Recovery of copper from electroplating & etching solutions

A. Hi Raphael.
I haven't done it, but this is what I would try if I received no other advice. I would get a get a roll of vinyl or fiberglass screening, rinse it well, and trim it to the width of the tank, and unroll it to cover the bottom and the two ends of the tank. Then I would get a bag of ice, probably double bag it to be safe, and put it in the tank. 12 or 24 hours later I would take out the bag and try to remove any crystallization by lifting the screening.

Actually, as always, I would experiment with a beaker of the solution rather than the 40 gallons first.

I think the solubility difference between 68 °F and 40 °F or so would be sufficient. You might even save the crystals in case you overdid it :-)
Luck & Regards,


Ted Mooney, P.E. RET
Striving to live Aloha
finishing.com - Pine Beach, New Jersey

A. Hi Nazish. I'm not sure quite what you mean by 'then multiplying by 10'. Do you mean you are supposed to scale up your numbers to recover the copper from 100 ml? If so, I LOVE your science teacher, as 'scaling up' is an important lesson that many people in industry never learned! (We have many threads from professionals here where they say something like "we had 10000 liters of waste we were trying to treat, so we started by adding 1500 liters of this, and 1700 liters of that and 800 liters of a third thing -- but it's not treated correctly, so how many hundred liters of some fourth thing should we try?" And we despair that they've created 14000 liters of a witches brew when they should have been experimenting with a single beaker).

I don't know what type of information you are looking for, but the copper will spontaneously plate out onto a wad of soap-free steel wool [on eBay or Amazon]. You could see how much steel wool you need, then scale up for the larger batch. Another routine would be to add caustic soda or a milder alkaline material like washing soda [on eBay or Amazon] to increase the pH until the copper precipitates out as an oxide/hydroxide, then do your scale up of how much you'll need for the bigger batch. Good luck.

A. Hi Ken. The copper can presumably be electroplated out of the solution with a recovery cell, or removed via ion-exchange. But if you are looking for the simplest recovery of copper from etchant, you could perhaps consider sulfuric acid-peroxide etching because the copper solubility is so temperature sensitive that recovery of copper sulphate crystals is possible continuously by recirculating the solution between the hot etching tank and a cold crystallization tank.

The site's supporting advertisers will contact you privately regarding sourcing of such recovery systems. Good luck.

Regards,

A. Electrochemical cells (electrolytic recovery cells) can be no more complicated than they need to be, and may not be too expensive for you.

It depends on the solution chemistry and other factors, but electrolytic recovery may be more or less expensive or practical than such alternatives as ion-exchange and crystallization. If you are using sulfuric acid plus peroxide for your etching, it is possible to operate at a high temperature and periodically or continuously cool the solution to precipitate copper sulphate crystals. Good luck. Regards.

A. In my own experiments, I have gotten very good results plating copper out of hydrogen peroxide/sulfuric PCB board etch. At current densities of 5 - 10 amps/square foot, a nice ductile foil was obtained that peeled easily from a stainless steel cathode.

It was necessary to neutralize the peroxide with sodium metabisulfite [on eBay or Amazon] before plating commenced - without it, no Cu deposited. The electrolyte also dissolved a stainless steel anode - you have to use a titanium or precious metal oxide coated anode.

All in all, encouraging, but there are significant costs that may be greater than what you're incurring now. Do your own tests and see. Good luck.

A. Hi Goran, try to use graphite for the positive "anode", use a low current density on it. Tell me the result.

A. Why not use a copper cathode in your electrochemical recovery, and then you can just add what you recover from the solution to existing copper? Only the anode in this application needs to be inert, as far as I know. Hope this helps.

Regards, Henry

A. Hi Jane. I would agree with Henry.

Just as one would not use an ultrafilter as a gravel screen, very high surface area porous carbon cathodes should probably not be used for primary electrolytic recovery because of the problem you are having.

If you need copper removal to extremely low levels you can use your porous carbon anodes as a secondary polishing system, but use a primary electrolytic recovery cell with conventional copper anodes or strippable stainless steel anodes as a first step. Alternately you could consider a recovery system with copper wool cathodes, because they can be melted down when full. Good luck!

A. Hi Peter. Only Retec, or your Retec manual, can answer that question without doing an analysis I suppose. But I thought the idea was that they are an expanded or reticulated pure copper designed to be smelted. Evoqua seems to have discontinued the Retec line. Get that manual quick, while you can! :-)
Good luck.

A. You may want to explore using ammonium carbonate to dissolve the copper and not attack the steel. It may be possible to electrowin the copper from this solution and then re-use it to strip more copper.

A. You would be better reclaiming the copper from whatever liquid you are treating that is generating the sludge.

A. Dave is absolutely spot on! Plating the copper out and/or concentrating it with ion exchange while it is still a soluble ion is so much more practical & doable than precipitating it first, contaminating it, then trying to redissolve it for plating out.
Luck & Regards,


Ted Mooney, P.E. RET
Striving to live Aloha
finishing.com - Pine Beach, New Jersey

A. Hi Bhautik.

I assume you mean that the bath contained sulfuric acid and was used to clean copper, and that it was "part of an electroplating line", not that it was an electroplating tank? Please spend a paragraph clarifying the particulars, because we don't know enough about your situation to make a proper suggestion -- presumably there is other stuff (hydrogen peroxide, ammonia, detergent?) in that cleaning bath? Thanks.

Regards,

A. You can likely plate it out, perhaps after the addition of some grain refiner.

A. Copper can be recovered from spent etching solution by simple displacement reaction with less noble metals,; fine iron powder or zinc powder [on eBay or Amazon] will turn any copper sulphate (base of most copper plating solutions) or copper chloride (etching solution) to copper powder and zinc sulphate (colorless) or zinc chloride (colorless),

There is a video on youtube by Robert Murray about making copper nanoparticles using a household blender, iron powder and a capping agent like ascorbic acid. According to his information this can be done for just about any metal, so I will be trying it with spent nickel plating solutions in the future.

A. I don't think there's enough difference in the redox potentials of Fe and Ni that that would work.

You might try Al dust [on eBay or Amazon].

Dave Wichern
Consultant - The Bronx, New York

A. Today scrap copper is about £3 per kilo and ascorbic acid about £40 so I am a little skeptical about the proposed recovery method.
The two simple methods are cementation on scrap iron or plating out.
Remember that etching solutions are there to dissolve copper so whatever oxidising component is used must be completely used up or neutralised first.

Interesting video but using a domestic spoon (and a food blender!) in a lab is a major crime -- and the echo makes an otherwise excellent commentary almost indecipherable.

Geoff Smith
Hampshire, England

A. Hi Lunje. Since you say you are new to this, step 1 is to make sure you are using the right anode material, i.e., phosphorized copper, which dissolves slower and minimizes the problem. Good luck.

Regards,

A. It appears that you may need a larger cell to plate out the excess copper.