Sciencemadness Discussion Board

Dissolving Ir and IrO2 to Hexachloroiridate

Osmiridium - 16-3-2023 at 17:00

Hi there!

I am looking for a way to dissolve Iridium and convert it to Hexachloroiridate.
The reaction of the metal with molten KOH/KNO3 forming IrO2 works pretty well and happens fast.
Now I also know it is possible to convert Ir and its oxide easily to Hexachloroiridate by mixing it with NaCl and heating it to high temperatures (at least 600°C) in a Cl2 atmosphrere. This seems to be a standard procedure.
I mean this might very well be feasible but it's a bit nasty and unpleasant with this chlorine at high temperatures. Also it would be necessary to obtain a special quartz or ceramic tube for that.

I wonder if somebody knows any easier way to accomplish it.
May be unlike metallic Ir IrO2 might be soluble in aqua regia or in some mixture like KNO3/HCl? In any case Ir is not soluble in these. Since it is so expensive I don't want to mess around with it too much trying different things.

Many thanks in advance for any useful information and suggestions!

Σldritch - 17-3-2023 at 06:21

I am trying to learn how to dissolve, separate and refine the PG-metals myself. My plan so far is to use hydrochloric acid and anodic oxidation. Perhaps this could work for you too? Maybe I am missing something obvious. Also, if you know a good resource on the subject I would be happy to know of it.

DraconicAcid - 17-3-2023 at 08:21

I've only worked with iridium in its lower oxidation states, but I'd imagine that the oxide would be much more reactive towards acids than the free metal, since you wouldn't need to oxidize it further.

Osmiridium - 17-3-2023 at 17:31

Quote: Originally posted by Σldritch  
I am trying to learn how to dissolve, separate and refine the PG-metals myself. My plan so far is to use hydrochloric acid and anodic oxidation. Perhaps this could work for you too? Maybe I am missing something obvious. Also, if you know a good resource on the subject I would be happy to know of it.


Anodic oxidation sounds interesting, but my material is more a coarse powder/granules making this difficult.
Most information I have is from the scarce resources I found on the internet that cited references I don't really have access to and from books like "Inorganic Chemistry" by Hollemann Wiberg.
But there is also the "Handbook of Preparative Inorganic Chemistry" by Georg Brauer. Section 29 in volume two of the second edition starting at page 1560 is about the platinum metals. The original is in German and there is an English translation too. The latter is actually available in the Sciencemadness library! The German version is also available somewhere in the net.
Quote: Originally posted by DraconicAcid  
I've only worked with iridium in its lower oxidation states, but I'd imagine that the oxide would be much more reactive towards acids than the free metal, since you wouldn't need to oxidize it further.


Yes, exactly. I also thought this might be the case. Although from what I read the platinum group oxides are generally also quite inert.

Anyway, so far I managed to get rid of some of the impurities by oxidizing with KOH/KNO3 and washing with some hydrochloric acid. I obtained a very heavy grey powder that does not go into solution with the acid along with some insoluble white impurities stemming most likely from the ceramic crucible.
I think I'll just try to treat it with aqua regia and observe what happens. If anything happens at all. :)

[Edited on 18-3-2023 by Osmiridium]

[Edited on 18-3-2023 by Osmiridium]

Bedlasky - 17-3-2023 at 23:42

Try dissolve IrO2 in aqua regia, it is done industrialy during isolation of iridium. If it won't work, try dissolve it in molten anhydrous NaHSO4 or KHSO4.

Rhodium metal dissolve in molten NaHSO4. Iridium doesn't, but maybe if some oxidant like KNO3 is present, maybe it force iridium to dissolve in melt??? (HSO4- as complexing agent, NO3- as oxidizing agent)

Iridium is insoluble in aqua regia. I know that rhodium can be dissolved in aqua regia at 200 °C, but I don't know if this is possible with iridium.

http://www.ajchem-a.com/article_92164_e9bc6183bdc619dec8940a...

[Edited on 18-3-2023 by Bedlasky]

fusso - 18-3-2023 at 00:27

How even could AR exist at 200C?!:o

[Edited on 230318 by fusso]

Rainwater - 18-3-2023 at 03:09

https://www.semanticscholar.org/paper/The-chemistry-of-ruthe...
Attachment: The Chemistry of Ruthenium, Rhodium, Palladium, Osmium, Iridium and Platinum.pdf (5MB)
This file has been downloaded 359 times

Page 15 has a table which might be helpful.
But does use high heat in some steps.
Good luck.
It is very hard to refine and the industry is
tight lipped about how its done professionally.

[Edited on 18-3-2023 by Rainwater]

DraconicAcid - 18-3-2023 at 08:28

Obviously, if you don't know how to get your iridium to react the way you want, you shouldn't be entrusted with it. You should send it to me for safe keeping.


(Disclaimer: obvious joke is obvious.)

Osmiridium - 19-3-2023 at 04:25

Quote: Originally posted by Bedlasky  
Try dissolve IrO2 in aqua regia, it is done industrialy during isolation of iridium. If it won't work, try dissolve it in molten anhydrous NaHSO4 or KHSO4.

