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Author: Subject: How do I recrystallize ferric chloride?
Carbon8
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[*] posted on 24-5-2018 at 12:42
How do I recrystallize ferric chloride?


Does anyone have any ideas about how to recrystallize FeCl3 from an acidic etching solution. I have had a fan blowing on an evaporation dish of the stuff for a week and the fluid level has barely budged.

I haven't found much information online about low-energy or low-cost methods of purifying FeCl3. Is that because there are none?
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[*] posted on 24-5-2018 at 12:55


You simply can't, FeCl3 is extremely deliquescent and will absorb moisture from atmosphere.

[Edited on 24/05/18 by fusso]




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[*] posted on 24-5-2018 at 13:28


I used this method to dry holmium oxide,

Place your solution into a crystallization dish, over a beaker of water. Boil the water and allow the steam to contact the bottom of the dish. This will keep your dish at about 60C and not exceeding 100C. This ensures that your solution will evaporate quickly without decomposing or being etched into the dish by heat. I highly recommend this method.




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[*] posted on 24-5-2018 at 16:18


Thanks to all for your comments.

The etching solution lists its ingredients as ferric chloride and HCl.

I don't have a compelling reason for wanting crystals, I just want to see if it's possible. I will give the warming treatment a try, although I've read that there is a risk that the ferric chloride will decompose to ferrous chloride and HCl.
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[*] posted on 24-5-2018 at 17:02


If it does decompose find out at what temperature. If its above 100C then you will be fine using steam



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[*] posted on 30-5-2018 at 00:22


Update: FeCl3 can be dried by fan according to Nilered
Seems like where you live is very humid or simply the weather is very humid at that time.




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[*] posted on 1-6-2018 at 05:51


Comments, first avoid sunlight (or diffused light) otherwise with aqueous Fe(lll) at low pH (best at pH 3) as you could have some photo-fenton chemistry afoot (see Eq 4 at http://cdn.intechopen.com/pdfs/29377/InTech-Fundamental_mech... ) forming ferrous.

Next, limit oxygen exposure with light, as any created Fe(ll) (especially if complexed with chloride, see https://www.sciencedirect.com/science/article/pii/S001670371... ) with O2 and H+ will likely undergo an electrochemical reaction leading to a basic ferric chloride.

Unwanted ferrous can also be created in the presence of other transition metal salts (for example, a copper ion impurity). A redox couple equilibrium may form resulting in an equilibrium concentration of ferrous, which will be re-established as ferrous is consumed per any of the above.

In short, salts of increasingly anodic metals, and further those that are considered transition metals or related, may produce unexpected products (see, for example, http://www.sciencemadness.org/talk/viewthread.php?tid=83114#... ).

[Edited on 1-6-2018 by AJKOER]
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[*] posted on 1-6-2018 at 11:01


Unfortunately ferric chloride is one of those substances that simply refuses to crystallise.

Heating it to dryness decomposes it, so that's not an option.

If you leave it out to dry, it'll either sit there not losing any water, or suck more from the air and remain liquid.

A reaction using anhydrous ferric chloride as a catalyst was shown by NurdRage.
He stuck dried iron wool in a flask of dry toluene and bubbled dry chlorine into it - the anhydrous ferric chloride was formed in situ, catalysing the formation of chlorotoluene(s).

If you could keep the air out, perhaps that'd be a way to produce ferric chloride crystals, depending on IF it would ever crystallise out of toluene/chlorotoluene(s) at all.

That's all random speculation as i never tried it myself.

Edit:

Presumably if that was tried, the toluene would get chlorinated at every position, producing god-knows-what as a by-product. Probably something Bad.

[Edited on 1-6-2018 by aga]




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[*] posted on 1-6-2018 at 11:11


You could probably dry it with azeotropic distillation with toluene in a dean stark trap. Then dissolve it in anhydrous acetone or ethanol and crystallize it from that solution.
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[*] posted on 1-6-2018 at 11:32


I wonder ...

If it's soluble in toluene, perhaps you can get crystals by just distilling out most of the toluene, sealing the bottle and chilling it.

