Recycling copper, working at scale. Suggestions.

I would call a scrap dealer and ask if they want the stuff as-is
you won't get a lot of cash,
but you avoid the hassle and potential hand/finger cuts.
Or
teach a kid some entrepreneurship

Keep enough of the easy to strip wires for a little chemistry etc.
10 moles (635.46g) should last a chemistry lifetime.
Thick copper strands with pvc insulation intact will resist long term storage corrosion the best.

Quote: Originally posted by Rainwater

As for chemical conversion, HCl + sunlight takes forever, until you hook up a solar panel.

Nitric acid just seems wasteful. However, most other acids are going to need some help.


I would actually prefer a nice copper compound as a product rather than copper metal. Sulfate is always useful. But oxide, chloride or carbonate would be acceptable too.

My best thoughts so far are to strip the wires until they are exposed even if not fully clean. Then join together to make anode. Then electrorefine in a solution of copper sulfate. The problem here is that the resultant copper won't necessarily be in the most useful form.

I have time. There is no rush. I have been hanging on to the bag for a decade already.

---

RogueRose - 25-11-2024 at 18:38

Liquid Nitrogen? Dry Ice & acetone bath? Cool the insulation & hit it with a hammer?

---

averageaussie - 25-11-2024 at 18:49

electrorefining like this? https://encrypted-tbn0.gstatic.com/images?q=tbn:ANd9GcQ-u8kJ...
or something else?
if you want copper metal -> copper compounds, acid might be a not bad idea, copper is pretty acid resistant though...
apparently concentrated HCl with oxidisers present can attack copper... seems like anecdotal evidence at best, likely someone added a nitrate salt to HCl.
electrolysis in a sulfuric acid solution seems like your best bet.
if you can melt the copper down, you could maybe pour it from a height into a bucket of water to make copper shot, then use that (higher surface area) in the electrolysis bath. dunno if thats gonna work though.
apparently, you can use a mix of acetic acid and hydrogen peroxide to attack metallic copper. can this make peracetic acid? apparently. is it worth a shot? maybe. (https://crystalverse.com/copper-acetate-crystals/)
good luck.

---

clearly_not_atara - 25-11-2024 at 20:34

^Incredible formatting glitch. I think you borked the whole page.

I think you can leach copper with ammonium persulfate and then precipitate the Cu(NH3)4SO4 by adding alcohol.

---

Precipitates - 25-11-2024 at 20:55

Quote: Originally posted by j_sum1

Then electrorefine in a solution of copper sulfate. The problem here is that the resultant copper won't necessarily be in the most useful form.

20 kg of copper could make some big old copper sulphate crystals!

Useful? No. Nice ornament? Yes!

---

j_sum1 - 25-11-2024 at 21:10

Quote: Originally posted by Precipitates

Quote: Originally posted by j_sum1   Then electrorefine in a solution of copper sulfate. The problem here is that the resultant copper won't necessarily be in the most useful form. 20 kg of copper could make some big old copper sulphate crystals! Useful? No. Nice ornament? Yes!

Electrorefining gives metallic copper -- in whatever form it deposits on to the cathode. In my experience it is dendritic, but by controlling surface properties and current density, it is possible to have nice sheets or even a powder that sloughs off.

Off topic (or maybe not). Look up the artwork "Seizure" by Roger Hiorns


I am liking the idea of HCl and air. HCl is my cheapest acid per mole of H+. I have a spare aquarium bubbler. I think I can find a way to tame stray HCl vapours. I will do some trial runs, but this might be a winner.
(OTOH, locally available hardware store HCl is typically contaminated with Ti -- of all things. And distilling several litres might not be a fun thing.)

---

Sulaiman - 25-11-2024 at 22:24

Quote: Originally posted by j_sum1

...I would actually prefer a nice copper compound as a product rather than copper metal. Sulfate is always useful. But oxide, chloride or carbonate would be acceptable too. My best thoughts so far are to strip the wires until they are exposed even if not fully clean. Then join together to make anode. Then electrorefine in a solution of copper sulfate. The problem here is that the resultant copper won't necessarily be in the most useful form. I have time. There is no rush. I have been hanging on to the bag for a decade already.

your copper has probably survived a decade of poor storage posing little risk during that period.
All soluble copper salts are potential biohazards.
It is a lot easier to produce copper compounds from pure copper than it is to produce pure copper from copper compounds.
Copper can be used as an electrode or wire.

