semi off-topic: how to clean ferrichloride stains

Stain = Oxidation only appears on the surface, you have to sand it off a bit before applying Acetone.

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Acid. Try vinegar or oxalic acid. Think rust remover. For that matter, CLR sounds like yet another option.

Tim

-- Deep Fryer: A very philosophical monk. Website @

by

effect.

=46rom the blog of a very smart guy, Michael Covington:

(

"The other day, in our robotics lab, I gave a demonstration of making a printed circuit board. I used ferric chloride etchant because it doesn't require heating.

Unfortunately, I spilled a few drops of the etchant on a vinyl anti- static mat that was somewhat porous. As you know, ferric chloride is yellowish-brown, a lot like rust, and tends to stain everything it touches. So despite some cleanup attempts with water and various cleaning products, there was a stain.

Today (Dec. 22) I got the stain out, mostly. I made a paste of citric acid and water and left it on the stain for 2 hours. That removed about 80% of the stain.

I may go at it again with citric acid and hot water. I'm told that oxalic acid is more effective, and that it's sold as DAP Wood Bleach, but I didn't have any.

Addendum: I'm told that oxalic acid is also the active ingredient in Bar Keepers Friend powder (not liquid). If so, this should be just the thing for removing FeCl stains.

Another addendum: This source indicates that FeCl stains can be decolorized by phosphoric acid, i.e., Coca-Cola. I'll have to try that. As close as the nearest vending machine!"

-- Joe

(I microwave Ferric Chloride for really fast etching..and pressurize it too.)

Interesting but I avoid cleaning. :P If something gets stained, too bad. Chuck it in the garbage... Unless you splattered Ferric Chloride all over your new spectrum analyzer. :P

I use Ferric Chloride like a neat chemist. No mess. Ammonium Persulfate doesn't make yellowish stains. However, Ammonium P. can eat rugs.. Made a nasty hole one time :P

D from BC British Columbia Canada.

Doesn't seem so off-topic to me...assuming of course that you were using the ferric chloride to etch something electronic and not something else. ;-)

As others have pointed out, acid solvents work well on ferrous/ferric ions. Both ferric and ferrous hydroxide have very low solubility, but the acid removes the hydroxide part and lets the iron go into solution. If the thing you're cleaning can stand it, you can use (dilute) hydrochloric acid (muriatic acid), commonly available very cheaply at places that have masonry supplies, as it's used to clean up mortar splashes and the like. It works really fast to remove iron stains, generally won't hurt anything you'd put ferric chloride in, but like ferric chloride is best kept away from skin. I find it's also good to have a little HCl around to add to the ferric chloride solution, to insure the ferric stays in solution. Acid also keeps cuprous ion in solution.

I believe Zud is another cleanser that works well on iron stains: as I recall, it has a little oxalic acid in it.

Cheers, Tom

Get some commercial rust remover at the hardware store.

Rust stains on sinks can be got rid of with Naval Jelly, which is jellied phosphoric acid. Works right away.

Cheers,

Phil Hobbs

Use a deadly poison: Oxalic acid.

Any good reducing agent should do just fine.

Baking soda?

As previously suggested, oxalic acid is the stuff to use. Rhubarb leaves contain it, BTW.

Leon

I don't think so, but some judicious googling should find you some. Preferably less expensive that sodium bismuthate.

Yep. Also sodium sulfite (not sulfate) is good.

One commercial product made for this purpose (sold by Mega Electronics) consists of 100% oxalic acid powder. 100 grams of powder, dissolved in 500ml of warm water, is the recommended starting concentration). Immerse items and soak until the stain is removed.

For other sorts of iron stains (e.g. rust stains from a nail left a pocket) I've seen citric acid recommended.

In both cases, I believe that the principle is that the acid reduces (de-oxidizes) the iron, converting it back to a soluble form that can then be rinsed away.

Apply all appropriate safety precautions when working with these sots of organic acids (protective gloves and goggles for starters)!

No, I don't think that organic solvents would be helpful.

On Mar 2, 4:37 pm, snipped-for-privacy@radagast.org (Dave Platt) wrote: ...

It is, I believe, much simpler than that. It's simply that ferric and ferrous hydroxides each have such low solubility products that they don't dissolve readily in neutral water whose [OH-] is about 10^-7. By acidifying the water with a weak acid, you reduce the [OH-] to perhaps 10^-13 or 10^-14. That's a result of the characteristic of water that maintains [H+]*[OH-] at about 10^-14. That lets the ferric and ferrous dissolve much more readily.

Cheers, Tom

PH per se is a separate issue from redox. The most effective way to handle ferric chloride is by reduction. In well done cases you will get fe+2 in solution (or possibly if sufficiently extreme cases micro powder elemental iron in suspension, temporarily). If appropriate ionic species are provided you can remove most of the Cl- ions.

It is, but they are all equilibria. ;-)

Since we're going to invoke chemistry, I'm just going to go overboard and rattle off some stuff here: ;-)

Hydroxy: Fe(OH)3 Fe(3+) + 3 OH- pKs = 38.8 Fe(3+) + H2O FeOH(2+) + H+ pKa = 2.19 Fe(OH)(2+) + H2O Fe(OH)2(+) + H+ pKa = 2.41 Fe(OH)2(+) + H2O Fe(OH)3(aq) + H+ pKa = 7.97 (Note this doesn't include the solubility of the Fe(OH)3 species.) Chelates: Fe(3+) + EDTA(4-) [FeEDTA]- pKf = -25.1 Chlorides: Fe(3+) + Cl- FeCl(2+) pKf1 = -1.48 FeCl(2+) + Cl- FeCl2(+) pKf2 = -0.65 FeCl2(+) + Cl- FeCl3(aq) pKf3 = 1.00 Oxalates: Fe(3+) + C2O4(2-) [FeC2O4]+ pKf1 = -7.54 [FeC2O4]+ + C2O4(2-) [Fe(C2O4)2)]- pKf2 = -7.05 [Fe(C2O4)2]- + C2O4(2-) [Fe(C2O4)3)](3-) pKf3 = -5.41 (So total pKf = 20.00.) Citrate: Fe(3+) + Cit(3-) [FeCit](aq) pKf = -11.8 Redox: Fe(3+) + e- Fe(2+) Eo = 0.771 V SO4(2-) + H2O + 2e- SO3(2-) + 2OH- Eo = -0.936 V (Hmm, that's in alkali.)

So: Fe(OH)3 is damned insoluble; Fe(3+) is pretty acidic (as aqueous ions go); FeCl3 is somewhat more soluble, but it still takes a lot of chloride and acid to overcome the insolubility of Fe(OH)3; chelates like EDTA, et al., oxalate, citrate, etc. grab on real tight, solvating iron well; and a variety of reducing agents will suffice, but only if you get the iron into solution to react with it.

Tim

-- Deep Fryer: A very philosophical monk. Website @