Problem with DMG-palladium precipitation

[Mosana]

Hi everybody
I obtained an alkaline fused melt of rock suspected to involve palladium so, I dissolved the melt in hydrochloric acid, took 1 L of the resulted solution, diluted it with water and adjusted the pH with sodium bicarbonate, then added prepared DMG solution. There was no obvious yellow precipitate so continued adding sodium bicarbonate until pH of nearly 1.5. The only change was a cloudy like matter. This was left for a week without any daily investigation. After this time, about 2 cm height of white precipitate at the bottom of 1000 ml beaker was observed which on heating, first turned yellow, then brick-brown shiny powder.
Is this the Pd-DMG precipitate, which turned white due to impurities? Or other thing?
Thanks in advance

 

[etack]

Your not dissolving Pd with just HCl.

The metal in solution is not Pd If it was put into solution with just HCl.

Eric

 

[Mosana]

Neither Pd nor Pt does dissolve in HCl, but when you fuse your mineral rock which includes Pt or Pd, with an alkali like NaOH or Na2CO3, then you will obtain Pt and Pd as Na2Pto3 and Na2PdO3 which are easily dissolved in HCl especially in hot.
It has been found that trace amounts of Pd about 5 ppm can be precipitated by DMG as a voluminous substance and cause I know about Pd existence in my solution (based on AAS analysis) so, Pd SHOULD be precipitated by DMG but what is this WHITE precipitate?
Please answer, if you have experiences with DMG.
Thanks Eric.

 

[Lino1406]

The white precipitate is DMG not Pd(DMG)2

 

[Mosana]

I am not sure about DMG since a shiny brown powder was left after heating the white precipitate and evolving of white fumes. Have you ever calcined DMG powder to gain such a brown substance??

 

[Lino1406]

What keeps you from trying it yourself?

 

[Mosana]

DMG is completely converted to white fumes on heating. Very simple.

 

[Lino1406]

Then it is DMG mixed with some carbonate. Assuming pH was 5.1?

 

[Mosana]

No. pH was about 1.5. I did not apply more than 3 table spoons of bicarbonate.
I am sure there is anything else in white ppt.

 

[Lino1406]

You can't get this pH with bicarbonate

 

[Mosana]

If you dilute your solution with 5-6 times water and then add three tbs bicarbonate, exactly you will reach pH 1.5., you can try it for yourself, but my problem is not how to adjust pH!

 

[Mosana]

I have another acidic solution containing 20 ppm platinum and 3 ppm palladium (based on AAS analysis) and before adding DMG to it, I added some sodium bicarbonate and continued adding until changing color of the solution and just appearing of a brick-brown precipitate while pH was around 4. Then I decanted the supernatant and upon adding hot dimethylglyoxime solution, color of the solution from orange rapidly turned dark brown but without evident precipitate but a little greenish-brown powder was appeared. Considering the fact that DMG is selective for Ni, Pd and Pt (if solution is hot ) then, may the resulted powder be platinum?
Any comment is appreciated.

 

[butcher]

Nickel from acidic solutions?

 

[Lino1406]

Palladium DMG optimal pH = 4
Nickel optimal pH = 8

 

[Mosana]

butcher
I said platinum, not nickel as nickel DMG is almost red in color and my powder is greenish-brown (majority green).
Today I tried to dissolve this powder in HCl+H2O2 but the tinny amount was dissolved and the majority remained undissolved.
I am confused about it!