Sciencemadness Discussion Board - Inexpensive synthesis of Ferric Chloride

Inexpensive synthesis of Ferric Chloride

Anomalous - 3-11-2013 at 17:28

I'm thinking red iron oxide, and 28% muriatic acid.

6HCl + Fe2O3 -> 2FeCl3 + 3H2O

Given 2268g of Fe2O3 (14.175 mol) I calculate that I should need about 2.89 gallons of the muriatic acid.

Will the yield be anhydrous FeCl3 in solution, or will I get the hexahydrate?

Is there a more cost-effective approach to ferric chloride? It appears to me that the reaction above should cost about 1/4 what it costs to buy ferric chloride.

Thoughts?

[Edited on 4-11-2013 by Anomalous]

Crowfjord - 3-11-2013 at 17:56

You would have solution of Fe³⁺ and Cl^- in aqueous solution. If you boiled it down, you would get the hexahydrate, which would decompose back to Fe₂O₃ if you heated further and drove off the rest of the water IIRC.

[Edited on 4-11-2013 by Crowfjord]

barley81 - 3-11-2013 at 18:15

Keep in mind that red iron oxide from suppliers often reacts too slowly with aqueous solutions to be of much synthetic use. Calcined red iron oxide dissolves very slowly in acid.

Anomalous - 3-11-2013 at 18:17

Quote: Originally posted by Crowfjord

You would have solution of Fe³⁺ and Cl^- in aqueous solution. If you boiled it down, you would get the hexahydrate, which would decompose back to Fe₂O₃ if you heated further and drove off the rest of the water IIRC.

That sounds right to me. I know you can't get the anhydrous simply by cooking off the water.

Thanks!

[Edited on 4-11-2013 by Anomalous]

Anomalous - 3-11-2013 at 18:43

Quote: Originally posted by barley81

Keep in mind that red iron oxide from suppliers often reacts too slowly with aqueous solutions to be of much synthetic use. Calcined red iron oxide dissolves very slowly in acid.

Hmm... I suppose I'll just have to try it. The supplier I use claims its iron(iii) oxide is from a natural source. Perhaps the reaction will be catalyzed by other oxide impurities?

We'll see. Thanks.

elementcollector1 - 3-11-2013 at 20:08

Doesn't this form FeCl₂, not 3?

barley81 - 3-11-2013 at 20:21

No, because iron (III) oxide cannot oxidize chloride ion.

elementcollector1 - 3-11-2013 at 20:39

I was thinking of iron metal - my mistake.

Oscilllator - 4-11-2013 at 00:04

The iron oxide I obtained from ebay dissolved extremely slowly. I stained a test tube with some iron oxide, and then left it to soak in nitric acid. The acid was still there over a week later.

woelen - 4-11-2013 at 00:11

Nearly all sources of Fe2O3 sell calcined oxide. This is very inert and hardly dissolves in acid. It takes forever to dissolve even a small amount of this oxide in a large excess amount of acid. This method of making a solution of ferric chloride is not useful at all. Well before the acid is used up (even when still more than half of the acid is still remaining) the reaction comes to a near halt.

AJKOER - 4-11-2013 at 04:53

Try and dissolve the iron in a mixture of HCl and H2O2 and a touch of sea salt (or vinegar and bleach appears to work, but the products now include an acetate). Even dilute starting solutions may work for you. I suspect some electrochemistry afoot (search for my comments/references on a so-called 'bleach battery' where now Iron metal replaces Aluminum and keep a new 100% plated copper penny in the mix as well), hence the progression with even dilute reactants involving the corrosive oxidation of a metal in the presence of an oxygen source (HOCl) releasing Cl2 into the solution. Basically, you are using chlorine water, more specifically, Hypochlorous acid as the fuel. The HOCl apparently enables the slow but steady attack of the Fe.

Beware and take precautions, you will get a strong Chlorine smell and the solution of Ferric chloride, even starting with dilute reactants, which can become quite corrosive. Note, FeCl3 is commonly employed as an etching agent for circuit boards and the like.

What is amazing here is what a strong acid cannot do, a weak one does in the right conditions!
-----------------------------------------------

A related history involves the action of an oxygen source on Copper in the presence of aqueous ammonia. The debate among pundits proceeded apparently for many many decades. The latest consensus is that the reaction appears to proceed along the lines of a electrochemical oxidation of a metal in the presence of O2 coupled with some of the usual copper/ammonia chemistry.

[Edited on 4-11-2013 by AJKOER]

blogfast25 - 4-11-2013 at 06:25

Dissolve scrap iron in an excess 37 % HCl, filter off insolubles. Oxidise the FeCl2 solution with 35 % H2O2, slowly and with constant cooling.

