# Selective dissolution of Pd



## tensor9 (Jun 21, 2012)

I stumbled upon a method of separating Pd from Pt using 35% nitric/[stt]37% HCl (1:2)[/stt] [Edit: no HCl is needed. Only 35% nitric). This is supposed to selectively dissolve Pd. I did a cursory search on the forums but found no mention of it. If this has been discussed before, I apologize.

Any thoughts?


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## Lou (Jun 21, 2012)

From what is it supposed to separate Pd from? It won't separate it from Pt or Au.


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## Westerngs (Jun 21, 2012)

Post the method.


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## tensor9 (Jun 22, 2012)

The method, roughly goes like this. Actually, looking at it more closely, the HCl is not necessary for the dissolution, sorry.

From Fleaker on Sciencemadness,




> Your failure was improper removal of free chlorine from the solution. Also, you will not get Pt (VI)!
> 
> 1.) Take all of your values containing solutions and reduce them by adding zinc. pH should be between 2-3.
> 2.) Remove excess zinc by rinsing the cemented metals with 3M HCl until no more fizzing, then boiling water.
> ...


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## jimdoc (Jun 22, 2012)

That is funny, knowing who Fleaker is. 8) 

Jim


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## Lou (Jun 22, 2012)

I think you are misquoting the poor guy as this isn't a new method--all it says is that you can separate the Pd and Ag with nitric acid; he then goes on to discuss that one should make the solution more rich in chloride anion to make chloropalladic acid, and to ensure it is all oxidized. 

Reading the fellow's post, this method is meant to give higher quality platinum by getting rid of palladium, silver, and other base metal traces early on in the procedure. Then the platinum is present only with other PGMs (sans Pd) and perhaps nonmetallics (i.e. SiO2)


Aside from nitric acid and sulfuric acid, there are no selective practical solvents for Pd.


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## tensor9 (Jun 22, 2012)

Re-read my post. I already corrected myself that the HCl isn't necessary.(It's essentially to separate the Ag and to provide Cl for the chloropalladate.) And in no way did I suggest that it is a new method but was asking if it is a possible alternative method. I'll edit the mistake from the original to avoid confusion.

The point stands. Can you use 35% nitric to dissolve Pd away from Pt? And to be precise, as you pointed out, how much Pd will this get rid of? This post was a reply to another post, and there was no indication that this was to rid the mixture of traces of Pd but rather bulk Pd.


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## lazersteve (Jun 22, 2012)

Tensor,

Have you seen this thread?:

Separating Mixed PGM powders

Steve


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## tensor9 (Jun 22, 2012)

lasersteve,

Perfect! Thanks (Lou). 

I suppose my main concern is leaching Pt out while dissolving the Pd, so the least likely reagent to do this is desirable. Hence, the question about he 35% nitric. When I recover Pt, it's usually in the from of Pt black, so the particles are almost in the nanometer regime. I know Pt is a rock, but things become much more reactive with such high surface areas.

This also helps answer another question I had about Rh/Pt separation. A friend gave me some used Pt, Pd, and Rh and/or Ir electrodes a while back, so I just digested them all up in AR (except the Rh/Ir of course). I was not particularly careful in making sure no Pd or Rh contaminated my Pt salt precipitates. It's possible that some Pd has hitched a ride with my Pt--as my ammonium HCP salts have an orange tint to them (but the catalyst has been working anyway). I've had a small batch of filtrate from the electrode digestion that obviously contains Pt for quite a while, so I figured I'd add some concentrated ammonium chloride to crash out the remaining PtCl62-, but in the process some green precipitate formed as well. I assumed the Rh wire would not dissolve at all in boiling AR, but it appears that a Rh salt is a possible source of the green. So, thanks Lou! 

On a related note, I have a Rh/Pt solution from a HBr/H2O2 digestion that I have to figure out how to handle. But I will post in the relevant thread to see if you guys can help me out a bit or point me in the right direction. I suppose I have a direction in mind now..


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## Lou (Jun 22, 2012)

You're very welcome. I am glad that my information is useful to you.

You can remove the rhodium contaminant by boiling the solution (it should be between 30-45 g/L [PtIV] ) and adding small amounts of sodium bromate (which will form bromine in situ and keep the Pt and all other metals in their highest oxidation states where they form the most easily rinsed hydroxides) slowly neutralizing to pH 7.4-7.5 with sodium (bi)carbonate. Then you can filter out the junk. The rhodium will start leaving the solution at pH 4 as a lemon yellow fluff (sometimes it can be brown yellow).


Good luck.


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## tensor9 (Jun 26, 2012)

Will the amount of rhodium affect the separation? It turns out the solution is mostly Rh (Rh 4: Pt 1), roughly. (For the HBr dissolved Rh/Pt.)


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## Lou (Jun 26, 2012)

Yes. Rhodium is a persistent contaminant.


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## freechemist (Jun 26, 2012)

> *tensor9:*I stumbled upon a method of separating Pd from Pt using 35% nitric/37% HCl (1:2) [Edit: no HCl is needed. Only 35% nitric). This is supposed to selectively dissolve Pd. I did a cursory search on the forums but found no mention of it. If this has been discussed before, I apologize.
> 
> Any thoughts?



Yes, - a lot of thoughts, indeed. - How are the rare earths and your special chelating agents for them doing? - And, - what are you *really* running after? 

I always enjoy to read your posts and your clearly formulated questions. So, I think, you really ask/look for a method to dissolve Pd selectively from metallic PM-residues of origin unknown to me. Nearly 20 years ago I , myself was confronted probably with a similar, if not the same problem. I had to refine metallic Pd-residues containing 80-90% Pd, about 10% Au and a small amount of Pt, without affecting gold and, if possible, platinum. It took me a lot of lab work (which, besides, I liked much) until I found an easily reproducible and well running procedure, to refine this raw Pd up to a quality of 999.9%oPd.- Provided with some more significant information from your side, maybe, that I can give you some hints.

freechemist


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## tensor9 (Jun 27, 2012)

I'm after single molecule magnets. I can go on and on, but it turns out lanthanides have great single ion anisotropy (Tb, Dy, Ho, and Er especially) and high spins, so they are currently being explored as an alternative to transition metal single molecule magnets. (None of the known SMM are worth much, though, since they loose their hysteresis properties at less than 10 K or so.) The idea is to eventually make a room temperature single molecule magnet for use in data storage and quantum computing.

I've attached a pic of the cluster.


As far as the precious metals go, I'm mainly trying to get rid of Pd, if any, so that it doesn't contaminate my Pt catalyst. The amount of Pd present is probably negligible (my catalyst still works fine), but I am just curious for future purposes.


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