he said only have Pd so... in this case is better Zn. with DMG you dont have as a result the Pd metal, you have a intermediate Pd-DMG and then you have to liberate the Pd.
Precipitating palladium help needed
- Thread starter niels-chemist
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After checking Hokes book again, the Formic acid reduction should be done in a slightly acidic solution and at boiling temperatures.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 I sent you the important links we use yet?
niels-chemist
Active member
What is the best way to convert (DMG)2Pd into Pd(0)? I dont have and dont want to heat stuff to decomposition temperatures and I need palladium powder for my chemistry, not a palladium nugget. Would (DMG)2Pd dissolve in concentrated HCl so you can precipitate the Pd with formic acid afterwards?
niels-chemist
Active member
Not yet. The weird thing is: when I make Pd black I dissolve Pd in aqua regia, make it slightly alkaline and then add excess formic acid. This works really well and the solution becomes completely colorless with nice black powder sitting on the bottom. Then when I take small samples from my waste solutions and do the same thing, nothing happens.
Here are the links, including for Hokes book.
Her book is our goto book on refining.
We ask our new members to do 3 things.
1. Read C.M. Hokes book on refining jewelers scrap, it gives an easy introduction to the most important chemistry regarding refining.
It is free here on the forum: Screen Readable Copy of Hoke's Book
2. Then read the safety section of the forum: Safety
3. And then read about "Dealing with waste" in the forum: Dealing with Waste
Suggested reading: The Library
https://goldrefiningforum.com/threads/gold-refining-forum-rules.31182/
Her book is our goto book on refining.
We ask our new members to do 3 things.
1. Read C.M. Hokes book on refining jewelers scrap, it gives an easy introduction to the most important chemistry regarding refining.
It is free here on the forum: Screen Readable Copy of Hoke's Book
2. Then read the safety section of the forum: Safety
3. And then read about "Dealing with waste" in the forum: Dealing with Waste
Suggested reading: The Library
https://goldrefiningforum.com/threads/gold-refining-forum-rules.31182/
You can add HCl and Zinc powder during stirring, it also works fine.
Or even Al powders.
Or redissolve and use Formic on that.
No need to use AR, Nitric alone is fine with Pd.
niels-chemist
Active member
AR is quicker ;-) You can also use 37% HCl with 35% H2O2 ;-) Never tried it but according to the literature you can also use HCl and bubble O2 through the solution to oxidize the Pd.
kurtak
Well-known member
First having read this thread I understand that you are working with Pd solution that have no other metals dissolved - just the Pd
However - I do NOT recommend dissolving your DMG with any kind of alcohol & that is because if you should ever go to use DMG to precipitate Pd from a solution that also has silver dissolved in it you can inadvertently precipitate silver fulminate
Silver fulminate is highly explosive pressure sensitive explosive - so pressure sensitive that it can explode under its own weight as it precipitates from solution
There is a better way to prepare your DMG
100 ml hot water (does not need to be boiling - just "good" & hot)
Dissolve 4 grams NaOH in the water
Then dissolve 5.81 grams DMG in the NaOH/water
It takes 2.5 grams of DMG to precipitate 1 gram of Pd
The dry DMG/Pd precipitated salt will contain 31.67 % actual Pd
You can then reduce the DMG/Pd salt to Pd by way of calcination - chemical reduction (formic acid etc. etc.) or ion exchange using zinc powder & HCl
I prefer going with ether calcination of ion exchange as chemical reduction can be a bit tricky getting the chemistry just right
Edited to change word meals to metals in first sentence
Kurt
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niels-chemist
Active member
Thanks
I'm aware of silver fulminate. In the lab I work with serious stuff, but silver fulminate should be respected. Calcination is just heating it up to several hundred degrees C, right?kurtak
Well-known member
In an acidic solution & if you use ether zinc or copper powder (300 minus mesh) it happens VERY quickly
you need to keep the solution stirred when adding the zinc or copper powder so that the ultrafine zinc or copper meal particles make good contact with the dissolved Pd ions in the solution to get good ion exchange
There will be LOTS of foaming so leave plenty of head room in your beaker for the foam up
Kurt
niels-chemist
Active member
Thanks! What is the optimal pH?
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The formic acid process was strongly used to separate Silver and Palladium. It's an extremely interesting process to learn. Using it with AR seems counter intuitive but if you're sure it's working then I'm all ears.
niels-chemist
Active member
What I wanted to do is make palladium black (finely divided palladium powder) from palladium sheet. What I did is add the palladium sheet to an empty erlenmeyer, to which I added 36% HCl. After warming the solution I added small amounts of HNO3 until all Pd is in solution. I then let the solution cool and added 50% NaOH in water in small portions. Be careful as this gets very hot. When the solution is still hot, at around pH = 10 you get a large amount of brownish precipitate, which is palladium hydroxide. To this hot solution (I estimate around 70 - 80C) I added 85% formic acid in water. Be careful as it foams a lot. Immediately you get palladium black formed. To make sure you get everything precipitated I keep the solution warm for an hour or so and agitate it so the palladium sticks together in nice chunks that fall to the bottom. After that proces, the solution becomes crystal clear and completely colorless.