Solvent compatibility is a significant factor in materials choice for electrical insulation.
Unless you wash in solvent many times, your pure copper will have a plastic film coating.

Just a few thoughts

---

Rainwater - 26-11-2024 at 00:23

The jacket on the wire will probably an THHN or THWN. Both of these are a two layer nylon outter jacket surrounding a PVC jacket. Chemical compatible with petro and resistant to most solvents at room temperature.

Best bet will be a good flat knife, cut resistance gloves, and some heat.
Heating the wire up to about 80-100c will make the insulation very easy to remove

---

j_sum1 - 26-11-2024 at 01:25

The bulk of the wire has ancient rubber insulation more than 70 years old. The rubber is cracked and perished. The copoer itself is partly oxidised. The old wire is twin single core with about 2mm diameter. That is thick enough to make flexing difficult. It also means there is quite a bit of copper there - which is why I hung on to it. I added my own wiring scrap to the pile over the years. And there was some more modern wiring in the house as well, which is why it is a tangled mix.

Yeah, I could get a couple of bucks for it as scrap. But there seemed some aesthetic value in recycling it myself if I can.
Making something out of scrap is the first goal.
Clearing the garage is the second.
Purity and making money are not big considerations. OTOH, I don't want to spend hundreds on nitric acid. Doing it cheaply seems like a better way to go.

---

bnull - 26-11-2024 at 05:59

Quote: Originally posted by averageaussie

apparently concentrated HCl with oxidisers present can attack copper... seems like anecdotal evidence at best, likely someone added a nitrate salt to HCl.

10% HCl does it pretty well. I never had any issues with the watery stuff from the hardware store. As for the anecdotal part, put NaCl brine or HCl in a test tube and add solid copper sulfate. When it has dissolved, drop some copper wire or scraps and leave the test tube alone for one hour. Then examine the copper and the solution, which will be deep brown.

Adding a nitrate would a very bad idea: NO₂ is given off, whether you can smell it or not, and it gets worse with heating. First hand experience.

The crux of the biscuit here is the combination of the oxidising properties of copper(ii) chloride with the formation of chloride complexes ([CuCl_n]^(n+1)- perhaps, I forgot how much is n). It goes like this:$$Cu(s)+CuCl_2(aq) \rightarrow 2CuCl(aq)$$ for the dissolution of metallic copper, and $$4CuCl(aq)+4HCl(aq)+O_2(g) \rightarrow 4CuCl_2(aq)+2H_2O(l)$$ for the regeneration with air. You can even use an alkaline chloride (table salt, for example) in the first reaction (there must be an excess of chloride ions, no matter who supplies them) and reserve the hydrochloric acid to dissolve the newly formed copper hydroxide after the regeneration.

Ullman's Encyclopedia of Industrial Chemistry, chapter on copper compounds, section on copper(i) chloride:

Quote:

The copper(I) chloride solution is produced, for example, by mixing a copper(II) chloride solution with metallic copper in the presence of hydrochloric acid or sodium chloride. The colorless to brown solution is stable only in the absence of air

because air oxidises Cu(i) to Cu(ii).

An example of process:

1. Make a copper(ii) chloride or sulfate solution with extra chloride ions. If you have a way to contain the vapors of hydrochloric acid, use it. If not, sodium or potassium chloride will do, and you can save hydrochloric acid for the regeneration;
   
2. Add copper. Since the insulation in the old ones is cracked, beat them a few times with a stick to remove most of the flakes. The ones that can be stripped should be stripped.
   
3. Leave the solution alone for some time. Check in each day to see what color it is. If deep brown, it's time for regeneration.
   
4. Regenerate the etchant. If you used hydrochloric acid in the beginning, simply stick a hose from the aquarium air pump to the bottom of the solution. It goes from deep brown to bright green, when it's time to leave it alone again to dissolve more copper. If you used an alkaline chloride, stick the air hose the same way as before, and when it becomes bright green turn off the pump and add hydrochloric acid to dissolve the hydroxide and oxychloride and whatever else that precipitated.
   

