# Purification of ammonium hexachloroplatinate



## tensor9 (May 14, 2012)

Hi everyone,

I work in a research lab, so I have to work on the cheap and recover platinum that I use for catalysis. I recovered the platinum the usual way via the ammonium hexachloroplatinate route. However, somewhere along the way I got some foreign matter in it that may be impractical to remove manually. Given its low solubility in water, this might turn out to be a little bit of a pain. Granted, its solubility in pure water is appreciable (3.365 g/100 g H2O @ 100 °C). I would be all for dissolving it in boiling water and hot filtering it, but i'm a little worried about hydrolysis. Perhaps do it in dilute HCl?

Any help would be appreciated.


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## lazersteve (May 14, 2012)

Convert it to the sponge (zinc + acid, hydrazine + base, etc.), dissolve in AR, filter, and precipitate again.

Steve


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## HAuCl4 (May 15, 2012)

It depends what "foreign matter" you got it mixed with. Base metals?. Salts?. Plastic?. Dirt?. Glass?. Clay?. Other PGM powders or salts?. Radioactive stuff?. Explosive stuff?. etc?. Any useful answer will depend on that.


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## tensor9 (May 15, 2012)

I'm not exactly sure, but it's probably dirt, aluminum oxide/iron oxide from a corroded clamp. In other words, I'm fairly confident the foreign matter isn't easily soluble in water or dilute acid. The preferred method would be to just hot filter a solution of the hexachloroplatinate. If it really came down to it, I could basically take everything back up in aqua regia (hope the contaminants dissolve, or not), evaporate, redissolve, filter, then reprecipitate with ammonium chloride, but I do not want to go through all that. Was hoping about some info on recrystallization.

I'm using this to make Adam's catalyst (heating the hexachloroplatinate in molten sodium nitrate to yield PtO2 hydrate), so I would like to get rid of any metal contaminants.


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## HAuCl4 (May 15, 2012)

Lou is probably your man to get a proper answer re. your final aim of Adam's catalyst. It sounds like one could make an explosion if not careful. (At least all the pieces are there). :shock: 

For recrystallization purification a better salt is K2PtCl6, which is way more soluble in water and less dangerous.

I don't think this helps you much. Good luck.


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## freechemist (May 18, 2012)

Hi tensor9,

It is possible to purify ammonium and/or potassium hexachloroplatinates through some sort of "chemical-reaction-recrystallization", like mentioned in the European Patent Nr. EP0537133B1.

In a series of chemical reactions the only sparingly soluble hexachloroplatinate is transformed first into a much better soluble Pt-compound, whoses solution may be filtered, and after filtration be further treated in an appropriate second chemical reaction, to reform and reprecipitate the original hexachloro-compound. According to the cited patent (examples given only in German; claims are in English, too) (NH4)2PtCl6 is transformed into (NH4)2PtBr6, one time without, and a second time with addition of small amount of a reductant, able to reduce some of the Pt(IV) to Pt(II). Apparently addition of a small quantity of reductant leads not only to a better yield, but also to higher purity of the product.

Theoretically you could reduce your (NH4)2PtCl6 to much better soluble (NH4)2PtCl4 with a stoichiometric amount of reductant, filter the solution, and reprecipitate (NH4)2PtCl6 by reoxidizing Pt(II) to Pt(IV). However, quantitative and selective reduction of Pt(IV) to Pt(II) is not as easy, as it looks like, because simultaneous formation of some metallic platinum is quite frequently encountered. I am sure, that there exist appropriate combinations of redox and/or ligand-exchange-reactions, to purify hexachloroplatinates efficiently, without necessity to reduce the salt to the metal and rebeginning by dissolution of the metal in AR. Obviously such a successful procedure is neither published, nor protected by a patent, because every patent means also to publish the patented procedure. 

Good luck, freechemist


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## tensor9 (May 21, 2012)

Still seems like a huge pain in the butt. I'll play with it and see what happens. If push comes to shove, I can start over.

Thanks!

I'm putting readers on notice. I do not accept the use of less than polite language on this forum. I am going to start deleting posts that don't comply, having taken note that my cautionary message is being ignored. 

http://goldrefiningforum.com/phpBB3/viewtopic.php?f=33&t=14035

Harold
Edit on 6-20-12 -to clarify that the word above "butt" is the word that was substituted by me in lieu of allowing a more vulgar term to remain on the board. To my knowledge, the use of the word butt is acceptable in polite society, as opposed to the more vulgar term that was replaced.


