Mixed Black PGM Powders

[samuel-a]

Hi Steve


The Pd salt i'm referring to is not the red hexachloropalladate. But the yellow Palladosammine salt which has a subsentually lower decomp' point (and lower solubility).

It was all done in the solution, where the salt is in its solid state. So no cloud was produced. The water cooled condenser returns all vapoers back to the beaker.

All in all, the process was pretty neat.

Sounds like you basically calcined the salt from the solution.

Yes, i think so too. The undissolved salt decomposed due to the solution temp'.

I hope i could reproduce this process (when i get more Pd) with the same results and share it here.

 

[lazersteve]

The Pd salt i'm referring to is not the red hexachloropalladate. But the yellow Palladosammine salt which has a subsentually lower decomp' point (and lower solubility).

Sam,

I believe the two salts, the yellow and the red are the same salt:

'palladosammine chloride' (I believe you left off the chloride part by mistake)

according to Hoke pg 284:

...The residue contains the platinum, gold, and the rest of the palladium in a form particularly suitable for extraction with aqua regia,which is the next operation. From the solution of chlorides thus obtained, the gold is precipitated as brown gold by means of ferrous sulphate, and then the platinum as ammonium chloroplatinate by the addition of ammonium chloride, and lastly, the palladium is precipitated as palladosammine chloride. The only one of these operations which calls for special comment is the precipitation of palladosammine chloride. The palladium present as chloride is converted into soluble tetrammino-palladous chloride by the addition of excess ammonia solution according to the equation:

PdCl2+ 4NH3 = [Pd(NH3)4]Cl2

When excess of hydrochloric acid is added, the sparingly soluble yellow compound known as palladosammine chloride is precipitated according to the equation:

[Pd(NH3)4]Cl2 + 2HCl = [Pd(NH3)2Cl2] + 2NH4Cl

Notice she declares the name of the palladium salt as the same name before it is purified with ammonium hydroxide and after.

Perhaps I'm reading the passages wrong, but it seems to read that the Palladium is precipitated, then purified as the same salt.

Regardless of whether they are the same salt or not, they are easy enough to convert back to Pd sponge via reduction or heating.

Steve

 

[samuel-a]

I believe the two salts, the yellow and the red are the same salt:

As far as i can tell, the are not.

This is getting quite confusing though. From what i know:
Yellow powder, Palldosammine Chloride - Pd(NH3)2Cl2 is a coordination compound where Pd is at +2
Red powder, Ammonium Hexachloropalladate - (NH4)2PdCl6 is a simple ammonium salt where Pd is at +4

Beside that, from my personal experience, they don't look the same and don't behave the same. So my only conclusion would be that they are not the same.


I'm sure Lou could help us set things stright with the proper terminology.

 

[samuel-a]

Upon firther reading, i can see the confusion now. I think you do missed something in the text Steve.

She calls for:
After addition of NH4Cl to precipitate Pt, she say to add ammonia (to produce soluble tetrammine complex, +4) and then re-acidify with HCl to precipitate a diammine yellow salt.
Just as you would re-refine you red powder. (Dissolve red powder with ammonia and precipitate with HCl)

The red powder precipitate when you oxidize ammonium tetrachloropalladate (+2) (PdCl2 + NH4Cl) to ammonium hexachloropalladate (+4) (tetrachloro + Cl).


I hope i got all the numbers right.... my eyes are getting heavy...

 

[kadriver]

The liquid did not settle and it was still very dark so I added some more ammonium chloride, added heat and stir.

It looks like more brick red powder came down.

I'll filter tomorrow and gather all the powder together.

kadriver

 

[lazersteve]

Sam,

I agree they appear different and behave slightly differently, but either way the end result is the colored powder is reduced to the metal by any one of several means.

Hoke's wording is very confusing indeed especially with her naming of the colored salt. Adding ammonium chloride to denoxxed solutions does not precipitate red Pd salt until the chlorine oxidizer is added.

Platinum salts commonly change colors (from green, orange, and yellow) as they are precipitated and purified further.

