dissolving palladium in nitric acid

[Inter Refiner]

Hello,
I had some palladium powder that I recovered previously and refined. I dissolved the pd powder in nitric acid while heating, then I cemented it with zinc. After that I redissolved the cemented pd in nitric acid again while heating, but this time I have some red powder precipitated at the bottom, I am not sure what that is and why did form. I suppose that all the palladium must be dissolved as they were dissolved before in nitric.I use 68% nitric acid.



thank you

 

[FrugalRefiner]

I had some palladium powder that I recovered previously and refined. I dissolved the pd powder in nitric acid while heating, then I cemented it with zinc.

Not trying to be rude, but what was your objective in using zinc to cement the palladium? It would likely also cement almost anything else that had dissolved.

After that I redissolved the cemented pd in nitric acid again while heating, but this time I have some red powder precipitated at the bottom, I am not sure what that is and why did form.

My experience with PGMs is limited, but my guess would be that perhaps some of the palladium oxidized in your process, and I don't believe palladium oxides are soluble in nitric. I could be wrong.

Dave

 

[Lou]

The red powder is PdCl2, which isn't well soluble in nitric acid.

 

[Inter Refiner]

But where did the chlorine come from?!

 

[Lou]

I guessed you cemented from chloride solution. Cemented Pd powders hold onto lots of Cl-.

You can try dissolving the powder in excess ammonia or heating in c HCl to be sure.