You can leave it unattended for however long you want because there is no risk of foaming or hydrogen gas or production of a corrosive spray. No electricity is used except during regeneration, which is so simple that you can do it while reading a book, as long as you can see the color change.

---

Sir_Gawain - 26-11-2024 at 06:00

By my calculations it would take about 50 L of HCl, or 15 L of sulfuric acid, to dissolve all the copper (assuming about 15kg of pure metal present). Where I live, that’s about 100 USD of acid, but you may not access to that much acid at a reasonable price.

Put the acid and copper into a large container and add an air pump. I don’t know how long it will take, but it should eventually dissolve. Copper sulfate would be easier to crystallize out than copper chloride, but sulfuric acid is harder to get. I suppose you could precipitate with sodium carbonate, but I can’t imagine filtering that much blue sludge.

---

Texium - 26-11-2024 at 08:11

If you have access to relatively concentrated hydrogen peroxide (~10% should be fine, 30% would be better but not required) you can speed up the reaction with HCl quite significantly. I even made a significant amount of copper chloride back in the day using HCl and 3% peroxide, but the resulting solution was very dilute and took a long time to evaporate, so I wouldn’t recommend that for large scale work. Bubbling air through is certainly more economical, but also significantly slower.

---

charley1957 - 26-11-2024 at 09:03

I stripped the insulation from a LOT of copper wire by drilling a hole through a 2 X 4 piece of lumber just larger than the wire, maybe an inch from the edge. Then take a drywall screw and screw it into the lumber from the edge such that the tip of the screw emerges into the hole you drilled. Then insert your wire into the hole and draw it through, adjusting the drywall screw until you get a good stripping action. The 2 X 4 lumber is best secured to something solid. You will probably need to do some preparatory stripping to get this to work, or it’s possible this same technique might work on two-conductor sheathed wire, called Romex here in the US. I saw this on YouTube and I couldn’t believe how well it worked, and why I waited so long to try it. Once I saw how well it worked I had it all done in just an hour or so, and I had a LOT of wire. Give it a whirl, doesn’t take much time and if it doesn’t work for you, it hasn’t cost you anything but a little time.

---

Fulmen - 26-11-2024 at 11:48

There is another process that uses ammonia, CO2 and air to leech copper. It forms a highly soluble ammonia-carbonate complex using air as the oxidant. Once saturated the liquid is boiled down to produce basic copper carbonate, the ammonia can be captured and reused. A simpler recipe is to use a mixture of ammonia and ammonium carbonate and just discard the ammonia.

---

Sir_Gawain - 26-11-2024 at 12:20

Quote: Originally posted by Fulmen

There is another process that uses ammonia, CO2 and air to leech copper. It forms a highly soluble ammonia-carbonate complex using air as the oxidant. Once saturated the liquid is boiled down to produce basic copper carbonate, the ammonia can be captured and reused. A simpler recipe is to use a mixture of ammonia and ammonium carbonate and just discard the ammonia.

I don’t think this will work very well. I’ve tried it before, and the reaction is extremely slow.

---

averageaussie - 26-11-2024 at 13:51

Thank you for explaining that to me Bnull, that clears things up a lot.

---

Dr.Bob - 26-11-2024 at 16:47

Anything other than just recycling the metal is going to lose value compared to just recycling it. I end up collecting lots of metal scrap each year or so, and end up taking a pile of metals to the junk yard each year, I have gotten over $100 for a few bags of copper wire (insulated and not very clean), and over $200 for a large pile of steel and stainless. I could see using a few kilos for chemistry, but trying to recycle it via acid, solvents or other means would cost more than the wires value, plus be an environmental diaster. Most scrap yards and recyclers have special equipent to more easily recycle it.

[Edited on 27-11-2024 by Dr.Bob]

---

j_sum1 - 26-11-2024 at 17:52

Scrap prices locally are feeble. I am likely to get about $20 for my bag if I take it in. Principally because it is not clean.
OTOH, If I buy $20 of HCl and invest some time, I should be able to get a reasonable stockpile of a copper compound. I will need to do some math to work out how much of my scrap I will use up.

---

Fulmen - 27-11-2024 at 00:34

Quote: Originally posted by Sir_Gawain

the reaction is extremely slow.

