# Odd results with formate reduction



## samuel-a (Jan 9, 2013)

Hi all

I was given a mix of PGM's black, supposedly containing Pt, Pd and unknown but little amounts of Sn, Ni and maybe some Ti and Sb.

The mixture sample was boiled twice in dilute HNO3/d. water for couple of hours to remove Pd and Ni and form H2SnO3 and take up Sb if it's even there.

The nitric leach was filtered, then, two teaspoonful of NH4HCO2 was stirred in and the mixture was allowed to gain temp' on the hot plate.

Once hot, i've added slowly NaOH solution until the ink show up and pH stable at 3.5-4... after 20 minutes of boiling, all of the black powder clumped together real nice as shown below:



I haven't done this many times before but as far as i know, this should indicates reletivly clean Pd precipitation... Anyways, this powder was exteremly easy to wash as it settles very fast and there were no tiny floating paticulants, it was washed several times with boiling tap water, then with slightly acidified water and again with boiling d. water.

The black was later dried and weight for record. So far so good.

I have decided to heat it with a torch in a glazed porcelain crucible (heating the crucible from underneath to red hot) to ensure all moisture was indeed out as it formed several large and very rigid clumps (it was bone dry and this step was not needed). it was then allowed to cool back down.
What happened next was quite surprising, as i opened the crucible cover, i noticed the powder has turned to reddish/gray color... almost like dry copper powder looks like.

So the next step was to redissolve the Pd black in AR, starting first with just HCl and heat to dissolve PdO and then moving on and adding HNO3.
The result of the AR was even more suprising... Pd did went in solution, BUT i have now this maroon sludge now:



It is insoluable in hot water, HCl, nitric and AR.... Now, i'm going the long way of cementing what Pd that did went in solution with Al and then try again with NH4Cl + Cl.

The remaining maroon powder was washed well with water and HCl and will be dried later, i will try to calcine it and hopefully decompose what ever it is... and try leacing it again with nitric acid.


Your thoughts please...


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## Joeforbes (Jan 10, 2013)

It's Zirconium.

We refine catalytic converters, and end up with massive amounts of this brown paste (verified to be Zirconium with XRF). It will only dissolve in hydrofloric and sulfuric acid or hydrofloric and nitric acid. Depending on how it came off of the original source material, it can end up in a readily soluble charge state.

It's not too big of an issue, but you will want to heat the material in acid for quite a bit longer than you normally would to be sure that no PGM's are left in the sludge.


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## samuel-a (Jan 13, 2013)

Thank you for your reply Joe, much appreciated.

I'm a bit confused as to where Zr came from (the source material is not cat's), though i'm not ruling out anything.

After washing it several times with boiling hot water, I have calcined the powder and there was a distinct formation of PdO, as seen here:




Leacing again with HCl and then with AR resulted in a very colorful Pd solution and again more residues of the same maroon powder...

I guess my question is, if it is that insoluble, how come it entered the solution in the first nitric leach... ?


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## Lino1406 (Jan 14, 2013)

Ru is out of question?


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## Joeforbes (Jan 14, 2013)

There is of course a possibility of it not being Zr, but it definitely has all of the characteristics of it.

Depending on what the source material was, and how it was processed, the Zr can end up in a soluble charge state. 

In catalytic converters (which I know isn't the source of this material) I suspect that we produce zirconyl chloride which is readily soluble in water and would be precipitated by many other metals, including zinc. I'm not at liberty to discuss the process we use, it's proprietary and a very guarded secret of ours, but it's likely to be produced in a number of different manners. Zirconium compounds are very commonly used as thermo-barrier coatings, and some of these compounds are more reactive than others.

I wish I had more information for you on how it ended up in the material, but its chemistry is still a mystery to me for the most part. 

You should be able to have a near full recovery of the PGM's in the Zr sludge though (99.5%+) if Zr is in fact what is it. Just keep leaching until it doesn't leach any more, and try to keep it agitated as best as possible.


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## samuel-a (Jan 14, 2013)

Thanks Joe

Since we both no at liberty to discuss this further, i reckon i'll just keep burining/leaching the powder until it's over.
On the process scale i have no problem, It was the first time i tried to perform a quantitative analysis (for Pd and Pt) for this material with formate reduction.




Lino1406 said:


> Ru is out of question?


I don't think so... but given the colors, i guess it might.


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## Sucho (Jan 17, 2013)

samuel.

i think you produced hydrated palladium oxide, which is hardly soluble and gives this colour. 

as i realized time before with samples from formate reduction and further analysis via ICP-MS and some calculations, PdO is composed and due to water environment it is easily hydrated.

it will decompose only at high temperatures - cca 800 degrees for few hours


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## Lino1406 (Jan 22, 2013)

That is - ready for melting


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