Evaporate the FeCl3 solution, while maintaining an acid reserve to prevent hydrolysis. FeCl3 is very soluble and difficult to get to crystallise. It's all been explained somewhere on this forum. UTSF.

blargish - 4-11-2013 at 08:54

A solution of FeCl₂ made from iron and hydrochloric acid can even be oxidized to FeCl₃ by bubbling air through it. Just leaving a solution of FeCl₂ exposed to air will oxidize it after a bit.

blogfast25 - 4-11-2013 at 10:08

Quote: Originally posted by blargish

A solution of FeCl₂ made from iron and hydrochloric acid can even be oxidized to FeCl₃ by bubbling air through it. Just leaving a solution of FeCl₂ exposed to air will oxidize it after a bit.

Except... it takes forever! Fe(II) oxidises to Fe(III) much faster in alkaline conditions but even then with air oxygen it's a slow boat to China. The trouble with air oxidation of Fe(II) is that it's a nuisance when you don't want it to happen and far too slow when you need it to happen.

[Edited on 4-11-2013 by blogfast25]

bbartlog - 4-11-2013 at 10:33

The other issue with oxidizing a solution of FeCl2 via air is that unless you have an excess of HCl in the solution, you'll get some mixture of FeCl3 and oxides. In fact the formation of Fe2O3 may predominate over the formation of any FeCl3 if there is no HCl in the solution, just base on my experience with solutions of FeCl2 exposed to air (they don't turn red, but instead gradually develop brown gunk).

blargish - 4-11-2013 at 10:36

Quote: Originally posted by blogfast25

Quote: Originally posted by blargish

A solution of FeCl₂ made from iron and hydrochloric acid can even be oxidized to FeCl₃ by bubbling air through it. Just leaving a solution of FeCl₂ exposed to air will oxidize it after a bit.

Well... this is the inexpensive synthesis of Ferric Chloride

. I think grabbing a straw and blowing bubbles through the solution is as inexpensive as it gets hehe. You're right though, it would take quite a while

DraconicAcid - 4-11-2013 at 10:43

Quote: Originally posted by blargish

Quote: Originally posted by blogfast25

Quote: Originally posted by blargish

A solution of FeCl₂ made from iron and hydrochloric acid can even be oxidized to FeCl₃ by bubbling air through it. Just leaving a solution of FeCl₂ exposed to air will oxidize it after a bit.

Well... this is the inexpensive synthesis of Ferric Chloride

. I think grabbing a straw and blowing bubbles through the solution is as inexpensive as it gets hehe. You're right though, it would take quite a while

Add a small amount of weak base to make the solution barely basic, allow it to oxidize by air, and then acidify to dissolve the sludge.

blargish - 4-11-2013 at 11:02

Quote: Originally posted by bbartlog

The other issue with oxidizing a solution of FeCl2 via air is that unless you have an excess of HCl in the solution, you'll get some mixture of FeCl3 and oxides. In fact the formation of Fe2O3 may predominate over the formation of any FeCl3 if there is no HCl in the solution, just base on my experience with solutions of FeCl2 exposed to air (they don't turn red, but instead gradually develop brown gunk).

I believe the equation is 12FeCl₂ + 3O₂ = 8FeCl₃ + 2Fe₂O₃, so you are right, some iron oxide is produced. But even so, the iron oxide can easily be filtered off, and not much product is lost, as much more ferric chloride is created that iron oxide.

I guess excess HCl will react with the iron III oxide produced to make ferric chloride and water via 6HCl + Fe₂O₃ = 2FeCl₃ + 3H₂O, thus increasing yield a bit.

And draconic's procedure in the last post is to get around the production of the iron oxide sludge, I assume.

[Edited on 4-11-2013 by blargish]

[Edited on 4-11-2013 by blargish]

Anomalous - 4-11-2013 at 12:23

Quote: Originally posted by blogfast25

Dissolve scrap iron in an excess 37 % HCl, filter off insolubles. Oxidise the FeCl2 solution with 35 % H2O2, slowly and with constant cooling.

Evaporate the FeCl3 solution, while maintaining an acid reserve to prevent hydrolysis. FeCl3 is very soluble and difficult to get to crystallise. It's all been explained somewhere on this forum. UTSF.

My interest is in keeping the FeCl3 in solution.

I did use the search engine, and did not find anything so helpful to me as the content of this thread. In fact, I've spent days working out the stoichiometry for various reaction paths, finding my mistakes, doing it over again, watching YouTube videos, reading articles, searching this forum and others. I reached the point that I felt it was sensible to ask a question and be involved with a community that knows better than I. While I may be new to this hobby, I don't need anyone to remind me to search. Thanks for your contribution, go on being superior and kindly avoid my threads.

To everyone else, thank you for your thoughtful contributions.

Anomalous - 4-11-2013 at 12:38

Quote: Originally posted by woelen

Nearly all sources of Fe2O3 sell calcined oxide. This is very inert and hardly dissolves in acid. It takes forever to dissolve even a small amount of this oxide in a large excess amount of acid. This method of making a solution of ferric chloride is not useful at all. Well before the acid is used up (even when still more than half of the acid is still remaining) the reaction comes to a near halt.