It works, even if it's a bit slow. IIRC the initial reaction is slow, but increases a bit once you have copper in solution. But any air-powered reaction will be slow, that's just the price to pay for free oxidizer. So what? Time is cheap if you don't have to monitor the reaction. I don't think sulfuric acid and air will be any faster.

One benefit of this reaction is that it produces a dense copper carbonate powder of uniform composition, something that is impossible with direct precipitation.

---

clearly_not_atara - 2-12-2024 at 18:32

You might be able to kickstart the reaction with ammonium persulfate like I suggested earlier. It's Cu(NH3)2(+) that gets oxidized by oxygen to Cu(NH3)4(2+)

---

Sulaiman - 3-12-2024 at 03:50

I think that if you 'burn' the copper eg on a BBQ grill) to form an oxide layer it will dissolve in HCl much easier.
When the reaction slows, burn the copper again.

---

Fulmen - 3-12-2024 at 06:11

That should work, but I doubt it will be fast. And it will require more work and energy. For a small batch it's probably doable but for 20kg? Air oxidation is slow, but it can be done with little effort and a small aquarium air pump. I've done this both with ammonia/CO2 and sulfuric acid, albeit not on such quantities.

---

pesco - 3-12-2024 at 08:59

Chemicals pricing and availability depends on your location. In most places HCl is the cheapest mineral acid. Can be even cheaper, if you make it yourself and you can easily do it in huge amounts for free or nearly free. Just pyrolyze some PVC, preferably uPVC or CPVC and you'll have gallons of HCl.



From that pile of Cu I would select some somewhat clean pieces and
1) electrolyze in NaCl solution to obtain Cu₂O or CuO. Best precursor to Cu salts.
2) melt some cables (purer) to get nice electrode for electrochemistry or cementation of Ag

Other bits, dirty, tiny wires, difficult to strip or mixed with Sn/Fe I would stick in sealed steel paint can or similar and pyrolyze. Gasses pass through water to scrub HCl and then into the fire to neutralize. If the fire is HOT (500+ °C) and the gasses stay there for around 1-2 seconds then all the nasties will get destroyed.
Once pyrolyzed and Cu exposed flood it with HCl.
PET bottles outside work very well. PET is UV stable and bottles wont disintegrate after a while spilling the content. I have PET bottles in full sun for couple years and they seem to be still like new, just dirty . I keep the bottles inside old aquarium placed on its side. That way rain doesn't get into the bottles, even very strong wind wont knock them down and the temperature get a bit higher when Sun is out speeding up reactions.
HCl works initially slow, but once some Cu dissolves the dissolution speeds up. If you place and aerator in the bottles then it is pretty fast. Aquarium airpumps work great, they are cheap and need very little electricity. Wouldn't bother with peroxide, too expensive in these amounts and not necessary, especially if you are not in a hurry.

Dissolution by HCl is not as fast as HNO₃, but the later is nearly everywhere difficult to obtain and WAY more expensive than HCl.

---

Fulmen - 3-12-2024 at 11:18

HCl + nitrates should work as a substitute for nitric acid.

---

pesco - 6-12-2024 at 05:51

All acids attack copper. In a way
Even dilute cold sulfuric or acetic will do, however it will take a while.

Copper is readily oxidised by dissolved oxygen, either in liquid on moist air. Both come down to O₂ in presence of H₂O.
Once oxidized pretty much any acid will attack the oxide.
This is how patina is formed. By dissolving copper oxide by carbonic acid.

Long time ago, for shits ang giggles I poured some 10% vinegar in a bottle, put some coper wire in it. In couple months time it got deep blue.

HCl is much faster than most. Out of "common" acids only nitric and concentrated sulfuric are faster.
Once you have some CuCl₂ in solution it works as a catalyst.

Cu + CuCl₂ -> 2CuCl
4CuCl + 4HCl + O₂ → 4CuCl₂ + 2H₂O

In effect HCl is pretty fast in dissolving copper as long as there is free oxygen dissolved in the mixture and just atmospheric O₂ is enough.


I remember reading on this forum ingenious way one of the members developed to produce copper acetate. It involved flask with acetic acid topped with reflux column with copper bits packed into it and air supplied below. As acetic acid evaporates it passes, together with fresh air (O_s), through copper bits, then condensates above and drips down to the flask on the way dissolving copper already oxidises by O_s.

