# Palladium Refining without using DMG



## GSR (Apr 17, 2022)

Hi there, I've been refining Palladium from scrap white gold jewellery using DMG for some time now. I find it very time consuming, using large volumes and does not seem to extract the Palladium to completion. Does anyone know of an easier way to separate and refine Palladium from the nitric acid digestion of inquarted gold jewellery?


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## orvi (Apr 17, 2022)

GSR said:


> Hi there, I've been refining Palladium from scrap white gold jewellery using DMG for some time now. I find it very time consuming, using large volumes and does not seem to extract the Palladium to completion. Does anyone know of an easier way to separate and refine Palladium from the nitric acid digestion of inquarted gold jewellery?


After inquartation, you are left with mainly Ag and Pd as noble metals in solution. Simple NaCl pour will separate silver from palladium, which could be then recovered on copper. Refining will be harder


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## M Usmani (Apr 18, 2022)

Dear Palladium will precipitate or make layer on copper?


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## Yggdrasil (Apr 18, 2022)

M Usmani said:


> Dear Palladium will precipitate or make layer on copper?


If you are cementing Platinum group metals on copper. 
You NEED to have a vigorous stirring to dislodge the cement before it passifies the copper with a layer of said metal. 
Air bubbling, stirring or what ever the creates turbulent flows in the liquid.


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## orvi (Apr 18, 2022)

M Usmani said:


> Dear Palladium will precipitate or make layer on copper?


You need constant agitation for the particles to fall off the copper surface. Either strong stirring or bubbler. Otherwise, the PGM deposit will form layer, protecting the copper surface from further reaction.


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## GSR (Apr 18, 2022)

Thanks for all your responses but scrap jewellery can have more than just silver and palladium in the nitric acid digest. So I need to be able to selectively separation Palladium. Cementing will not be effective. How can I precipitate or separate Palladium without DMG or cementing? Any other ways?? thanks for your responses.


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## M Usmani (Apr 18, 2022)

Yggdrasil said:


> If you are cementing Platinum group metals on copper.
> You NEED to have a vigorous stirring to dislodge the cement before it passifies the copper with a layer of said metal.
> Air bubbling, stirring or what ever the creates turbulent flows in the liquid.


very well noted with thanks


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## M Usmani (Apr 18, 2022)

orvi said:


> You need constant agitation for the particles to fall off the copper surface. Either strong stirring or bubbler. Otherwise, the PGM deposit will form layer, protecting the copper surface from further reaction.


Thanks a lot


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## nickvc (Apr 18, 2022)

A simple way to recover your Pd is to directly dissolve your 18k alloy with AR , filter your solution which will separate any silver as a chloride , precipitate your gold and allow to settle fully and then cement using copper sheet or bars but as advised use an air bubbler so the Pd doesn’t pacify your copper, unless you have other PGMs in the solution Pd should be the only metal to cement.


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## Alondro (Apr 18, 2022)

nickvc said:


> A simple way to recover your Pd is to directly dissolve your 18k alloy with AR , filter your solution which will separate any silver as a chloride , precipitate your gold and allow to settle fully and then cement using copper sheet or bars but as advised use an air bubbler so the Pd doesn’t pacify your copper, unless you have other PGMs in the solution Pd should be the only metal to cement.


So, for this method, you precipitate gold BEFORE recovering Pd? Using metabisulfite, I assume? I ask, as this might be a useful method for old IC chips and EPROMS I have about 10 pounds of now, which vary the PMs on the plating on the inside tips of the prongs, where the gold bond wires attach.


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## eaglekeeper (Apr 18, 2022)

After you recover the silver and gold from solution, I believe you can use formic acid to reduce Pd from the solution. I have used that process on Pt with no problem, but I have never used it for Pd (hopefully someone with more experience will chime in). Just keep in mind that formic acid will also reduce any other residual precious metal that may still be in solution.

I believe Owltech on YouTube has a couple videos using formic acid reduction.






Tube


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## orvi (Apr 19, 2022)

Yes, formic acid will work. It eventually reduce everything precious, but base metals will stay in solution. More suitable for larger quantities than DMG.


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## orvi (Apr 19, 2022)

GSR said:


> Thanks for all your responses but scrap jewellery can have more than just silver and palladium in the nitric acid digest. So I need to be able to selectively separation Palladium. Cementing will not be effective. How can I precipitate or separate Palladium without DMG or cementing? Any other ways?? thanks for your responses.


It don´t come to my mind what else could mess up palladium recovery. Maybe trace platinum, but I don´t expect to be of some appreciable percentage. And only fraction of it likely goes into the solution, certainly not all of it. Ruthenium and rhodium won´t dissolve in these conditions. Ir and Os, I doubt they could be present, and if they will be, they won´t dissolve either. Gold won´t dissolve. Mercury - i think that this isn´t in jewellery. No more precious metals exist - so just Pt could be the case, in my opinion.