I've used ferric chloride for 37 years for making PCBs.
The first stuff i ever bought was military surplus.
It came double-bagged in thick plastic, and was dry (as i saw it then).

It certainly would be nice to find a way to get ferric chloride drier, and smaller.

Amateur gold refiners produce a lot of this stuff in their final 'stock pot'.

It'd be useful to find a way to process it into a small bag of orange-brown crystals (or mush) rather than a 5 gallon bucket of trouser-staining goop.

I do believe you've sparked something off here Carbon8 ;)




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[*] posted on 1-6-2018 at 11:55


I wasn't aware it was soluble in toluene but that makes since knowing what else it is soluble in. I assume something like hexane or other nonpolar could be added to lower the solubility and crystallize it out of toluene.

It just occurred to me that using toluene might be slightly problematic. Would the ferric chloride chlorinate the toluene to some degree while its refuluxing for 1-2 hours?
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[*] posted on 1-6-2018 at 12:47


Toluene distills quickly, so most of it should be gone in a simple distillation in about 30 mins.
(i'm imagining small quantities, not 60-gallon flasks)

Iron probably hangs onto the chloride ion far better than some weakling sub-metal organic could ever hope for.

Cool/stopper the flask as quick as possible and maybe FeCl3 crystals ?

Not sure anyone knows .... now there is a Challenge !

Superb suggestions walruslover69.

Edit:

A simple experiment to see if it is soluble to any extent in toluene would be to stick a few mls of toluene in a test tube, add the same mls of water, then put a few drops of FeCl3 in.

The water/toluene should separate into distinct layers.

If there's any brown colour in the upper layer after a bit of mixing, bob's your uncle.

Further Edit:

If anyone has a test tube, some water, toluene and ferric chloride, please try this and post a photo ASAP.

If not, i'll move the separation-from-paint-thinner to make more toluene to the head of the queue.

Oh, and then distill it. Important that part is.

[Edited on 1-6-2018 by aga]




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[*] posted on 1-6-2018 at 15:11


I didn't have any ferric chloride laying around so I just quickly dissolved some iron oxide in hydrochloric acid and treated it with h2o2. I took 5ish ml and added it to the cylinder along with 5 ml of toluene. I swirled it around and it appears that none of iron went into the toluene layer.

Wikipedia says that it is very soluble in diethyl ether so I tried the exact same thing and got the exact same result of no iron being present in the organic layer.

THE PLOT THICKENS!

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[*] posted on 1-6-2018 at 16:03


Put it in a airtight box or bag with an even more hygroscopic substance.
Google 'dessicator' for inspiration.




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[*] posted on 1-6-2018 at 20:21


Method for preparing anhydrous iron chlorides
US1938461A https://patents.google.com/patent/US1938461

[This also describes some older processes that maybe useful for other routes]

:::::: since dehydration of the tetrahydrate results in hydrolysis and only basic salts are left. Likewise, attempts to dehydratethe ferric chloride hexahydrate, FeClsnGI-IzO, result in hydrolysis, There are methods for preparing the anhydrous ferrous salt from ferrous chloride tetrahydrate for instance the double ammonium salt may be formed by dissolving the tetrahydrate .in' an ammonium chloride solution, evaporating the solution of the double salt to dryness and heating the'residue in the absence of air. The waterand ammonium chloride escape and-leave the anhydrous ferrous chloride behind. ::::::

..."by evaporatinga ferrous chloride solution at an elevated temperature so as to precipitatethe dihydrate crystals and effecting a separation of the crystals from the mother liquor at a temperature above about 90 C. I have found that it is possible, in the substantial absence of air or oxygen, to dehydrate the ferrous chloride 'dihydrate compound directly without "hydrolysis, and without departing from the solid phase, in order to secure substantially amhydrous ferrous chloride...

... I have found that anhydrous ferric chloride can most advantageously be produced by simply chlorinating anhydrous ferrous chloride...