[Edited on 6-12-2024 by pesco]

[Edited on 6-12-2024 by pesco]

[Edited on 6-12-2024 by pesco]

---

teodor - 6-12-2024 at 07:14

But why you don't consider persulfate as was suggested already. The price?

---

Rainwater - 6-12-2024 at 15:51

Monday, i put 1g of fine copper strands into 250ml of di water with 1g NaCl and an air bubbler.
Today, I have no copper metal left in the beaker. But a lite green percipitate i assume is copper carbonate

---

Fulmen - 7-12-2024 at 02:38

@Rainwater: Well done, now you just have to repeat it 20'000 times :-)

@teodor: We're talking 20kg of copper here, have you calculated the amount of persulfate needed to dissolve that? It's not going to be cheap with any available oxidizer (besides air). Basically you have the choice between expensive and slow.

---

bnull - 7-12-2024 at 09:08

@Rainwater: Try a more concentrated solution (1 g of NaCl in 10 mL of water, for example); the more chloride ions, the better. The precipitate is apparently a mixture of basic copper carbonate and copper hydroxide.

I was reading a patent the other day but forgot to jot down the number. Searching for it today, I found one (US2046937, "Process for the preparation of copper compounds from metallic copper") that looks more interesting. It uses copper (ii) chloride ammonium chloride. I'll test a variation of it, starting today.

---

Rainwater - 7-12-2024 at 14:32

Naa. I keep mine as metal and toss it in the mash as needed.
Just trying something as its the closest to an experiment ive been able to do in months.

---

DraconicAcid - 7-12-2024 at 15:19

I'm honestly considering a career change. Despite my decades in an academic setting, and electrician's salary would be much nicer.

---

teodor - 8-12-2024 at 02:49

Quote: Originally posted by Fulmen

@teodor: We're talking 20kg of copper here, have you calculated the amount of persulfate needed to dissolve that? It's not going to be cheap with any available oxidizer (besides air). Basically you have the choice between expensive and slow.

Yes, but for working at scale it probably could be formed in situ by electrolisys of (NH)4SO4 solution in H2SO4. If copper is present in the bath it will be converted to CuSO4. I doubt you can make it more economical pumping air with electricity instead of oxidising with electricity.

Also with proper activation persulfate can conver many organic compounds to CO2, but I am not sure about the insulation.

[Edited on 8-12-2024 by teodor]

---

Precipitates - 8-12-2024 at 06:32

Quote: Originally posted by Fulmen

It's not going to be cheap with any available oxidizer (besides air). Basically you have the choice between expensive and slow.

Bleach is pretty cheap.

---

pesco - 8-12-2024 at 08:17

Quote: Originally posted by teodor

Yes, but for working at scale it probably could be formed in situ by electrolisys of (NH)4SO4 solution in H2SO4. If copper is present in the bath it will be converted to CuSO4. I doubt you can make it more economical pumping air with electricity instead of oxidising with electricity. Also with proper activation persulfate can conver many organic compounds to CO2, but I am not sure about the insulation. [Edited on 8-12-2024 by teodor]

Don't know about the costs electricity in electrolysis vs pumping air.
Need to be calculated/tested by somebody with inclination and a bit of spare time

Point is that you don't have to pump air. It only speeds the reaction up. If you don't use airpumps then the oxygen will naturally diffuse into solution and oxidize copper anyway. It will just take a bit longer. A bit longer doesn't mean years. It is literally "a bit" longer. Done it, seen it.


If you really want to have some fun with fiddling around and save (tiny amount of) money then rig up small device. A bit of a plastic shaft/tube with two fans linked via string or threaded rod. The top fan will be turned by wind and it will "power" the bottom fan which, half submerged, will agitate surface of the solution. That should be pretty much as efficient as air pump and no electricity involved.

Small aquarium airpumps have wattage of 2W to maybe 8W for pretty powerful one. Lets assume you have bigger one, 5W model, and you want to run it 24/7.
Average 1kWh costs nowadays around £0.25 in UK.