From inquart, NaCl/HCl Ag removal is a classical step, if you do have Pd inside. Very convenient and sharp separation of Ag and Pd - certainly cheapest. You will end up refining Pd anyway, if you want to get it to 3N purity for selling. If not, some 1-2% of other metal impurities are not the issue, if you do not chase premium.


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## GSR (Apr 19, 2022)

thanks to all your responses. I think I'll try the two suggestions offered. 1) using formic acid to reduce Pd and 2) using copper to precipitate Pd AFTER silver and gold are removed from solution.


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## GSR (Apr 19, 2022)

nickvc said:


> A simple way to recover your Pd is to directly dissolve your 18k alloy with AR , filter your solution which will separate any silver as a chloride , precipitate your gold and allow to settle fully and then cement using copper sheet or bars but as advised use an air bubbler so the Pd doesn’t pacify your copper, unless you have other PGMs in the solution Pd should be the only metal to cement.


But will AR dissolve 18k alloy??? I thought that a silver chloride layer would form and protect gold from dissolving - that's why inquartation and nitric digestion was necessary before AR step.


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## GSR (Apr 19, 2022)

orvi said:


> Yes, formic acid will work. It eventually reduce everything precious, but base metals will stay in solution. More suitable for larger quantities than DMG.


this is a great suggestion thank you! But why does formic acid reduce only precious metals and not base metals????


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## kurtak (Apr 19, 2022)

GSR said:


> But will AR dissolve 18k alloy??? I thought that a silver chloride layer would form and protect gold from dissolving - that's why inquartation and nitric digestion was necessary before AR step.


The silver chloride problem is only a problem when the silver in the alloy is (relatively speaking) high other wise it/s not a problem - so it depends on the alloy

there is LOTS of karat gold that has little or no silver in it

Examples; - 18k "yellow" gold = 75% gold 25% silver - so the silver is high = silver chloride "problem --- 18K "red" gold = 75% gold 25% copper - so no silver chloride problem = can go direct to dissolving in AR

Kurt


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## Alondro (Apr 19, 2022)

eaglekeeper said:


> After you recover the silver and gold from solution, I believe you can use formic acid to reduce Pd from the solution. I have used that process on Pt with no problem, but I have never used it for Pd (hopefully someone with more experience will chime in). Just keep in mind that formic acid will also reduce any other residual precious metal that may still be in solution.
> 
> I believe Owltech on YouTube has a couple videos using formic acid reduction.
> 
> ...


Yes, I've seen that video. He was recovering Pd and Ag from the bulky old block ceramic capacitors. The combination was alternating sodium carbonate and formic acid additions until the solution became gray and full of fine powder.

It was a a method you can find a patent on as well, with a clearer description.

I also found an interesting method from Researchgate using 60% sulfuric with 0.1M NaCl heated to 125C for 10 hours for dissolving effectively 100% of PGMs from powdered catalytic converters. The charts the scientists did confirmed that these were the optimal conditions. The chloride complexes were then much easier to reduce.


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## orvi (Apr 19, 2022)

GSR said:


> this is a great suggestion thank you! But why does formic acid reduce only precious metals and not base metals????


Everything has its own redox potential. Formic acid in basic enviroment has enough reducing power to reduce noble metals above copper, but it fail to reduce copper and base metals. It is fairly selective in this manner, but if you have Ag together with say Rh and Pd, Au etc... All will be reduced. 
SMB is fairly selective for gold - it will not precipitate for example silver.


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## eaglekeeper (Apr 19, 2022)

Most of my Pt comes from catalytic converters. In those cases there is little to no base metals involved, so I just cement the Pt with zinc. But there are times I find Pt in Ewaste and that means base metals present. So that is the only time I use formic acid to reduce the Pt.

Getting the PH right for formic acid reduction is a little tricky. If the solution becomes too basic you risk the chance of forming base metal hydroxides. You would have to be pretty high on the Ph, but it's possible.

I don't like the idea of handling near boiling toxic solutions, so formic acid (at least for me) is used as a last resort.


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## GSR (Apr 21, 2022)

orvi said:


> Everything has its own redox potential. Formic acid in basic enviroment has enough reducing power to reduce noble metals above copper, but it fail to reduce copper and base metals. It is fairly selective in this manner, but if you have Ag together with say Rh and Pd, Au etc... All will be reduced.
> SMB is fairly selective for gold - it will not precipitate for example silver.


thank you !


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## PeterM (Apr 22, 2022)

GSR said:


> thank you !


Nice Post, because using DMG gives me the Willies, just from the smell of it alone. Actually, Formic acid does a lot of good things. THANKS...


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## Alondro (Apr 22, 2022)

PeterM said:


> Nice Post, because using DMG gives me the Willies, just from the smell of it alone. Actually, Formic acid does a lot of good things. THANKS...


Formic acid is actually used as a food preservative at low concentrations. It's only toxic at high levels. Diluted... it's basically what gives some ants that weird smell.