This is the spec from my supplier:

"Red Iron Oxide – Natural
Typical Analysis
Fe 5.5 %
Fe2O3 82 %
MgO 1.1 %
Mn 0.4 %
Al2O3 2.9 %
SiO2 8.0 %
Pb 30 ppm
As 20 ppm
Moisture 1 %"

From this can we make an assumption about calcination?

blogfast25 - 4-11-2013 at 13:44

Quote: Originally posted by Anomalous

[...] go on being superior and kindly avoid my threads.

Stop being childish. Stop trying to read minds: there's nothing in what I wrote that tries to convey superiority. They're not your threads: this is a public forum.

Quote: Originally posted by Anomalous

From this can we make an assumption about calcination?

No but most of us here have learned the hard way that commercial oxides are usually hard calcined and far more unresponsive to strong acids than some textbooks would have you believe.

[Edited on 4-11-2013 by blogfast25]

blogfast25 - 4-11-2013 at 14:16

Quote: Originally posted by blargish

I believe the equation is 12FeCl₂ + 3O₂ = 8FeCl₃ + 2Fe₂O₃, so you are right, some iron oxide is produced.

You can't just pretend there isn't any water present and hope for the best.

The oxidation half-reaction is:

Fe²⁺(aq) ===> Fe³⁺(aq) + e^-

The reduction half-reaction in neutral conditions:

O₂(g) + 2 H₂O(l) + 4 e^- ===> 4 OH^-(aq)

Then balance the electrons and add Cl^- to make both sides charge neutral. You end up with a mixture of FeCl₃(aq) and Fe(OH)₃(s). Freshly precipitated Fe(OH)₃ will readily dissolve in strong HCl though, so there needs to be no loss of iron. But air oxidation remains slow. Slight heating, good stirring and good dispersal (fine bubbles) of the air throughout the mix will of course speed things up.

blargish - 4-11-2013 at 15:37

Quote: Originally posted by blogfast25

Quote: Originally posted by blargish

I believe the equation is 12FeCl₂ + 3O₂ = 8FeCl₃ + 2Fe₂O₃, so you are right, some iron oxide is produced.

Gah, silly mistake by me. It is best to keep the solution acidic with excess HCl, as we get

4Fe²⁺(aq) + O₂(g) + 4H⁺(aq) = 4Fe³⁺(aq) + 2H₂O(l)
or
4FeCl₂(aq) + O₂(g) + 4HCl(aq) = 4FeCl₃(aq) + 2H₂O(l)

Thanks for clarifying

And Anomalous, are you making this ferric chloride solution for a PCB etchant?

Anomalous - 4-11-2013 at 19:33

Quote: Originally posted by blargish

And Anomalous, are you making this ferric chloride solution for a PCB etchant?

Yes, that was the plan.

[Edited on 5-11-2013 by Anomalous]

blargish - 5-11-2013 at 04:14

Ok, then

. I found these two videos on youtube, one of which details the inexpensive production of ferric chloride, whilst the other one goes over other PCB etchants that can be made with relatively cheap chemicals. However, the ferric chloride in the video is made via use of steel wool and HCl, so if you are bent on going the Fe₂O₃ route, I guess these will be of no help.

Make Ferric Chloride
http://www.youtube.com/watch?v=43Xsh9J7Sg

10 Other PCB etchants
http://www.youtube.com/watch?v=Q4tWEse2rDI

Sorry if you have seen these already

[Edited on 5-11-2013 by blargish]

Anomalous - 5-11-2013 at 07:09

I have seen these, thank you. The steel wool approach was attractive at first, until I realized how expensive steel wool is as compared to Fe2O3. That, and there is the added expense of an oxidizer or time spent bubbling air into the FeCl2 solution.

Fe2O3 seemed like a great option to me, as there is no intermediary FeCl2 as I understand it.

I've learned that calcined Fe2O3 is nearly non-reactive in solution, however. I wonder if performing the reaction in a pressure cooker might speed things along.

blogfast25 - 5-11-2013 at 13:54

Quote: Originally posted by Anomalous

I wonder if performing the reaction in a pressure cooker might speed things along.

It's possible but not very likely: domestic pressure cookers only increase temperature by about 20 C with respect to the standard BP of water, so not very much at all. And being made of steel (possibly also aluminium) they're very reactive to HCl and other strong acids. So unless you fancy a scalding blast of super hot 37 % HCl in your face when a microhole has finally been drilled through the pan, I wouldn't go there!

High pressure dissolution does of course work in principle and is used industrially in the refining of Bauxite (alumina mainly) by dissolving it in very strong NaOH in high pressure autoclaves. But there operating temperatures of 170 - 180 C (Wiki) are achieved, now that does speed things up a bit!