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## Palladium (May 21, 2012)

You will not get a better man to answer your question than freechemist. Unless of course it's Lou. They are at the top of the food chain when it comes to this kind of stuff.


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## lazersteve (May 21, 2012)

tensor9 said:


> Still seems like a huge pain in the butt. I'll play with it and see what happens. If push comes to shove, I can start over.
> 
> Thanks!



I wish PGM chemistry were easier to deal with myself, but you play with the cards you are dealt. 

I learned a long time ago that if this was easy, everyone would be doing it. So many people think there is a magic bullet for everything. I've found hard work and preserverence are the keys to success. It pays to do things the right way, you may just find your shortcut (if you find one) actually results in more effort.

Reducing the salt and redissolving the resulting powder for a second precipitation can be accomplished in a very short time if you know what you are doing. Knowing comes from doing.

The fastest route would be to use hydrazine and ammonium hydroxide to reduce the salt. I prefer the zinc-acid route because I'm trying to keep ammonia out of my processes these days. Both of these processes work on just about any scale and are proven to get the job done.

Here's a few photos of a 40+ ounce batch of Pt I purified for a customer about a year ago:

The dirty Pt powder the customer brought to me (looks black but is actually drab green):







This is one of the final precipitations of the above material after using the zinc acid method:







Steve


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## tensor9 (May 22, 2012)

It seems as if the recrystallization in dilute HCl worked just fine. So, for any who already have marginally pure ammonium hexachloroplatinate, keep it in mind. The powder looks a BIT more orangish than I would like. Maybe I can take a pick when I get it filtered and see what you all think.


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## Lou (May 22, 2012)

Alternatively, you could indeed oxidize the ammonium cation component in hot aqua regia back to chloroplatinic acid; unless it is very hot and very concentrated, you're better to do as Steve says. Depending on the situation, I will reduce with excess zinc and redissolve in aqua regia and go hydrolytically or go directly with the ammonium hexachloroplatinate and proceed the same.

Dilute hot HCl will also work. You can add sat'd ammonium chloride as needed to drive down the solubility. Done right, your filtrate should be clear with no yellow color and a faint stannous.


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## freechemist (May 30, 2012)

Patent Application "*Offenlegungsschrift DE 199 28 027 A1*" from Heraeus GmbH in Germany gives another procedure:
K2PtCl6, dissolved in water at 75 C is passed slowly through a column, filled with a cation-exchange-resin (strong acid). Thus the K+-ions are retained by the resin and replaced with H+-ions. The pure, metal-free H2PtCl6-solution is then reduced to very pure Pt-metal.



Sorry, I have a copy of the original document only in German.



Regards, freechemist


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## western_1 (Aug 28, 2012)

HAuCl4 said:


> Lou is probably your man to get a proper answer re. your final aim of Adam's catalyst. It sounds like one could make an explosion if not careful. (At least all the pieces are there). :shock:



hello, 
I plan to make some PtO2 myself. would you please elaborate the dangers of this process?
Concerning the first step, the preparation of H2PtCl6;
The reaction of aqua regia with platinum is planned. Platinum and nitric acid were obtained and 
the reaction mechanism goes like this :
HNO3 + 3 HCl -> NOCl + 2 Cl (nasc.) + 2 H2O
Now in one database, the platinum MSDS entry says that NOCl reacts with platinum explosive if heated. 
1) my understanding is, Pt is only going into solution if heated. Is it THAT dangerous ?
2) also, will the platinum catalyse the evolution of Cl und NOCl so if scaling up it would generate too much heat and vapours?
3) up to what scale is it possible to produce aqua regia alone without generating too much vapours ? 
4) how can one calculate the generated heat ? i suppose the beginning is endothermic (because it has to be heated) and the reaction itself is exothermic?
5) would it be possible to dissolve even 1kg of platinum in 10L of aqua regia or is this too dangerous because of the generated heat?
6) is it necessary to use aqua regia as a solvent, so that more than the stociometric amounts of HCl has to be used?

thanks for any suggestions!
should i open a new thread or is this ok here?
kind regards,


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## Lou (Aug 28, 2012)

It's better to dissolve 1 kg of platinum in about 5 L of aqua regia. 

We use 6M in HCl and HNO3 as there is not much rate advantage above that and less efficiency due to offgassing. 

I think if you have to ask these questions, you should not attempt to make or use PtO2.

If you have a 1 kg of Pt to dissolve, I will trade you that same amount of PtO2 
I have some fresh and ready to go.


