Kadriver writes:
I have had this beaker sitting on one of my shelves for months containing Palladium dissolved in nitric acid. The palladium came from mixed black PGMs, I extracted the Pd using dilute nitric acid, then evaporated it to remove most of the liquid. I did a stannous test and it is loaded with palladium, the standard test solution on the left contains 100mg Pd dissolved in 100ml liquid.
The brown stain on the left corresponds to the reference-solution, containing 1g Pd/liter. The stain on the right shows clearly, that Pd and Pt are present. The Pd-concentration in the sample-solution seems to be much higher, than 1 g Pd/liter. The Pt-concentration, as indicated by the strong orange coloration of the paper, concentric around the dark-green Pd-stain, seems to be quite high, too. One can distinguish between Pd and Pt by washing the stains on/in the paper with copious amounts of distilled water. The Pd-stain (dark green) will disappear slowly, being washed out completely, whereas the orange Pt-stain will stay back on/in the paper.
RaoOvious writes:
Make sure that there is no trace of nitric acid(water washes and Ph neutral) before washing the Pd black with dilute HCl,otherwise some of the Pd black would again go into the solution.
In my practice, this was never a problem. In contrary, a too low electrolyte/acid-concentration can lead to peptization of such PGM-blacks, making their filtration more and more cumbersome. Assuming a rest-wash-solution-pH of 2 for the last filtration step, and a volume of 5 ml liquid means, that a maximum-amount of 5*10-5 moles HNO3 is available, to oxidize a maximal amount of 5*10-5 gram-atoms Pd-metal to Pd(II), corresponding to a maximal possible loss of 5.3 mg Pd, in an experiment like presented here, by Kadriver.
@Greyish solution after cementation and intensive washing of Pd:
This greyish colour/turbidity may well be caused by small amounts of residual, unreacted zinc-powder, reacting slowly with water to very small particles of insoluble zinc-hydroxide, Zn(OH)2. Thus it is not necessary, to filter. Chance is, that this turbidity disappears on addition of some diluted acid.
@Kadriver:
As I can see from your last posts, you're on a very good way. First, dissolving residual zinc with diluted HCl, followed by filtering, washing, drying. This leaves you with a weighable amount of raw Pd-powder, and you know now much better, what you are working with.
You already have dissolved the Pd-black in HCl/H2O2, which should leave you with a solution containing mainly Pd(II), together with some Pd(IV).
Contrary to you, I am not surprised, to see how much Pt you are precipitating. SnCl2-testing to me shows clearly the presence of quite a lot dissolved platinum.
In order to clarify my comments I have collected some of your fotos in the attached pdf-file.