Precipitating palladium help needed

[niels-chemist]

I'm a chemist that does some palladium chemistry (in a professional lab). I collected and combined the waste from several (failed) experiments to precipitate the Pd2+ as Pd black. I also need Pd black for some experiments, which I could very effectively and quickly precipitate by dissolving Pd in aqua regia, then adding NaOH to make it alkaline (around pH 9 - 10) and subsequently, formic acid. This works well.

For unknown reasons I haven't succeeded in precipitating Pd(0) from my waste solutions. They contain a bunch of sodium salts (from adding sodium carbonate and hydroxide). I'm certain there is a bunch of palladium in there. When I take small samples from the solution and make it acidic with HCl you get the typicl PdCl2 color that changes to red-brown upon addition of NaoH (from Pd(OH)2). If I add formic acid to this solution and heat it up, nothing precipiates. I also tried adding SnCl2 (the redox reaction should give Sn(IV) and Pd(0), FeCl2 (which should give more stable Fe3+ and Pd(0)). In addition, I also used NaBH4, which definitely reduces Pd2+ to Pd(0).

I then tried to precipitate PdI2 and played around a bit with the pH after addition of excess NaI. Only from a small sample from the solution I managed to get black PdI2 solids precipitated. I do manage to oxide I- to I2 though, probably from some dilute, residual HNO3.

What am I doing wrong here? Shouldn't PdI2 precipitation be almost guaranteed because it's totally insoluble in water? I'm considering to order some DMG and add that as a solution in methanol or ethanol. If it works: does (DMG)2Pd dissolve in concentrated HCl? I think that would be the easiest to make alkaline and add formic acid for Pd(0) precipitation?

Suggestions welcome

 

[Yggdrasil]

I'm a chemist that does some palladium chemistry (in a professional lab). I collected and combined the waste from several (failed) experiments to precipitate the Pd2+ as Pd black. I also need Pd black for some experiments, which I could very effectively and quickly precipitate by dissolving Pd in aqua regia, then adding NaOH to make it alkaline (around pH 9 - 10) and subsequently, formic acid. This works well.

For unknown reasons I haven't succeeded in precipitating Pd(0) from my waste solutions. They contain a bunch of sodium salts (from adding sodium carbonate and hydroxide). I'm certain there is a bunch of palladium in there. When I take small samples from the solution and make it acidic with HCl you get the typicl PdCl2 color that changes to red-brown upon addition of NaoH (from Pd(OH)2). If I add formic acid to this solution and heat it up, nothing precipiates. I also tried adding SnCl2 (the redox reaction should give Sn(IV) and Pd(0), FeCl2 (which should give more stable Fe3+ and Pd(0)). In addition, I also used NaBH4, which definitely reduces Pd2+ to Pd(0).

I then tried to precipitate PdI2 and played around a bit with the pH after addition of excess NaI. Only from a small sample from the solution I managed to get black PdI2 solids precipitated. I do manage to oxide I- to I2 though, probably from some dilute, residual HNO3.

What am I doing wrong here? Shouldn't PdI2 precipitation be almost guaranteed because it's totally insoluble in water? I'm considering to order some DMG and add that as a solution in methanol or ethanol. If it works: does (DMG)2Pd dissolve in concentrated HCl? I think that would be the easiest to make alkaline and add formic acid for Pd(0) precipitation?

Suggestions welcome

Have you tested with Stannous Chloride or DMG?

 

[4metals]

Welcome to the forum.

Did you cement your failed experiments on copper to isolate the precious metals in the solution from whatever chemical liquors you were working with? This would give you a cleaner solution to start with.

 

[niels-chemist]

Have you tested with Stannous Chloride or DMG?

DMG not because I dont have it in the lab yet, but I have tested stannous chloride (SnCl2) and it doesn't seem to do anything. Yet from the same solution I manage to get a black precipitate upon addition of sodium iodide. This black precipitate is palladium(II) iodide, so there must be palladium in there....

 

[niels-chemist]

Welcome to the forum.

Did you cement your failed experiments on copper to isolate the precious metals in the solution from whatever chemical liquors you were working with? This would give you a cleaner solution to start with.