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## western_1 (Aug 28, 2012)

please correct me if I am wrong ; 

Pt
(195,08 g/mol)
(5,126102 mol/kg)

assuming that the reaction goes to completion 
HNO3 + 3 HCl -> NOCl + 2 Cl (nasc.) + 2 H2O
and every mol of Pt needs 6 mols of Cl (nasc.), one would need thrice this amount of the proposed reaction.

the concentrations of the available acids are:
HNO3 (70% ; 15,8mol/L)
HCl (36,2% ; 11,89mol/L)

5,126102 mol * 3 = 15,378306mol == 0,973 L HNO3 (70% ; 15,8mol/L)
5,126102 mol * 9 = 46,134918mol == 3,880 L HCl (36,2% ; 11,89mol/L)

What is not accounted for is:
-the needed solubility of the reactants in the reaction flask, 
-the, due to time, changed concentration of acids,
-the escaped and escaping reactants (HCl, Cl2, NOCl, HNO3)
so one should use more HCl to start with.

So far, I have read that goldsilverpro has proposed the 2-step-AR-procedure, which is what I was looking for. Mixing the Pt in Hcl (aq.) and slowly dripping in HNO3. He proposed it for gold but it could work for Pt, although slower, nevertheless, right ? 
Do I remember correctly that the temperature shouldnt exceed 80°C during the reaction and evaporation? Do I understand correctly that you use 6M solution of AR or do you use 6M Pt to begin with ?
thanks for your response

Is there something I am missing ?


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## western_1 (Aug 28, 2012)

Lou, I cannot write a PM to you. Appears I am too new to write a PM to an OP or at all?
Would you please contact me about: "If you have a 1 kg of Pt to dissolve, I will trade you that same amount of PtO2 "
If I send you a PM, the message, "No recipient defined." comes up over and over, although I have included you in the recepient.


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## Palladium (Aug 28, 2012)

He will see it and pm you.


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## Lou (Aug 28, 2012)

Yes, I'll send you a PM.

I do this for a living. If you need Adam's catalyst, that's no problem. Most simple PGM salts/compounds we keep in stock here. I don't know if I have enough PtO2 offhand to cover it.



And for the record, unless your Pt is in black or sponge form, or heavily diluted with other base metals (we use copper), it's going nowhere fast. 

We put it in 100 L flask and chlorinate it into solution.


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## western_1 (Aug 28, 2012)

I got your message, but i cannot reply. it still keeps telling me "No recipient defined." could you check you settings, if I am not allowed to write PM or would you please send me an email adress via PM ? kind regards


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## tensor9 (Sep 13, 2012)

western_1,


I would recommend you use ammonium hexachloroplatinate, as opposed to hexachloroplatinic acid, as a starting material for making Admam's catalyst. The MAIN difference in synthesis is that you add concentrated ammonium chloride to the hexachloroplatinic acid solution. Ammonoium hexachloroplatinate is also very much a more convenient starting material because it is not extremely hydroscopic like the acid and can be reliably stored and weighed. People here can give you lots of detail on how to do this. Do you have access to a fume hood?

As for the PtO2, it's actually not that difficult to make if you have the right equipment. If you have a large furnace with reliable temperature control that goes to ~550 C in a WELL ventilated fume hood and a porcelain dish, you're most of the way there. My lab has only tube furnaces, so I use quartz tubes for the reaction (pyrex cracks too easily at theses temps). I can go into detail about the synthesis if you'd like.

Also, one tip for whenever you actually make PtO2. Upon completion of the reaction, it's easiest to poor the molten mixture directly into a stirred, large container of water. You have to exercise great care because the melt is at 500 C, but it makes the workup of the PtO2 much, much faster and less tedious. 

Anyway, if you have an specific questions, let me know. Also, I suppose a good question question to ask is: how experience are you in the laboratory? If you're not experience, I wouldn't recommend you attempt this.


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## Lou (Sep 13, 2012)

I think he has it handled now.


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## HAuCl4 (Sep 14, 2012)

Lou said:


> I think he has it handled now.


Hi Lou. I spoke to a knowledgeable russian chemist this week and he told me, amongst other things, that the relatively low price of rhodium is being affected by all the nuclear waste re-processing that is already going on, on an industrial scale. Apparently someone has found a way to economically extract the non radioactive precious metals that are by-products of the fission reactors. Apparently enough time has passed already and there are lots of waste from old nuclear plants that can be safely processed after this time lapse.

What do you think?.


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