Hi,
I googled "neutralizing ferric chloride" and found the following Q&A article, which seems pertinent. In college, my physics was much better than my chemistry, so I'm not clear on the conclusion. That was a looong time ago, anyhow. Perhaps someone with better chemistry smarts could tell us if NaOH is the FeCl3 disposal solution.
It sounds like a ph meter may be a good addition to my lab. Does anyone have a good, CHEAP design for one that we could make into a PCB? J
Jim
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What is the best way to dispose of used ferric chloride PCB etchant?
I know of at least one method, diluting it and slowly pouring into the drain, but it can still stain and eat away metals in the pipes a bit. Is there something else I could use to possibly just "neutralize" it? I think an alkaline metal nitrate would work (Li;Na;K) or some other salt. That or maybe even just try to get the pH as neutral as possible.
∗3 years ago
Additional Details
Note: PCB is an acronym electrical engineers/hobbyists etc used to stand for PC-board, a.k.a Copper-clad board.
I also now realize a nitrate salt, as well as many other salts, would only form complex ions/ligands. Especially since the used ferric chloride would already contain complex ions due to the copper dissolved off the board (copper and chlorine like to do that a lot). Although, even that might bring the pH closer to 7.
3 years ago
Best Answer - Chosen by Asker
PCB enchant is Ferric Chloride (as you said), with a chemical formula of FeCl3...Iron (III) Chloride.
When you pour the Iron (III) Chloride on to a Copper-clad computer board with your circuit traced out on it, the enchant will eat away the undesired Copper by Oxidizing it to the very soluble CuCl2 and reducing the FeCl3 to FeCl2.
After you use your enchant, you will have a solution of FeCl2, CuCl2, and probably some remaining FeCl3.
All of these can be removed from solution by precipitating the metal ions out using a Hydroxide.
All of the Iron/Copper Chloride salts in your used etchant solution are quite soluble, but their Hydroxides are barely soluble.
if you add some Sodium Hydroxide ('lye', commonly found in drain cleaner), you can form the metal Hydroxide precipitates which can be filtered or decanted off, leaving a much milder solution behind.
FeCl3 (aq) + 3 NaOH (aq) --> Fe(OH)3 (s) + 3 NCl (aq)
FeCl2 (aq) + 2 NaOH (aq) --> Fe(OH)2 (s) + 2 NaCl (aq)
CuCl2 (aq) + 2 NaOH (aq) --> Cu(OH)2 (s) + 2 NaCl (aq)
Make sure and dilute the solution before you add the NaOH (preferably a NaOH solution). Dissolving NaOH in water is a very exothermic process, so the solution's temperature will rapidly rise if you are not careful. It is also a very bad idea to get any NaOH in your eyes or on your skin, so be careful but when used responsibly NaOH is fine.
When the Hydroxide precipitates are heated, they will form the metal Oxide salts. So for example, by heating Cu(OH)2, you will form CuO. The heat generated by the above reactions might also be enough to convert the Hydroxides into Oxides, so that is certainly a possibility but disposing of Fe2O3, FeO (or the combination of the two, Fe3O4), and CuO should be no problem.
The remaining NaCl solution will be no problem disposing of down the drain, as would any excess NaOH which happens to remain.
∗3 years ago
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From:
Homebrew_PCBs@yahoogroups.com [mailto:
Homebrew_PCBs@yahoogroups.com] On Behalf Of Philip Pemberton
Sent: Wednesday, February 03, 2010 5:46 AM
To:
Homebrew_PCBs@yahoogroups.comSubject: Re: [Homebrew_PCBs] Is Ferrich Chloride safer than Muriatic Acid / Peroxide?
Stefan Trethan wrote:
> Oxygen doesn't either, but accelerates any fire.
>
> I don't think there is a danger.
Though arguably that would make the HCl+H2O2 mix more risky near
furnaces, etc. (though isn't the combustion section of most modern
boilers effectively sealed off from the outside air?)
Academic point, really. I'd be more worried about high-concentration
HCl+H2O2 -- isn't that a so-called "piranha acid" mix, or am I thinking
of something else?
(But from what I've heard it's also a precursor to CuCl etchant, which
is -- AIUI -- about as hazardous as FeCl, so it all goes full-circle in
the end).
If you're using FeCl, I've been told mixing it with Plaster of Paris
will neutralise it (this was in the datasheet for a bottle of FeCl I
bought years ago). Though IIRC the more commonly accepted method is to
mix it with sodium carbonate or sodium bicarbonate until the pH drops a
little past neutral, then filter out the precipitate. The liquid is salt
water (NaCl+H2O) and the precipitate is an iron-copper mix of some
description.
Been a while since I did chemistry though, and I wasn't terrifically
good at it to begin with...
--
Phil.
ygroups@... <mailto:ygroups%40philpem.me.uk>
http://www.philpem.me.uk/[Non-text portions of this message have been removed]