1000/5 = 200 so on 1kWh you can run this pump for 200h

1 week = 24*7 = 168h

cost of electricity for 1 week = (168*£0.25)/200 = £0.21

A month of constant running such pump costs less than £1.
And hassle free, stick the airstone in, turn the pump on and forget about it for few weeks.
Not really worth messing about

---

bnull - 9-12-2024 at 12:24

Quote: Originally posted by bnull

I was reading a patent the other day but forgot to jot down the number. Searching for it today, I found one (US2046937, "Process for the preparation of copper compounds from metallic copper") that looks more interesting. It uses copper (ii) chloride ammonium chloride. I'll test a variation of it, starting today.

At the time of my post above (14h08m), I dissolved about 1 gram of sodium chloride (table salt, nothing fancy) and 1 gram of copper (ii) sulfate pentahydrate in the smallest quantity of reverse-osmosis water. Since I don't have ammonium chloride because it is restricted here (O_o), I used 2 grams of ammonium bicarbonate and about 6 mL of 15% HCl to neutralize the stuff. The solution was a weak green-blue on top of a white precipitate, perhaps an anti-caking agent like silicon dioxide.

I cut about 50 cm of varnished copper wire from an old de-Gaussing coil. After burning off the insulation on a spirit lamp and removing the charred residue with a wood sandpaper, I made it into a multi-turn loop and inserted it into the test tube in a way that most of it remained submerged. The loop slipped to the bottom of the tube. I used used some expletives (bugger that, I won't fish it) and left the tube alone for about eight hours.

Later that night (0h32m):



Notice the three liquid phases. Green is relatively rich in oxygen, so most if not all of the copper is copper (ii). Brown has a considerable quantity of copper (i) and is very poor in oxygen. A clear, transparent solution means that all the copper present is copper (i), with no oxygen whatsoever in solution. The white stuff is apparently silicon dioxide. Most of the copper wire was gone. The distribution of the phases was affected by the diffusion rate of oxygen through the solution. The relative size of the phases is about 8 green to 3 brown to 1 clear.

I attached another length of shiny copper wire to a small motor and used it as a stirrer to mix the three phases and dissolve more copper. The solution became yellowish, as an unfiltered wheat beer (straw yellow). I added 10 drops of 15% HCl to a small section of the top phase without disturbing the rest of the solution. It immediately turned brown. Today, two days later, the solution is a dark amber color with a greenish precipitate of oxychloride or hydroxide or basic carbonate, or a mixture of the three.

The presence of ammonium cations indeed increases the rate at which copper dissolves. The patent may be right about a 50-fold increase after all .

On hindsight, I could have made ammonium chloride from table salt and ammonium bicarbonate and used the solution, which would need less HCl.

---

Fulmen - 9-12-2024 at 13:27

This looks slightly relevant: https://www.sciencedirect.com/science/article/pii/S266679082...

Seems like both chlorides, carbonates and sulfates are suitable candidates.

The carbonate process still has an ace up it's sleeve imho. It can be reduced to very pure CuO that's the perfect raw material for a number of other copper compounds. But if this isn't a problem the chloride process looks like a very promising candidate.

---

j_sum1 - 9-12-2024 at 14:51

Thanks for all the suggestions. I have not read through all of them yet. It looks like I have a few trial runs to set up in my lab. I hope to get to that in the next couple of days.

---

Dr.Bob - 9-12-2024 at 16:44

You may have already seen this, but similar to what you are doing:

Also see http://www.sciencemadness.org/talk/viewthread.php?tid=160306...

"I have another idea: copper can be dissolved in ammonia solution with ammonium chloride (or even sodium chloride).
Resulting tetraammine copper(II) chloride should decompose when heated to copper(II) chloride and ammonia.

Dissolution in ammonia works better with "ammonia water" (24%), but diluted household grade ammonia also works, but more slowly, I once made tetraammine copper perchlorate from 10% ammonia and lithium perchlorate. Thin copper wire (incompletely) dissolved in several hours. Edit: in 24 hours, actually.

What I'm not sure is whether decomposition will produce copper chloride or copper oxide and HCl."

---

Sulaiman - 10-12-2024 at 04:15

I like the idea of an air pump and bubbler, if only to circulate the liquid,
removing reaction products away from the copper , allowing the oxidising components to get to the copper.
The extra dissolved oxygen will of course help with the oxidation.
I would avoid bleach due to the sodium ions.

---