...The anhydrous ferrous chloride thus prepared may then be passed in intimate contact-with dry chlorine gas to .chlorinate it substantially to anhydrous ferric chloride. In effecting this chlorination, I have foundit expedient to pulverize the anhydrous ferrous salt so that substantially'all of it will pass through a standard Tyler 40-mesh screen. It is also preferable that. during chlorinationheat be supplied to the salt so as to raise its temperature to between about 140 and 190-C.', preferably about 175 0., since this materially reduces the time required for chlorination, and increases the percentage conversion to the ferric salt. This method for the preparation of. anhydrous ferric chloride possesses advantages not enjoyed bythe processes heretofore developed."

[Edited on 2-6-2018 by violet sin]




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[*] posted on 1-6-2018 at 20:54


Yeah, you can't get anhydrous FeCl3 once it's already hydrated. It's similar to AlCl3 in that respect. You might be able to get hydrate crystals though.

The trouble is that HCl will leave along with water as you try and dry it, and so it will leave a mixture of iron oxychlorides or whatever they're called, rather than solely FeCl3.




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[*] posted on 1-6-2018 at 23:05


Quote: Originally posted by walruslover69  
... it appears that none of iron went into the toluene layer.

Thanks for the experiment and the great photo !

Shame it doesn't go into the toluene :(

Quote: Originally posted by Melgar  
... will leave a mixture of iron oxychlorides or whatever they're called, rather than solely FeCl3.

Hmm. Good point.

Quote: Originally posted by phlogiston  
Put it in a airtight box or bag with an even more hygroscopic substance.
Google 'dessicator' for inspiration.

Doesn't work for this compound, as stated above.

Google 'ferric chloride' for more inspiration ;)

This patent: https://patents.google.com/patent/CN103991911A/en
says "ferric trichloride solution is heated, boiled, cooled and crystallized to obtain high purity ferric trichloride crystal."

Could be rubbish. Could be true.

Another googled snippet mentioned 'ferric chloride hexahydrate", which is presumably crystalline.

I suppose the conditions must be acidic and rammed with chloride ions to keep the compound intact, so the question is how to get to that state without having a lot of water lying around.




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[*] posted on 2-6-2018 at 11:07


Aga, "the ferric trichloride is dissolved in **water** and then filtered to prepare a ferric trichloride solution; the ferric trichloride solution is heated, boiled, cooled and crystallized to obtain high purity ferric trichloride crystal."

"The method of preparing a high-purity ferric chloride claim, wherein said ferric chloride to ferric chloride hexahydrate crystals."

---------------

So this is not what you want. The patent I linked does make anhydrous ferric (and ferrous) chloride. But the problem is, there is a need to chlorinate the ferrous salt, but it's under 200℃. Still it's not ideal. There was mentioned the decomposition of ammonium chloride/ ferric chloride double salt in vacuum to get ferric chloride anhydrous. Check it out.

I surely concede, nothing is perfect for every home chemist. but I am going to try mine at some point in prep for a project.




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[*] posted on 2-6-2018 at 11:55


Basically the OP wants crystals from already-dissolved ferric chloride.

Me too - got lots of it and very little usable space to keep it, hence my interest in reducing that solution to reusable crystals (even mush).

NurdRage has a few good videos about recycling PCB etching ferric chloride solution, but focus more on 100% recycling rather than retaining ferric chloride as such.




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[*] posted on 11-6-2018 at 09:16


An idea:
* Make the FeCl3 solution as concentrated as possible by evaporation.
* Add the double volume of 96% ethanol to it. (The solubility of FeCl3 in ethanol is only some 10% lower than in water.)
* Absorb the water by the addition of water free CuSO4 of MgSO4 or the like. (Tricky: does the water absorber have enough strength to push the FeCl3 into the ethanol?)
* Filter the solution to remove the hydrated water absorber.
* Distill off the ethanol. (This is tricky: will the dissolved FeCl3 now also decompose in one way or another?)
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[*] posted on 12-6-2018 at 05:27


The reason that no FeCl3 from aqueous solution is extracted into an organic layer is due to the ionic nature of the hydrated compound in solution.