Steve

 

[Lou]

You've got the names right Sam; both are different and have different crystal structures (the diammine is octahedral and will wash better).


I'll pull an ounce of the diamminepalladium (II) chloride and try this "wet calcination" by setting it up for reflux in a 1 L with saturated ammonium chloride solution. If I like it, I'll try it on production lot and we will publish a communication to the Platinum Metals Review AFTER we check to see if it's been mentioned. Is this something you came up with on purpose or just by serendipity? Grain size is very important to me. How things rinse is CRITICAL to purity and easy handling.


Steve,

I agree that it is most confusing. The nomenclature back then wasn't really well defined with many things having common names or names of convenience. There was no really systematic method until IUPAC (which is hell on earth for complex molecules!!!!).

 

[samuel-a]

That was by chance Lou

I have noticed that when i was trying to wash yellow salt with boiling NH4Cl solution (1 mole) , the color went slightly darker upon gentle boiling.
From that, i deduced that decomp' must have occured and i knew the decop' temp' is quite low for yellow Pd. Some of it dissolved.

So the next trial was to boil as hard a i can, under reflux with saturated NH4Cl.
After 3 hours, The majority (i reckon about 95-98%) of the black powder clumped up ino tiny spheres that settled fast, the rest was as cloud of black powder that took several hours to settle.
I have noticed only very slight coloration of the solution from dissolution.

---------------------------------------
I'm very ashamed for not keeping better lab records, but that just the way i am...

I hope you could repeat the process with sucsess. I'm sure that with your knowledge, you could fine tune it far better then i ever could.


Edit: i will also try this with Pd-DMG.

 

[lazersteve]

I did a little digging in my CRC Handbook of Chemistry and Physics 55th Edition and found that the colorless, tetragonal palladium salt (tetra-ammine palladium (II) chloride Pd(NH3)4Cl2.H2O) decomposes at 120C when heated.

The palladium salt ( Pd(NH3)2.Cl2 ) dichlorodiammine palladium II trans or alpha) decomposes at an unspecified temperature when heated and appears as yellow tetragonal crystals.

PdCl2 has a decomposition temperature as 500C.

Do you recall what temperature the reaction occured at?

Steve

 

[samuel-a]

Yes Steve

At around 120-130C (reading from hotplate, not the solution it self), decomposition became noticeable.

I later ramped up the heat all the way up and left it alone. about two hours later there was no more signs of yellow. I kept it boiling for one more hour just to make sure.

 

[RaoOvious]

Kad keep ur visual sequential going....

 

[kadriver]

I filtered the powder from the last re-heating operation.

It yielded quite a bit of additional brick red powder.

I added this to the rest of the powder from the other filterings into a 600ml beaker and set up to add ammonium hydroxide.

 

[kadriver]

I did not know what kind of reaction to expect since this is my first time doing this.

When I opened the bottle of ammonia, the filter with a little of the damp red powder on it began to emit a white fume!

I added about 20ml of the 29% ammonium hydroxide and poured a small amount into 600ml beaker with the palladium brick red powder.

Then I stood back, because of the fumes, and watched the reaction.

 

[kadriver]

The reaction subsided quickly, so I added more ammonium hydroxide and stirred as per the instructions.

The flesh colored precipitate formed immediately and I stirred while adding more ammonia.

I quit stirring for a few minutes and the precipitate settled quickly to the bottom of the beaker.

I added more ammonia and looked for signs that the flesh colored precipitate was dissolving in the ammonia.

I kept adding ammonia and stirring, but the precipitate was not dissolving so I put it a the stir plate with no heat.

 

[kadriver]

I let it stir for about 30 minutes, then turned the stir plate off.

The precipitate began to settle out quickly so I added more ammonia.

I could not see where the flesh colored precipitate was dissolving.

I put it back on stirring and that is where I am at right now.

I have added about 300ml of the cold concentrated ammonia so far.

More to follow.

kadriver

 

[Lou]

It will dissolve, you may need to heat it.


The white fumes are ammonium chloride produced from residual HCl in your ammonium hexachloropalladate.