Rhodium metal dissolve in molten NaHSO4. Iridium doesn't, but maybe if some oxidant like KNO3 is present, maybe it force iridium to dissolve in melt??? (HSO4- as complexing agent, NO3- as oxidizing agent)

Iridium is insoluble in aqua regia. I know that rhodium can be dissolved in aqua regia at 200 °C, but I don't know if this is possible with iridium.

http://www.ajchem-a.com/article_92164_e9bc6183bdc619dec8940a...


Unfortunately I doubt that hydrogensulfate will work with Iridium since this is usually described as a process to dissolve Rhodium and even separate it from Iridium.
Quote: Originally posted by Rainwater  
https://www.semanticscholar.org/paper/The-chemistry-of-ruthe...

Page 15 has a table which might be helpful.
But does use high heat in some steps.
Good luck.
It is very hard to refine and the industry is
tight lipped about how its done professionally.



Thank you so much for this. This indicates that IrO2 must be soluble in aqua regia! I had no time to try it yet but I certainly will do it soon. It's a very valuable piece of literature.
Quote: Originally posted by DraconicAcid  
Obviously, if you don't know how to get your iridium to react the way you want, you shouldn't be entrusted with it. You should send it to me for safe keeping.


:D

Osmiridium - 24-3-2023 at 08:10

In the last few days i conducted some experiments and I'm glad to share the results: Iridium dioxide is soluble in aqua regia and dissolves well!

I made an experiment with about 100mg of pure iridium powder. First the iridium was dissolved by pouring it in a molten 4:1 mixture of KOH/KNO3 in a small ceramic crucible (I didn't weigh the salts precisely as it shouldn't be that important if it's just enough but not too much). As I already wrote before, the reaction is smooth, fast and with the powder it did not take longer than a minute. The cooled down very dark bluish black residue was then dissolved in water and some remaining residue was scratched out of the crucible and all was transferred into a beaker. Some of the oxide was left on the walls of the crucible.

Now with the isolation of the oxide there's a little problem. Some of the oxide formed is extremely fine. So fine that it forms a colloidal solution with dark bluish almost black color. Even after passing it three times through the same filter it remained dark blue. The residue was then washed with water and dried over night.

Aqua regia was prepared in a 100 ml conical flask by mixing 5 ml 65% HNO3 with 20 ml of 33% HCl and to reduce losses the filter paper cut into strips was added to it. Then the mixture was put on a hot plate with about 100°C and left standing there for about 3h (the dissolution was certainly already finished after a shorter time).

It's important to note that heated aqua regia produces very nasty, corrosive and toxic fumes. It's necessary to do this in a fume hood or even better outside!

At first the mixture had a similar color like the colloidal filtrate and then gradually changed to a very dark wine red or almost brown.
Once the time passed it was let to cool down to ambient temperature and filtered through a paper filter to get rid of the residual paper fibers in it yielding a very dark red clear solution. The residue in the filter was rinsed with a few ml of water.

That's how far I got right now. The next steps will be the preparation of ammonium hexachloroiridate. And I still need to find a way to recover the colloidal IrO2 somehow and I want to dissolve the residual oxide from the walls of the crucible with aqua regia. No settling of the colloid could be observed even after few days standing. I will let it standing to evaporate a bit and then try to centrifuge it.



[Edited on 24-3-2023 by Osmiridium]

[Edited on 24-3-2023 by Osmiridium]

Rainwater - 24-3-2023 at 11:24

If you make nitric acid via the KNO3 + H2SO4 method, the byproduct KHSO4 can be used.
By heating it above 300c, but below 600c it forms K2S2O7, and can complex with Ir above 400c
Heating it above 600c will release so3 i think. Its nasty stuff and will ruin your equipment

From my refining, this is the only practical method for dealing with that metal.
Just 3% in gold and the melting point up to almost 1500c 5% and i can forget it. My oven wont touch it.

Theres suggestion on selective precipitation and a paper reguarding the process ....
https://goldrefiningforum.com/threads/dissolving-rhodium-wit...

Electrolysis is the only method ive tried to get a pure sample of the metal, havent got it to work yet. That stuff is hard not to sell, even in the oxide form. Good luck and stay safe

Edit:
I guess that link is old and i cant find my copy of the paper.
This may be helpful
Sciencemadness library Handbook of Preparative Inorganic Chemistry starting on page 1637 of the pdf( Page 1590 of the book)

[Edited on 24-3-2023 by Rainwater]

Fantasma4500 - 27-3-2023 at 05:28

NOCl? maybe some chlorine oxide species? bromine? but yes iridium is extremely annoying, i remember something about chlorine on that, was it maybe even liquid chlorine? very annoying indeed

if we assume that it simply just needs a lot of chlorine to react with, such as manganate where you need molten NaOH- very high OH level
could one maybe create a gas burner using hydrogen and chlorine, and then add in excess chlorine gas and blast the iridium with so that its blasted with superhot chlorine gas? quite theoretical.

Texium - 27-3-2023 at 05:44

Fantasma, please stop posting vague and ridiculous ideas for problems that have already been answered. I swear it seems like you read the title of a thread and vomit out a post without actually reading any of the previous posts.