Not sure what you mean by that but I doubt it is necessary. The only things in solution are a large amount of sodium chloride (from making the solutions acidic with HCl and alkaline with NaOH, Pd2+ ions and some purely organic stuff. There are no other PGMs present because I already started with 99.95% pure palladium.

 

[100tific]

you can fall down your Pd using copper powder. it is call cementing. Pd ions are reducing to Pd and Cu is oxided to Cu ions. It is need to use Cu in powder because if you use a piece of Cu it will be covered of Pd and it will not react more.

 

[niels-chemist]

you can fall down your Pd using copper powder. it is call cementing. Pd ions are reducing to Pd and Cu is oxided to Cu ions. It is need to use Cu in powder because if you use a piece of Cu it will be covered of Pd and it will not react more.

Why not use zinc? It is far cheaper and easier to oxidize...
Or aluminum?

 

[100tific]

i tried to fall down Pd using a solution of KI 10% in the past. First you have to eliminate all the nitric acid. Then you have to heat your main solution, and when it is hot, add the solution os Ki 10%. it have to be slowly because if you use more than need the precipitate of PdI2 could redissolve. you will note that it produce purple gases of I2. When no more precipitate form, (difficult to see) Let it temper and filter the black precipitate of PdI2.

 

[100tific]

¿Por qué no utilizar zinc? Es mucho más barato y más fácil de oxidar...
¿O aluminio?

If you are sure that your solution only have Pd, you can use Zn without any problem. If you have more metals, using copper you garantice only precious metals fall down

 

[niels-chemist]

If you are sure that your solution only have Pd, you can use Zn without any problem. If you have more metals, using copper you garantice only precious metals fall down

There is sodium in there, but if you can precipitate sodium metal from water using zinc you will have a Nobel price lol

I started with 99.95% pure Pd and did not use any other noble metals. What pH is optimal for adding Zn powder? Does it work between pH 6 and 9? If too acidic or alkaline the zinc will react to ZnCl2 or Zn(OH)2...

 

[100tific]

i always work in acid medium. zinc will form ZnCl2 and Pd go out of PdCl2

 

[niels-chemist]

i always work in acid medium. zinc will form ZnCl2 and Pd go out of PdCl2

but if Zn is converted into ZnCl2 by H+ (with formation H2) it can no longer do redox with Pd2+?

 

[100tific]

w you put Zn there, Zn is oxided and Pd is reduced. If you put Zn in HCl, Zn is oxided and H+ is reduced.

 

[Yggdrasil]

but if Zn is converted into ZnCl2 by H+ (with formation H2) it can no longer do redox with Pd2+?

Since cementation works well both in Acidic and Alkaline solution.
It used to be the goto solution to drop Gold from Cyanidation.
Cementation is a "simple" ion exchange operation.

 

[niels-chemist]

Since cementation works well both in Acidic and Alkaline solution.
It used to be the goto solution to drop Gold from Cyanidation.
Cementation is a "simple" ion exchange operation.

Thanks. I would say that it works at room temperature and needs some stirring time? How quick is it?

 

[100tific]

Dado que la cementación funciona bien tanto en solución ácida como alcalina.
Solía ser la solución ideal para eliminar el oro de la cianuración.
La cementación es una operación de intercambio iónico "simple".

yes it is true, it works in alkaline solution too, i forget cianide solutions.

 

[Yggdrasil]

Thanks. I would say that it works at room temperature and needs some stirring time? How quick is it?

I have never used it, so I can't say.

 

[niels-chemist]

I have never used it, so I can't say.

How about DMG? Is that always guaranteed to work?

 

[100tific]

yes, stirring, it not take so much time. Try it in a little recipe and then scale it.
with DMG you have to do a lot of steps. it works but with zn is more easy and quickly.

Thanks. I would say that it works at room temperature and needs some stirring time? How quick is it?

 

[Yggdrasil]

How about DMG? Is that always guaranteed to work?

The most important difference is that Zn is not selective but DMG is.
It is usually considered impractical due to price and volume of precipitate.