I plan on etching some PCBs with hydrochloric acid and hydrogen peroxide, which will therefore produce some kind of copper chloride (green color) which is highly toxic if released into the environnement (it may be useful as an herbicide, but I don't have any garden right now).

While cupric acid (obtained from hydrochloric acid, hydrogen peroxide and some PCBs etching) may be bubbled with air/oxygen to re-activate it to etch again other PCBs I'm not sure this may what I want and I seek suggestions in case I need to dispose of this solution.

Basically I heard (though none were actually on chemistry sites, except the 1st one):

  • Acid/Base neutralization: pour some baking soda to take care of the chloride
  • Pour some alluminium balls to get back some of the copper (didn't really understand how this works)
  • Copper electrolysis: basically get solid copper at the cathode, creating gaz at the anode and leaving (?) some residues that can be neutralized with baking soda (?)

Any insights on this? I think once the copper and chloride are taken care of, it shouldn't pose a huge problem to pour it down the drain or leave it outside to evaporate.


  1. Which metal should I choose for the anode / cathode ? In the first source it speaks about reactivity (and since copper is less reactive than hydrogen, copper is produced at the cathode). No idea about the metal I should use though.
  2. Would adding alluminium balls into the solution help make it more "eco-friendly" ?
  3. Any other suggestion is welcome



3 Answers 3


Regarding #2: Adding $\ce{Al}$ or $\ce{Mg}$ metal to $\ce{CuCl_2}$ solution reduces the $\ce{Cu_2^+}$ to $\ce{Cu}$, and you then have $\ce{Cu}$ metal (filter out and recover) and $\ce{AlCl_3}$ or $\ce{MgCl_2}$, respectively, in solution. Both solutions are safer in small quantities to flush down the drain.

Regarding #1: $\ce{2NaHCO3 + CuCl2 -> CuCO3 + 2NaCl + CO2 + H2O}$. $\ce{CuCO3}$ is insoluble, but should still be disposed of at an appropriate facility.

In both cases, you get an insoluble copper compound (or metal) rather than a soluble one.

  • $\begingroup$ Can I filter CuCO3 too or is it too small to filter? $\endgroup$
    – user51166
    Commented Jul 29, 2012 at 5:11
  • $\begingroup$ Sure, you can filter the CuCO3. $\endgroup$
    – user467
    Commented Jul 29, 2012 at 13:55
  • $\begingroup$ Thank you. Would I need some special kind of filter or something like a coffee filter is enough for this job (Cu / CuCO3)? $\endgroup$
    – user51166
    Commented Jul 29, 2012 at 19:05
  • $\begingroup$ I'd try a coffee filter, should work. $\endgroup$
    – user467
    Commented Jul 29, 2012 at 21:31
  • $\begingroup$ Reducing copper by aluminium or magnesium is nonsense. Thes metals would react much too vigoously! That process is done with eiger Zinc or, cheaper with the aid of iron (scrap iron). The handling of used pcb liquids is discussed since years ad nauseam in electronics literature! $\endgroup$
    – Georg
    Commented Feb 27, 2013 at 17:10

Depending on where you are, there may be places where you can hand over hazardous waste for proper treatment. E.g. in Germany the communal waste collection centres take properly labelled hazardous waste. For private stuff this is paid for by the general waste fees, so no extra fees are charged. If you do this on a commercial basis (= large scale), you'll have to pay for it, of course (but in this case you shouldn't have to ask how to deal with this in a forum...).

In any case, I'd recommend that you let (most of) the water in your solution evaporate so you get either a concentrated solution or the salt (chloride or carbonate) in order to reduce volume and mass of the hazardous waste.

  • $\begingroup$ Commercial users will sell that liquors to someone reprocessing the copper. Or after cementing the copper will sell the copper-sludge to an affinery. $\endgroup$
    – Georg
    Commented Feb 27, 2013 at 19:21
  • $\begingroup$ @Georg: you'll need to be quite above the baking-soda-for-neutralization scale in order to reach Cu amounts where you can ask that someone who comes and gets the stuff (under German/EU environmental regulations) should pay you... From the OP I'm not even sure he reaches the g Cu scale. $\endgroup$ Commented Feb 28, 2013 at 10:30

The best way to dispose of this is to use ascorbic acid (orange juice even?) to reduce the copper, causing it to precipitate as a metal. To deal with the corrosive iron chloride that is left you should add baking soda or calcium carbonate (limestone) to neutralize the liquid until the addition of either produces no bubbles.

  • $\begingroup$ I made blue water via electrolysis of water (with salt, using carbon rods wrapped in copper wire as electrodes), which I guess is copper chloride. I thought this was just going to be a fun little experiment; now I have to stay up late googling how to dispose of this. Anyway, I followed your instructions--squeezed a lime into the blue water and added baking soda until no more bubbles. Can I pour it down the drain now? It's changed to a light green color. $\endgroup$
    – ben
    Commented Nov 25, 2022 at 6:54

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