Neils, from your posts you ask questions like someone trained in chemistry. Yet you do not seem to grasp some basic principles. The suggestions you have received here are proven to be successful. To achieve your goals you will be best served by cementing the Palladium to give yourself a clean impure powder to refine and eventually drop as Palladium Black. Not understanding why zinc does not drop the precious metals as clean as copper does is puzzling to me, what you have had suggested to you is basic chemistry.
Try what has been suggested and you will have gotten off to a better start.
Good Luck
Try what has been suggested and you will have gotten off to a better start.
Good Luck
Instead of using O2, I use Ozone. it also works on Catalytic ceramics
niels-chemist
Active member
Not a bad idea, but best do it outside or in a fumehood. Any good oxidizer will come with risks for the human body.
niels-chemist
Active member
The Zn does not seem to disappear in some quick&dirty tests I did on tiny scale in a test vial. Monday I will do it again, but with lower pH and higher temp and more vigorous stirring.
The thing is: theory and practice don't always match. Maybe the Pd concentration is too low. Maybe the Pd was already precipitated and I mixed up solutions. Humans make mistakes. Maybe there is still HNO3 present that immediately oxidizes any Pd(0) back to Pd2+... Maybe my Zn has gone bad and is covered by an oxide layer.
Yes, I have a PhD in chemistry. Although it is basic theory, (best) practice can sometimes be based on practical experience. Not every chemist has experience in refining PGMs.
Fun fact: Zn can be Zn1+, but only with special ligands under strictly anhydrous conditions. There are always chemists trying to find new oxidation states for metals and during my PhD Au2+ was discovered and published. Cu2+ is easy. Silver being larger, is already more difficult to get into 2+ oxidation state. Au2+ is an obscurity
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kurtak
Well-known member
When I use the cementation process (ion exchange) - in acidic solutions Ph 0 - 1 --- which is what the Ph should be after dissolving the metals in the first place so no need to adjust Ph
In alkaline solutions (cyanide) Ph of at least 10.5 but it doesn't hurt to go higher
I just finished cementing Au from a cyanide solution with shredded aluminum foil to recover the gold still in solution after recover most of the gold in an electro winning process
In other words - I used electro winning to recover most of the gold from the cyanide solution (about 31.5 ozt gold) --- I then used cementation (with shredded aluminum foil) to "mop up" any remaining gold ions in the cyanide solution after electro winning & recovered another 2.25 ozt gold --- did that mop up (cementation) at Ph 13 - 14
I don't quite understand this - if you are dissolving the Pd in AR your Ph should already be 0 or 1 at most - so why are you needing to lower Ph - have you done something to raise Ph before cementing
if you are cementing from an AR solution the reaction should be very vigorous (especially if you are using zinc powder) & there should be no need to apply heat as it will generate it's own heat from the acid reacting with the zinc
Kurt
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Niels.
I'm a bit confused as to what you do.
First you dissolve the Pd in AR and then drop it as Hydroxides by lifting the pH to 10.
I fail to see the reasoning behind this.
If I'm not mistaken, the Formate reduction can be done without the Hydroxide conversion.
And then you start talking about cementing with Zinc, is this cementing an alternative to the Formate reduction?
When cementing with Zinc it is common to wash the resulting powders in weak HCl to dissolve any surplus Zinc.
Or one can cement it a tad to little and clean up the rest with either DMG or put it in a stock pot to scavenge the rest.
There is as Kurt says, almost always more than one way to skin a cat.
Calcining is prone to losses if it is done to fast or too hot in the beginning.
I'm a bit confused as to what you do.
First you dissolve the Pd in AR and then drop it as Hydroxides by lifting the pH to 10.
I fail to see the reasoning behind this.
If I'm not mistaken, the Formate reduction can be done without the Hydroxide conversion.
And then you start talking about cementing with Zinc, is this cementing an alternative to the Formate reduction?
When cementing with Zinc it is common to wash the resulting powders in weak HCl to dissolve any surplus Zinc.
Or one can cement it a tad to little and clean up the rest with either DMG or put it in a stock pot to scavenge the rest.
There is as Kurt says, almost always more than one way to skin a cat.
Calcining is prone to losses if it is done to fast or too hot in the beginning.