If you take anhydrous FeCl3, which is a black solid, looking very much like iodine, then you can dissolve this in quite a few organic solvents. The same is true for anhydrous CuCl2 and anhydrous AlCl3. These anhydrous compounds are covalent compounds.

In water you get metallic ions, partially coordinated to chloride ions and water molecules, giving rise to ionic species in solution and these do not extract into an organic (apolar) layer.

BTW, I have never seen crystalline hydrated ferric chloride. The stuff which you can buy at electronics shops as copper etchant is a solid, consisting of little amorphous spheres, the size of peanuts, which dissolve exceptionally well in water and give a solution which easily hydrolyses to basic chloride. The anhydrous compound is crystalline, it consists of many small glittering dark grey/black crystals, which also dissolve very well in water.

I expect that the best you can get with hydrated ferric chloride is a cake of amorphous solid when you boil down the solution of ferric chloride from strong hydrochloric acid and assure that the solid material has a lot of HCl-gas around it when dried. Maybe you can get a solid if you boil down to an acidic syrup from conc. HCl and the nearly solid syrup is stored in a tightly closed container in which also some NaOH and/or conc. H2SO4 is stored in a separate dish.

[Edited on 12-6-18 by woelen]




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[*] posted on 12-6-2018 at 07:28


Going off that. Shouldn't you be able to precipitate and possibility crystallize it out of solution by adding ethanol or IPA?
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[*] posted on 12-6-2018 at 16:11


Quote: Originally posted by walruslover69  
Going off that. Shouldn't you be able to precipitate and possibility crystallize it out of solution by adding ethanol or IPA?

Well, that's the basis of my idea two posts above this post, but as woelen explains, you won't dehydrolyse the iron(III) by the addition of ethanol or the like. Put otherwise, ethanol has a weaker affinity for H2O than Fe3+ which exists as an aquo or chloroaquo complex and keeps water softly bound around that complex.

Probably, when you add water to an FeCl3 solution in ethanol, a layer will separate out, containing basic FeCl3 solution in water.

I wonder what happens when you add CaCl2.0H2O to an acid saturated FeCl3 solution.
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[*] posted on 12-6-2018 at 20:37


Quote: Originally posted by Bezaleel  

I wonder what happens when you add CaCl2.0H2O to an acid saturated FeCl3 solution.


I am thinking a fair bit of HCl fuming would result.

I think the increased chloride saturation and dehydrating properties of calcium chloride would force HCl out of solution, but the FeCl3 will remain hydrated.
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[*] posted on 13-6-2018 at 05:41


Quote: Originally posted by Bezaleel  

Well, that's the basis of my idea two posts above this post, but as woelen explains, you won't dehydrolyse the iron(III) by the addition of ethanol or the like. Put otherwise, ethanol has a weaker affinity for H2O than Fe3+ which exists as an aquo or chloroaquo complex and keeps water softly bound around that complex.

Probably, when you add water to an FeCl3 solution in ethanol, a layer will separate out, containing basic FeCl3 solution in water.

I wonder what happens when you add CaCl2.0H2O to an acid saturated FeCl3 solution.


I was originally under the impression that hydrated FeCl3 would be insoluble in organic solvents like ethanol, IPA, acetone etc... but from some research it appears the hydrate is soluble in most semi polar solvents just not to the extent that the anhydrous form is.

Does anyone have any solubility data for FeCl3 6H2O? I have been trying to find some but I am unable to find any actual numbers except for the solubility in water.

I think my original idea of azeotropic distillation might be the most promising.

My rough idea of the procedure is as follows.

add a substantial amount of anhydrous IPA to a concentrated solution of FeCl3. Ideally all of the water should be able to distill over as the IPA-water azeotrope leaving only a solution of FeCl3 6H2O in IPA.

Evaporating the IPA might produce solid FeCl3 6H2O crystals.

If not, the addition of a miscible organic solvent like toluene or something could be added to precipitate the FeCl3 6H2O

Second thought- Doing the azeotropic distillation with toluene instead of IPA might work out better.
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