# Conversion of NH4 platinate to soluble form



## orvi (May 18, 2022)

Hi

I have a general question, probably for more experienced forum members.
I know that ammonium hexachloroplatinate is converted to the Pt sponge by incineration. Also, I know that (NH4)PtCl6 can be redissolved with AR (as sreetips done it in his video). 
Are there any other methods how to get the platinum back into the solution without the need of incineration+AR dissolution or using straight AR ? My intention is the second refining of ammonium Pt salt. So I need to get it back to the solution somehow. And if the de-noxing stage could be avoided somehow, I would be very happy.

Adding NaOH to the solution will probably produce unfilterable messy oxohydroxides of Pt. Maybe if it was done very slowly and in controlled way... But I do not feel comfortable with this.
Second thing that came to my mind was to use sodium bicarbonate in solution. This is much weaker base. Maybe in rolling boil conditions, evaporation loss of ammonia will be quicker than ripping off the chlorides from the PGM atom. Or using two equivalents of NaHCO3 create some undissolvable chloro-hydroxide Pt mess that could not be converted back to soluble form. Theoretically, with heating, ammonia will evaporate and hydroxychlorocomplex could be restored to the soluble form by adding just HCl. But I have no experience with this and maybe I am completely wrong.

I would be happy if you can share your experience on this toppic.

Thank you


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## nickvc (May 18, 2022)

Orvi as you know I’m no expert with PGMs but if you want to dissolve your powder simple water will do it I believe but I’m not sure if that helps with your needs .


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## orvi (May 18, 2022)

Solubility is about 5g/L in water at room temperature. 33g/L at boiling point. Not very much to work with, but I get another idea when reading your comment  My intention is re-purification of the platinate. I know it´s done by two step sequence of incineration or AR dissolution followed by second precipitation.


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## Lou (May 19, 2022)

I can dissolve it in sodium sulfite solution at pH 3- 5.

Then I can bring pH to 7-8, decant off the worthless supernate of ammonium chloride.

Redissolve precipitate in HCl, boiling to remove SO2. Add in hydrogen peroxide, HCl, boil to turn back into chloroplatinic acid. Precipitate again. 

Hydrolysis really only needed for Pt purification if other PGMs are present...


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## zachy (May 26, 2022)

Lou said:


> Puedo disolverlo en solución de sulfito de sodio a pH 3-5.
> 
> Entonces puedo llevar el pH a 7-8, decantar el supernato sin valor del cloruro de amonio.
> 
> ...


En esta etapa puede ser que sea donde se elimine el iridio, que se ha endurecido por la acción de la calcinación del exacloroplatinato de amonio, y para la segunda disolución no se calcina la esponja amarilla, mejor como dice Lou, hacer redissolución con sulfito de sodio e iridio permanecerá tan insoluble o como cloruro de iridio y quedará atrapado en el filtro. No estoy seguro de esta conclusión.


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## orvi (May 26, 2022)

Thank you very much sir.

So many possibilities with these metals  I was constantly thinking of exchanging ammonium cation for sodium whilst boiling away NH3 as gas from solution... But that is a crap idea.
Never think of it as this. To reduce platinum to make it soluble  octahedron vs. sqare planar. Now it makes sense to me


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## Lou (May 26, 2022)

zachy said:


> En esta etapa puede ser que sea donde se elimine el iridio, que se ha endurecido por la acción de la calcinación del exacloroplatinato de amonio, y para la segunda disolución no se calcina la esponja amarilla, mejor como dice Lou, hacer redissolución con sulfito de sodio e iridio permanecerá tan insoluble o como cloruro de iridio y quedará atrapado en el filtro. No estoy seguro de esta conclusión.


Unfortunately, it's not this easy. Ir removal from Pt requires a very high ORP in solution and slow pH rise. 

To remove Ir effectively, several treatments with NaOCl/Na2CO3 a la Gilchrist hydrolysis are often required. 

Ir and Pt (and Pd) form these sulfito complexes that behave the same. I will say that Ir/Ru sulfATE much more stable than Pd/Pt sulfate...if that gives you any ideas.

Alas, much that I would share is much that I've figured out the past 18 or so years of messing with these elements...for my sole source of income.


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