# Pt precipitation



## turtlesteve (Sep 21, 2010)

Forum experts,

I tried precipitating a platinum solution with ammonium bicarbonate instead of ammonium chloride, thinking that the bicarbonate would react with HCl in the solution, and the end result would be the same. I did get most of the metal out as ammonium hexachloroplatinate, but the resulting solution is very deep red in color. A second sample of the same Pt solution precipitated with ammonium chloride does not give a red solution. Additions of HCl and ammonium chloride to the red solution do not result in precipitation of any type, but I can cement out the metal as a black powder. The red solution has pH = 3. 

The starting solution was made from Pt/Rh powder dissolved in HCl / H2O2, which was heated to remove excess H2O2. A portion of Rh remained undissolved, but some might have made it into solution.

What did I make? Is there any way to get the values to precipitate, or do I need to cement it and start over?

Steve


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## samuel-a (Sep 22, 2010)

I'v found that cementing PGM's from a solution containing ammonium is not such a good idea... the resolting black powder act as if liquid and stay in suspantion for a few days....

so i'll join your Q.


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## Lou (Sep 22, 2010)

Red solution is probably rhodium. H3RhCl6 looks blood red.


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## turtlesteve (Sep 22, 2010)

I cemented it, and yes, now I'm having to centrifuge at 7000 RPM to get the colloidal powder out of suspension. Won't do that again.

Also, I didn't think Rh would dissolve from the powder that much - I would like to separate the two if possible, how would I go about doing this?

Steve


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## Lino1406 (Sep 24, 2010)

You need to verify that some values were left there.
This I'd do by taking a sample, add some water
and putting a copper strip inside.
If positive, cement


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## Platdigger (Sep 24, 2010)

Could be time for a bisulfate fusion.


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