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## eaglekeeper (Apr 22, 2022)

Formic acid is also used by Bee keepers to control mites in their hives... It's easy to get off Amazon. When using it for a reduction, a little goes a long way.


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## orvi (Apr 23, 2022)

eaglekeeper said:


> Formic acid is also used by Bee keepers to control mites in their hives... It's easy to get off Amazon. When using it for a reduction, a little goes a long way.


Molar mass is a thing that could make interesting comparisons. Take for example Ag(NH3)2+ ions in solution. Adding sodium borohydride will reduce silver to metal. Molar mass of the borohydride is so low, that weight ratio is theoretically nearly 1 kg of reduced silver with 40 g of borohydride  in reality, far more should be used because of side reactions, and all in all it is not the best way how to do this... But it shows the point.


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## orvi (Apr 23, 2022)

PeterM said:


> Nice Post, because using DMG gives me the Willies, just from the smell of it alone. Actually, Formic acid does a lot of good things. THANKS...


Formic acid is also one of that chemicals, so pleasant, that you do not want to open the flask  Formate salts are OK. Also it is good to know that under some circumstances, formic acid could decompose to carbon monoxide.


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## PeterM (Apr 23, 2022)

orvi said:


> Formic acid is also one of that chemicals, so pleasant, that you do not want to open the flask  Formate salts are OK. Also it is good to know that under some circumstances, formic acid could decompose to carbon monoxide.


Good to know, I have used it to slow down ion exchange reactions.


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## Alondro (Apr 23, 2022)

orvi said:


> Formic acid is also one of that chemicals, so pleasant, that you do not want to open the flask  Formate salts are OK. Also it is good to know that under some circumstances, formic acid could decompose to carbon monoxide.


Yup, like sodium formate, which is used as a de-icer on airport runways because it's non-corrosive. It's not used on roads because it's more expensive than sodium or calcium chloride.


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## Tony S (Apr 24, 2022)

Alondro said:


> Formic acid is actually used as a food preservative at low concentrations. It's only toxic at high levels. Diluted... it's basically what gives some ants that weird smell.


Thank you for this. If I dissolve mining ore with HCL + Hydrogen Peroxide rather than AR, could I then use formic acid to precipitate any nobles? What is the procedure in termps of Ph, temp etc? Thank you


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## Alondro (Apr 25, 2022)

Tony S said:


> Thank you for this. If I dissolve mining ore with HCL + Hydrogen Peroxide rather than AR, could I then use formic acid to precipitate any nobles? What is the procedure in termps of Ph, temp etc? Thank you


I don't know if HCl + H2O2 will dissolve the PGMs very well, and if it touches silver at all, it will form insoluble silver chloride at once which will be trapped within all the other debris from the ore. 

HCl + bleach works better for dissolving gold, unless you're dealing with sulfide ore. Then the H2O2 turns the sulfide into sulfur dioxide... which is a nasty gas you don't want to breath in when it's bubbling out violently! Also, the ore needs to be very finely powdered for the process to work properly. You could also roast the ore, which is a bit safer. It still releases sulfur dioxide, but doesn't cause a rather violent chemical reaction, which you get when you dump peroxide into finely powdered sulfides.

I've never used the process myself, but I believe you do not need to add HCl when oxidizing the sulfides. Only H2O2. I found a research paper that also noted something interesting: at a pH of around 9 in an aqueous solution, the sulfides oxidize to sulfate, sulfite, and thiosulfate, and don't release SO2, . And fascinatingly, the reaction proceeded 5X FASTER when the solution was COOLED! As the reaction went to completion, most of the sulfur compounds were converted to sulfates, except for a mystery sulfur compound the researchers could not identify. https://onlinelibrary.wiley.com/doi/abs/10.1002/kin.10118

This appears to present a safer way to oxidize sulfides in finely powdered ore samples. Mix them in a cold aqueous solution and slowly add peroxide, keeping the reaction vessel in an ice bath.

To dissolve gold with HCl + bleach, only a tiny amount of bleach is needed, especially if there's only a small amount of fine gold. 

Formic acid + sodium carbonate appears to only work for palladium. You'll want to look up the protocol. There are very well-described methods online with explicit detail, described by proper chemists who've outlined all the conditions. It'd be easier to find one of those protocols than for me to try to re-write the whole thing.


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## GSR (Apr 30, 2022)

GSR said:


> thank you !





GSR said:


> thank you !


just wanting to understand how best to use formic to precipitate out the Pd. I've cemented a solution that has essentially only Pd left in it. If I take this cemented solids and digest in HNO3 and dissolve the Pd what do I do then?


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## jphayesjr (May 16, 2022)

Since fire assay techniques are likely to be a part of the palladium refining process each of us uses, here's a link to a free legal downloadable copy of Bruno Kerl's classic "The Assayer's Manual." The Assayer's Manual Amazon is selling hard copy for @26.95 Enjoy.


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