# PtPd nitrate solution trouble with hydrolysis



## orvi (Jun 28, 2022)

Hi
from refining of various leftover solutions, we found one canister of relatively clean PtPd solution in nitric acid (apparently from leaching some material). There are no chlorides in solution, just nitric with some few % of dissolved iron and nickel, aside of PtPd. 

No big deal, around 10-15g in 10 L. So we assumed, we can neutralize HNO3 with hydroxide to pH around 8, to precipitate palladium as hydroxide. We known that this procedure do not produce best filtering ppt, and also it was disclosed only for denoxed chloride solutions.

After *raising the pH to 8,* quite a bunch of ppt appeared, which after filtration shown all base metals (expected) and Pd with only trace Pt. XRF of the solution shown no Pd, so we happily assumed that all Pd is out. 
After obtaining *clear Pt liquid, we intended to raise pH to 12 and more to precipitate it* from the solution, but there some strange observations happened. *No matter what ammount of 20% KOH I added to the sample, no precipitate appeared in the liquid, even after few hours. *
Why is that ? Does some strange nitrito/hydroxo-complexes form and stay dissolved ? Or it was just because low concentration ? (around 1g/L Pt)

Next we proceeded to cementation of the leftover Pt liquor with aluminium. Aluminium was chosen because there was essentially only Pt in the reading and in basic conditions, Al salts would be soluble, allowing to filter the solution, in opposition with much more common copper or iron cementations.
So I raised the pH to 13 with KOH and sticked aluminium wire to the solution. It proceeded nicely, altough somewhat slower than I expected. Afte like 5 hours of bubbling and ton of ammonia produced, solution completely lost colour and no dark precipitate formed. 

*After filtering, we shot the resulting cemented Pt with XRF only to find that it is around 50:50 PtPd*... 
So we actually separated nothing, complicated the thing even further and found two "mysteries" on the way 

Can someone explain these observations ?


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## Lou (Jun 30, 2022)

Pt and to lesser extent Pd are soluble in excess alkali. 

Platinum on long boing forms some insoluble sodium hexahydroxyplatinate salts. Palladium probably does something similar. We see Pd in strong alkali all the time.


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