# Reducing agents for PGMs



## orvi (Yesterday at 1:54 PM)

Hi
I combined my personal knowledge with all I could find on the Internet but I still have a feeling that I didn´t covered it all. My main focus is now on PGMs and palladium in particular.

We all know classic cementations with base metals such zinc, aluminium, iron or copper. Work OK, but always leave residues of that metal in the precipitate, sometimes are tricky or incomplete (PGMs on copper), or rather precipitate nearly everything (iron, zinc...). Plus leave more waste in solution, which is not nice.

Then, there are inorganic reducing agents such as borohydride and hydrazine. Effective, but borohydride for PGMs is not that great, leaving many times very fine suspensions of flammable metal powders. Hydrazine is great, but hard to get (here) and hazardous - toxic and explosive.

And finally, organic reducing agents - for use in PGMs reduction mainly pronounced formic and ascorbic acid. I found formic acid to work well, altough somewhat slow - but whatever. Ascorbic acid is quicker, but vast ammounts are needed eg in processing palladium from nitrate solutions, and it also have tendency to drag copper.
I am currently in the middle of refining one stubborn material - leach from MLCCs. It is now in the stage where it has Pd as major component, alongside copper, nickel and residues of tin. Vast majority of tin, lead and barium were removed prior. I did not make it, but I accepted that I will help with the refining to the Pd button.
Problem with this feed is - it contain quite a bit of solubilized junk from ceramics (and possibly some tin residues, as tin is amphoteric). So anytime I want to approach it by some organic precipitants (which I am used to use), I need to raise the pH. Precipitate of this junk always appears - filtering is OK, I filter it crystal clear, and proceed. But then as reduction start, this junk will almost everytime appear again, creating myriad of nucleation sites and causing precipitation of ultrafine, contamined palladium powder - nightmare to deal with. Currently, due to tin/lead and barium removal step it is in nitric/nitrate enviroment (first formic acid precipitation was from nitric).

Ascorbic and formic acid by their very nature need at least low acidic pH to become reducing agents. But there is certainly more reducing agents in class of organic compounds or inorganic compounds that will reduce precious metals. 
My question is, how the reduction could be done without raising the pH ? Is there any reducing agent that will work in acidic solutions for precipitation of say palladium, other than ones I mentioned ? DMG is my last resort - I know that it will save the day if it comes to palladium  but DMG has it´s own problems, could be done of course, altough I feel it is unnecessary to use it here 

I thought about formaldehyde, as it has stronger reducing power than formic acid. 

Any input would be greatly appreciated 

Thanks
orvi


----------



## Platz (Yesterday at 5:59 PM)

Bubbling carbon monoxide or hydrogen through would work if the palladium was present as a salt. Not sure if it would if it is in solution. But you could probablly drop the palladium as ammonium chloropalladate at high acid with a good selectivity over tin, filter it then reduce it with either of those gases or burn it. Make sure you have a good hood and gas monitor if you try this.


----------



## orvi (Today at 3:43 AM)

Platz said:


> Bubbling carbon monoxide or hydrogen through would work if the palladium was present as a salt. Not sure if it would if it is in solution. But you could probablly drop the palladium as ammonium chloropalladate at high acid with a good selectivity over tin, filter it then reduce it with either of those gases or burn it. Make sure you have a good hood and gas monitor if you try this.


I have access to hydrogen cylinder, so maybe this will be viable method. If I get it correctly, I drop the palladium salt, filter it, suspend in water or so - and bubble hydrogen through ? Is pH critical during this transformation ?
How badly palladium powder obtained by this method burn in the air (there would be good ammount of hydrogen adsorbed) ?
Thank you for the suggestions


----------



## lazersteve (Today at 8:42 AM)

Search for papers written around 1868 by Bunsen on the topic of separation of PGMs. He details the use of molten zinc as a recovery/collection method from raw ores followed by hydrogen gas reduction.
This is the same Bunsen that the famous "Bunsen Burner" is named from. Frankly I'm surprised I haven't seen his work mentioned more on the forum.

Steve


----------



## kurtak (Today at 12:20 PM)

lazersteve said:


> Search for papers written around 1868 by Bunsen on the topic of separation of PGMs. He details the use of molten zinc as a recovery/collection method from raw ores followed by hydrogen gas reduction.
> This is the same Bunsen that the famous "Bunsen Burner" is named from. Frankly I'm surprised I haven't seen his work mentioned more on the forum.
> 
> Steve


Hi Steve & thanks for chiming in

I did a search using - "separation of pgms from ore by bunsen " - but did not find any papers by Bunsen

Could you provide a link ?

Kurt


----------



## Lou (Today at 12:28 PM)

orvi said:


> I have access to hydrogen cylinder, so maybe this will be viable method. If I get it correctly, I drop the palladium salt, filter it, suspend in water or so - and bubble hydrogen through ? Is pH critical during this transformation ?
> How badly palladium powder obtained by this method burn in the air (there would be good ammount of hydrogen adsorbed) ?
> Thank you for the suggestions


This is your easiest route to pure ish Pd.

At a few atmospheres H2 at room temp is pretty selective for Pd over all other elements.

60 psi at room temperature will give you Pd. It is best if it is not highly acidic.

Pd, Pt, Rh, Ag, Ru, Ir in that order of ease to reduce from solution with hydrogen. Ir is practically impossible


----------



## lazersteve (Today at 1:08 PM)

Search for "On Rhodium" +Bunsen + 1868

If you can't find it, I will dig you up a copy. I believe the original version is not in English (German if my memory is correct ).
The translation was missing the drawings, but the original isn't. 

Steve


----------



## butcher (48 minutes ago)

Robert Bunsen german He has several chemistry books written in the German language. online book stores carry them.


----------



## lazersteve (17 minutes ago)

This is a letter/article and is titled "On Rhodium", it is 3-5 pages long depending on which version you get.

Steve


----------



## butcher (5 minutes ago)

Kirchhoff Gustav Robert Wilhelm Bunsen - AbeBooks


Chemische Analyse durch Spectralbeobachtungen," in "Annalen der Physik und Chemie." ++This is a great classic, a foundation paper in the history of spectrum analysis.++ by Kirchhoff, Gustav and Robert Wilhelm Bunsen. and a great selection of related books, art and collectibles available now at...



www.abebooks.com














Robert Bunsen


Author of Gesammelte Abhandlungen Von Robert Bunsen, Anleitung zur Analyse der Aschen& Mineralwasser, and M�thodes Gazom�triques...



www.goodreads.com


----------