Lou

 

[kadriver]

Thanks Lou, I added a little more ammonia and put it on to stir with a little heat.

I noticed the beaker that holds my glass stir rod had a nice yellow crystal looking powder form that looked like the powder I am trying to make here.

I don't know if this yellow powder in the stir rod beaker is the right stuff or not.

I stopped the stir for about 5 minutes and allowed everything to settle just to get a bearing.

Then I added a few more ml of ammonia and placed on low heat and stir.

The color of the precipitate looks almost like Bazooka Joe Bubble gum.

I'll keep heating and adding ammonia until the precipitate dissolves completely.

kadriver

 

[freechemist]

Seeing this topic to grow enormously into a big discussion, centering mainly on aqueous Pd-chemistry, I can not refrain from adding some comments from my own experience with palladium recovery/refining.

The biggest difference between what is stated in Hokes book about precipitation of (NH₄)₂PdCl₆, ammonium-hexachloropalladate(IV), and the experiments done by kadriver, is the fact, that Hoke refers to Pd, mainly dissolved in an excess of aqueous HCl (originating from AR, used to dissolve), whereas kadriver starts with a more or less concentrated nitric acid solution, supposedly not containing any chloride. In Hokes case chloro-complexes of Pd, mainly PdCl₄^2-, are already present, and thus, Pd(II) is easily oxidized with chlorate/HCl, to Pd(IV), forming finally the complex anion PdCl₆^2-, which can be precipitated as red, sparingly soluble (NH₄)₂PdCl₆ by addition of an ammonium salt, preferrably ammonium chloride.

In kadrivers case chloro-complexes of Pd have first to be formed, what apparently is done by addition of NH₄Cl. In order to precipitate (NH₄)₂PdCl₆ at least 4 moles of NH₄Cl are used up to form the complex anion PdCl₄^2-, and at least two moles more chloride are used, to form Cl₂, to oxidize Pd(II) to Pd(IV), leading to the complex anion PdCl₆^2-. Nitric acid alone is a weaker acid as HCl, and is also a stronger oxidant in presence of another, stronger acid, like HCl in AR. Thus, oxidation of Pd(II) to Pd(IV) gets easyier in presence of an excess of HCl.

In the discussion the danger of explosive NCl₃-formation on use of NH₄Cl and NaClO₃ is mentioned. This can easily be overcome by using KCl in place of NH₄Cl. In my hands K₂PdCl₆ has never been much more soluble than (NH₄)₂PdCl₆, so I recommend to use KCl in further experiments.

Dissolution of metallic palladium in nitric acid or mixtures of sulfuric/nitric acid is not a simple reaction as it looks like, leading to solutions of PdSO₄ and/or Pd(NO₃)₂. Reduction-products of HNO₃ remain bound to Pd(II) tenaceously, even on prolonged, strong heating. This can well be seen by dissolving Pd-sponge/black in 62% sulfuric acid by adding only a small excess of nitric acid, in order to oxidize Pd(0) to Pd(II), where only small amounts of brown NO_x are formed. Adding such Pd-solutions to refluxing aqueous HCl leads to final evolution of copious amounts of brown fumes, forming the known solutions of H₂PdCl₄.

 

[Lou]

KCl is great for Pt and Pd both because a large excess can be added to suppress the solubility without fear of causing a huge headache in waste treatment like ammonium chloride.

We will not use it in our processes because we calcine our salts and KCl is exceedingly difficult to remove from them. It also hazes the quartz reduction equipment by causing devitrification.

If you use hydrazine or formate, go for it.


I've never made NCl3 (unintentionally) during palladium precipitation. It will not form at the low pH of 2+ M HCl solutions.

 

[kadriver]

As you can see, I added more ammonia and heat on the stir plate.

This precipitate does not seem to want to go into solution - so far I have added nearly 400ml of 29% ammonia.

I placed the beaker on my deck with a plastic bucket and cinder block on top for the evening.

Tomorrow I will continue trying to get the flesh colored (more like bubble gum) precipitate to dissolve.

Is it possible I have dissolved all that can be dissolved?