants. It's the same concept I come across in salt water tanks. My friends always seem amazing that my tanks do so well. The reason is because they are huge, and very tolerant, because of the volume of water, to potential dangers. If a fish dies in a large tank, the resulting biological pollutants can be diluted enough so that they don't affect the other tank life. So one fish per 200 gallons is not going to cause a problem. But that same one fish that dies in a 30 gallon tank will turn the entire tank poisonous and cloudy.

If you are using a small electrolytic cell, even a small amount of pollutants can cause all kinds of problems, the percentage of pollutants will be high and can easily interfere with further refining. However, a larger cell the percentage will be far lower, the larger tank will be far more tolerant of pollutants.

Operating small electrolytic cells is an art. Those who do it spend a lot of time making sure their feed stock is clean, and keeping their solution pristine.

Scott

 

[goldsilverpro]

electrolyzing one kilogram of copper takes about 420 amp-hours

You figured the yield for Cu(l) instead of Cu(ll), which is incorrect.

For Cu(ll), it would be 1.185g/amp-hour or 843 amp-hours/kg

 

[g_axelsson]

Hej Muld och välkommen till forumet. Kul att se en till Svensk här, det finns ett par av oss här men vi är inte många. Var bor du? Jag håller till uppe i Umeå-trakten.

To get acids here in Sweden is not easy, depending on where you live. It took me a long time to find a place that sells nitric acid to individuals. The bad news is that you need a permit from Länsstyrelsen to be able to buy nitric or sulfuric acid, hydrochloric acid is easily bought from a paint shop (saltsyra). The good news is that you can apply for a permit easily, just state what you need it for, or if you have a company you could buy it without a permit.... at least that is what I've been told by a friend that checked it out last summer.

I've been looking at the sulfuric copper cell as a way to selectively leach the base metal from gold foils and I did a few trials ten years ago with varying results. No definitive results, it worked for a while but I had problems with the electrolyte... it dried out when I neglected it for a while.
But I haven't given up the thought of repeating the experiment. What I have learned the last years would probably give me a bigger chance to succeed.
I think that the secret behind success is to not see it as producing clean copper, but accept an end product that could be sold as brass. Most pins from e-scrap is gold plated brass, if you would get a clean copper from that feedstock you need to add a lot of copper sulphate to compensate for the zinc that goes into solution. But if you can get your cell to plate out zinc and copper in brass proportions than you could run it for longer times without worrying about the electrolyte.

In my experiment I used a solid gold wire (recovered from fingers) from the side of a jar down to the bottom. A bunch of gold plated pins on the bottom, covering and contacting the gold wire made up the cathode. The jar filled halfway with copper sulphate electrolyte. And from the top, a copper wire suspende as an anode. In the end I had transfered 50-100g of copper into a cauliflower looking mass. Anything loosely attached (didn't see anything) just fell down on the cathode again and got dissolved again.
I never ran the cell to completion and I still have it standing with the metal inside it, including the home made golden wire. Some day I'll either clean it up or restart the experiment.

Even if this isn't the optimal way to refine, it would give me a process that could be run with minimal gases and I could do some recovering / refining during the winter. If I could have a system that could deal with a couple of hundred grams a week then it would take care of all the pins I produce and have in storage.

Göran

 

[gold4mike]

I've been searching the forum lately hoping to learn how to recover the copper from approximately 30 buckets of solution I've accumulated from running pins in Poorman's nitric.

Not being a chemist, I'm not sure if what I now have is copper nitrate or copper sulphate.

I dissolve the pins using battery acid, lots of water (to keep crystal formation down) and sodium nitrate. We have many threads on the forum, including this one, for electrolytic recovery, but I want to make sure I'm following the right threads.

Can one of our chemists lead me in the right direction?

 

[Geo]

I've been searching the forum lately hoping to learn how to recover the copper from approximately 30 buckets of solution I've accumulated from running pins in Poorman's nitric.

Not being a chemist, I'm not sure if what I now have is copper nitrate or copper sulphate.

I dissolve the pins using battery acid, lots of water (to keep crystal formation down) and sodium nitrate. We have many threads on the forum, including this one, for electrolytic recovery, but I want to make sure I'm following the right threads.

Can one of our chemists lead me in the right direction?

hey mike, im no chemist,but im sure you have both copper nitrate and copper sulfate in solution. both are very similar in color,blue.without adding iron to the mix, zinc to cement may be your best bet as it works for both.since copper sulfate is more soluble than copper nitrate,you may be able to separate the two with careful evaporation.copper nitrate crystals should form first.since both crystal types are so similar though, you would have to rely on other means of monitoring than just visual.

sulfuric acid will dissolve copper oxide readily and as copper is oxidized in the presence of nitric acid,its a foregone conclusion that its present in the solution.

 

[gold4mike]

Rather than spend the money on zinc to recover copper to sell I was hoping to recover it electrolitically.

Will that be possible?

I wonder, too, if I might be overthinking it and could simply cement the copper on mild steel. I don't care if the copper is pure. I'd be happy to sell it as brass.

 

[Geo]

its been proven that you can pull the copper from solution with a cell like operation. steel wool is faster but tends to contaminate more.heavier steel will work fine but will cement the nickel and tin out with the copper.

i would try a small experiment on the solution with a couple of carbon rods out of "D" size batteries and a small appliance charger like the little black charger that has the electrical prongs built in (like a cell phone charger but with more amps).

 

[gold4mike]

Once the weather warms up this spring I'll start experimenting. I bought graphite from Jonn recently with this thought in mind. I have several power supplies I've saved from the myriad items I've received as scrap. There are many threads with enough info to give me a starting point.

Thank you and I'm sorry I have temporarily hijacked this thread!!

 

[jonn]

Gold4mike, your copper electrolyte can indeed be processed to extract your copper. If you use a copper starter sheet and can control the voltage you get a solid deposition. For electrowinning, you pull metal from solution with an inert anode such as graphite. Try to keep the voltage below 1.6 volts. For electrorefining, you refine a blister copper anode, try to keep your voltage below .4 volts, yes .4 not 4.0 volts. Your deposition is nice and solid. No need to remelt. I recommend thin copper starter sheets for the cathode material. Look at a chart on the voltage potential or reactivity series for metals, wiki has a good one. Copper is .34 volts. Electrolytic cells require a lot of mathematics as you change variables such as anode material, cathode material, types of metals in solution etc. With a fairly clean electrolyte and fairly pure anode, copper starter sheet, the voltage should be .34 volts. Your electrolyte could be tested for contaminants as you acquire the technology. Let's say your contaminant is mostly zinc, you could effectively focus on zinc extraction and purify the electrolyte. This could be reused for copper once again or... Once most of the metals are removed and your solution is mostly purified, why not reuse to dissolve base metals once again? There are many possibilities when working with electricity, just do the math and know your solutions. It is a precise science, but one well worth learning. Good luck and keep us posted, Jonn.