Palladium precipitation by formic acid
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If done right, quality will be comparable or even better than that DMG dropped Pd. pH control is key for clean precipitation. Too high pH and copper alongside with other base metals can co-precipitate from the solution as oxohydroxides or other hydrolyzed species.
As i read the ph should be around 4 before dropping the palladium with formic acid, am i correct ?
pH4 is actually on the higher side. Between 2-4 is the optimum range, from every protocol I can find.
The scientific papers on the process I read suggested as high a purity as 99.7% was possible when reduction conditions were well-controlled and optimized.
But getting as much silver out as possible first from mixed solutions was very important.
It is also doable with pH higher than 2, and I observed maybe slightly quicker reaction, but when you raise pH past 2, quite a bit of base metals hydroxides can come out of solution during the process. You can eventually wash the precipitate with some acid to get rid of them, but I prefer to run at pH 2 and consistently getting 99+% Pd.
Yeah, silver need to be eliminated beforehand, as it will also drop with Pd. This is the whole culprit of the process, because HCl or NaCl precipitation of AgCl always drag Pd into precipitate and this is never washed free of Pd. My experience is between 0,2-0,7% Pd stay in AgCl, if feed was AgPd30 alloy. Not terribly much, but it need additional processing, which is extra step - redissolving in nitric and scavenging traces of Pd with DMG. I don´t know how well silver cell will cope with this Pd ammount in silver tho - never ran the Pd contamined raw silver through.
Do you have these documents somewhere ? I will like to read about it, if you can share them
Same here, i looked in the researchgate but found nothing usefulDo you have these documents somewhere ? I will like to read about it, if you can share them
Same here, i looked in the researchgate but found nothing usefuDo you have these documents somewhere ? I will like to read about it, if you can share them
Can you give me detailed steps for the process orvi , is it as follows : you raise the ph up to a point betweeb 2 and 4 then you bring the solution to a boil then you start adding the formic acid, am i correct ?
Edit for correct spelling in bold
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I had only written down the summarized protocol. All the search results now are focusing on using palladium and formic acid for hydrogen production or reducing organic compounds and nitrate.
I can't find the old links because the searches have hundreds of these new papers using the same chemicals for totally different processes!
I did manage to find one from Sciencedirect which mentions formic acid as part of the recovery process, but it's not the article where formic acid reduction was the core subject, optimizing the reagents and conditions: https://www.sciencedirect.com/science/article/abs/pii/S0926860X05009075
It does show an optimized and cost-effective process for DISSOLVING Pd in HCl-H2O2, with the exact conditions for this! Nitric isn't required! 7% HCl, 5% H2O2, 10 to 1 ratio of liquid to solid material, heat to 60C for 2 hours, and it was all dissolved!
This paper got 98% purity, with a near complete (>99%) recovery of Pd from the scrap material.
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If my memory serves me right I seem to remember something about Formic acid or maybe Sodium formate in Hokes book too.
I seem to remember it was hard to find when I tried to dig it up again though.
Chapters X and XIV, mainly XIV.
Dave
Dave
Looks like it'll be up to us to optimize the protocol ourselves! We have the basic protocol, at least. It's just a matter of testing variations to see what works best.
Above, I posted link to my AgPd alloy on FeCu carriers - refining via formic acid/NaOH. Not perfect, but I obtained 99.4 % Pd at the end. It isn´t that complicated at all, one thing that you really need is patience and good hood, due to possibility of CO formation from partial oxidation of formic acid.
Additionally, it is wise to wash Pd sponge with 5-10% H2SO4 to clean it from possible entrapped base metal hydroxides, that could be dragged with Pd when precipitating.
Higher you go with pH, I found the reaction somewhat quicker, but I will advise to stick to pH around 2. Remove all silver diligently beforehand, as it will also co-precipitate with Pd as metallic Ag.
I do not have experience with formate reduction of other PGMs or their mixtures tho. So I do not have first hand experience of eg PtPd solutions reduction. Apparently, it should work fine.
Be careful with Pd microparticles, they can be pretty high fire hazard if somewhere close flammable gasses or solvents, espetially hydrogen or nat gas. Pd and Pt are catalytic, be aware of this fact. Carefully wipe all of the residues with wet towel and store these wipes wet before incinerating and recovering values. Just to be sure
I do most of my refining outside, well away from the house! Only HCl wash steps are in a more enclosed space.Above, I posted link to my AgPd alloy on FeCu carriers - refining via formic acid/NaOH. Not perfect, but I obtained 99.4 % Pd at the end. It isn´t that complicated at all, one thing that you really need is patience and good hood, due to possibility of CO formation from partial oxidation of formic acid.
Additionally, it is wise to wash Pd sponge with 5-10% H2SO4 to clean it from possible entrapped base metal hydroxides, that could be dragged with Pd when precipitating.
Higher you go with pH, I found the reaction somewhat quicker, but I will advise to stick to pH around 2. Remove all silver diligently beforehand, as it will also co-precipitate with Pd as metallic Ag.
I do not have experience with formate reduction of other PGMs or their mixtures tho. So I do not have first hand experience of eg PtPd solutions reduction. Apparently, it should work fine.
Be careful with Pd microparticles, they can be pretty high fire hazard if somewhere close flammable gasses or solvents, espetially hydrogen or nat gas. Pd and Pt are catalytic, be aware of this fact. Carefully wipe all of the residues with wet towel and store these wipes wet before incinerating and recovering values. Just to be sure
So orvi i did read the whole thread of yours, thats a beautiful bead of palladium tbh.Above, I posted link to my AgPd alloy on FeCu carriers - refining via formic acid/NaOH. Not perfect, but I obtained 99.4 % Pd at the end. It isn´t that complicated at all, one thing that you really need is patience and good hood, due to possibility of CO formation from partial oxidation of formic acid.
Additionally, it is wise to wash Pd sponge with 5-10% H2SO4 to clean it from possible entrapped base metal hydroxides, that could be dragged with Pd when precipitating.
Higher you go with pH, I found the reaction somewhat quicker, but I will advise to stick to pH around 2. Remove all silver diligently beforehand, as it will also co-precipitate with Pd as metallic Ag.
I do not have experience with formate reduction of other PGMs or their mixtures tho. So I do not have first hand experience of eg PtPd solutions reduction. Apparently, it should work fine.
Be careful with Pd microparticles, they can be pretty high fire hazard if somewhere close flammable gasses or solvents, espetially hydrogen or nat gas. Pd and Pt are catalytic, be aware of this fact. Carefully wipe all of the residues with wet towel and store these wipes wet before incinerating and recovering values. Just to be sure
You mentioned that copper and Fe can be eliminated with diluted nitric acid and small additions of sulphuric acid. In my case the mlccs i have are about 4 kilo grams of mixed types(old school mlccs and new ones) and i finely powdered them and got rid of the copper legs using a fine mesh
So now the palladium foils are finely grounded. The question now is :
Will the diluted nitric that is used to get rid of copper dissolve some of the palladium because its finely powdered ?
Yes, it will. I hate wet route for ceramic based materials, as it is never complete and very tiring. And you need to get rid of silver firstly, so nitric leach is necessary. But it probably won´t recover all values. So after that, you will need to continue with AR.
Then ill go directly with concentrated nitric acid and ill give high heat for 2 to 3 hours
Tin will be turned to insoluble metastannic acid and most of the nickel will not be dissolved
Mostly Silver copper and palladium will be in the solution.
After filtration ill precipitate silver with enough amount of hcl
Then collect my silver and precipitate palladium with formic acid using your way.
You mentioned that copper will not precipitate if the ph is around 2
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