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Reactivating Ferric Chloride etchant?
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Reactivating Ferric Chloride etchant?

by Agent24 on Tue Jan 25, 2011 8:26 pm

I recently ran out of Ferric Chloride - well not run out, but i've etched enough boards that the stuff doesn't work any more.

I thought about making the Cupric Chloride that everyone is talking about but then I read somewhere that one could just add more HCl to the old Ferric Chloride and it would reactivate it.

I bought a liter of 'Sprits of Salts" and I tried this today but it doesn't seem to work. I added about half the bottle to the leftover Ferric Chloride but all it did was turn my board a darker colour.

There seemed to be a very small amount of etching going on around the edge of the board after 10 minutes or so but usually there would be a lot more gone by that time.


Did I do something wrong, or is this just never going to work?
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Re: Reactivating Ferric Chloride etchant?

by dda on Wed Jan 26, 2011 4:04 am

Not going to work.
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Re: Reactivating Ferric Chloride etchant?

by Agent24 on Wed Jan 26, 2011 4:17 am

Why not?
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Re: Reactivating Ferric Chloride etchant?

by dda on Wed Jan 26, 2011 4:26 am

Ok, so check this out.

What you want to do is turn Fe2+ ions into Fe3+ ions.

To do that, you need to use a substance that is further down that table (on the left hand side of the equations) than Fe3+ (its at 0.77V).

Things that could in theory work would be: Ag+, Hg2 2+, NO3-, etc etc.

So, chemically, nitric acid might work... but hydrochloric has no chance.
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Re: Reactivating Ferric Chloride etchant?

by Agent24 on Wed Jan 26, 2011 5:46 am

Interesting, thanks for that.

I find it strange though that someone said it was possible to regenerate it (will find the link later) if as you say it's impossible

Unless they were missing part of the story out or just outright lying...

I don't suppose that running air through it to add oxygen would have any effect? (such as in the way the curpric chloride is supposed to be reactivated - see: http://www.instructables.com/id/Stop-us ... etter-etc/)
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Re: Reactivating Ferric Chloride etchant?

by dda on Wed Jan 26, 2011 6:45 am

Yes. using that table we can find

O2(g) + 4 H+ + 4 e− <-> 2 H2O

lower down the table. Sweet! So, thats cool. In theory that will work. In practice, im not sure what would be required.
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Re: Reactivating Ferric Chloride etchant?

by Agent24 on Wed Jan 26, 2011 7:57 am

I'll give that a try tomorrow and see what happens - I'll use an aquarium pump\bubbler as suggested in many places.

If it doesn't work I'll get some hydrogen peroxide and give the cupric chloride etchant a try instead.
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Re: Reactivating Ferric Chloride etchant?

by pstemari on Wed Jan 26, 2011 6:22 pm

Agent24 wrote:I'll give that a try tomorrow and see what happens - I'll use an aquarium pump\bubbler as suggested in many places.

If it doesn't work I'll get some hydrogen peroxide and give the cupric chloride etchant a try instead.


Aquarium bubbler to reconstitute the ferric chloride? I don't think so.

Here's the basic problem: While you used to have a solution with one part Fe+++ and three parts Cl-, you now have one part Fe++, one part Cu+ (or one half part Cu++) , and three parts Cl-. Adding HCl (H+ Cl-) isn't going to help. You need to remove Cu and oxidize the Fe++ back to Fe+++-

It's possible, but it's not going to be time or cost effective. You're essentially trying to reconstitute to wood from the ashes after the fire has burned out. You might be able to find a reprocessor for the used etchant, but I'm guessing the value of the dissolved copper isn't going to balance the cost of processing it. In order words, you'll need to pay to get rid of it.

This in a nutshell is why I haven't etched my own boards since I was in high school. The used etchant is highly toxic to plants and fish, and getting rid of it is a PITA.
--Paul

A wholly owned subsidiary of:
Persephone: DL R+W+B C 7 X L W C++ I++ T+ A E H++ S+ V-- F+ Q P B PA+ PL
Aldebaran: DM Rt H 5 Y L- W+ C+ I++ T++ A+++ E H++ S+ V+ F++ Q+ P B++ PA- PL--
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Re: Reactivating Ferric Chloride etchant?

by Agent24 on Thu Jan 27, 2011 8:03 pm

Well, I tried the air-bubbling idea yesterday but no luck - surprise, surprise

So today I got some hydrogen peroxide, and made a fresh batch of the curpric chloride etchant from Instructables.

Worked great!

Now all that remains to be seen is will it reactivate easily and work OK in a month or two when I next go to try something....
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