AuPd plated pins processing

[orvi]

So, I acquired some old boards with connectors made in eastern Germany way back in 80s. To my surprise, quick "assay" (melt+XRF of the button) revealed that they are plated with gold and palladium. 4-5g/kg Pd and 3-4 g/kg Au to be more precise. I will have around 500-700 grams of them in the end. Some of them are higher grade (6-8g Pd/kg), some of them are lower grade (2g/kg Pd).

I know that it won´t be that much of a work to resolve Pd and Au. I plan to drop the gold with SMB or ferrous sulfate (once I read here that ferrous sulfate is better when platinum is in solution, but I don´t know how Pd would behave - and if it will be dragged with Au). Then scavenge Pd with DMG.

But there is numerous methods which can be performed. If anyone has working, tested procedure on how to resolve Pd and Au from AR solution, I would greatly appreciate it.

orvi

 

[nickvc]

Orvi why not once you have precipitated your gold simply cement the palladium with copper as then you will have metallics rather than salts to deal with.

 

[orvi]

Orvi why not once you have precipitated your gold simply cement the palladium with copper as then you will have metallics rather than salts to deal with.

As PGM precipitation on copper is very good way, there would be considerable copper in solution. And I know from my experience that it is very difficult to completely cement the PGMs from heavy copper solutions - due to redissolution issue with oxygen. It can be done by reduction of all CuCl2 to CuCl (obtaining the dark solution). Second reason is I do not have place for the cementation rig in my fume hood - there are multiple reasons why, one of which is that it will sting into eyes of some people, as I am doing it in my work.

But I can alternatively use copper powder to accomplish this. Stir copper powder in covered beaker for few hours, then decant the solution and scavenge last bits of Pd with DMG.

 

[nickvc]

Instead of stirring try a good air bubbler with a cover on the beaker.

 

[orvi]

So, I dissolved the lot in AR - 700g in total. There was mix of pins, some were brass, but majority was bronze. After successful dissolution, I denoxed with sulfamic acid. Then things started to behave strange.
As I added SMB to the solution, very violent evolution of SO2 began. I processed a lot of material, but I never had such a reaction - just on the surface of liquid. So I stirred the solution fairly well and added SMB dissolved in water. Again, very violent eruptive reaction, but this time, some SO2 passed to the solution and dropped the gold - at least, majority of it (stannous is slightly positive/unconclusive on this one).

BUT, I proceeded anyway to drop the Pd with DMG. And another strange observation - I measured 10 g of DMG (excess for the Pd I expected to be inside) and added with stirring. As usual, done dozens of times before... NOW, Pd(DMG)2 complex completely refuse to precipitate. I can still detect fair Pd with stannous in solution despite several hours of stirring. pH of the solution is below 1. But not much free HCL is in there.
I must say that solution is nearly black in colour (overload of SMB added in effort to drop the gold), yet not all gold dropped. Maybe the solution formed some sulfito-complexes, that somehow block the formation of the complex... But there I am not sure at all.

What would be logical to do next ? What to try ?
As I fear it and don´t want to use it if it isn´t necessary - I thought about using hydrazine.HCl as reducing agent, that will reduce both Au and Pd from the vast ammount of liquor (4 L) to some small bit of precipitate. Does it work in just slightly acidic conditions on both Pd and Au ? Or it need some special treatment ?
Formate reduction of this quantity of very diluted values solution seems inefficient to me. But if somebody has experience with it, please let me know. I have means to heat this pot to 80-90°C, so theoretically, it should be possible. Does formate in these conditions also reduce gold to the metallic form ?

Unfortunately, I cannot cement the solution on copper right now, as I cannot setup cementing rig with bubbler in my place.

 

[Martijn]

And I know from my experience that it is very difficult to completely cement the PGMs from heavy copper solutions - due to redissolution issue with oxygen.

Orvi, i think this post will help you out: Geo has a devised a way of getting the Pd from AP. So that copper in solution should be no problem.
https://goldrefiningforum.com/posts/323112/

 

[orvi]

Yeah, I thought about that. In the end, I would have done much better if I used copper for several days with exclusion of air.

Friend of mine, who do similar scrap more often just told me to stir it for one day - that DMG in acidic choride enviroment act very slowly on palladium. And yes, he was right. I let whole pot stir overnight on magnetic stirrer, and in the morning I was able to filter the DMG complex.
I must admit that I hate incineration of DMG complex. So next time, I wouldn´t proceed this way. I will certainly cement on copper and scavenge last bits of Pd with DMG.

Anyway, I was able to scavenge all Pd from solution, incinerate the DMG complex to nice sintered sponge in induction furnance and results are promising. From 700g of pins, only 530g was AuPd, rest were just Au.
And I got 2,90g Pd of ca 96% purity. Some ultrafine gold was also trapped in the precipitate, that is why 1% Au.

I have also 4+2 more spare connectors of AuPd pins left, so next time when I won´t be busy, I will dissolve these in AR (around 40g) and try to drop the Pd with formate. I expect that gold will also drop with formate, but anyway... If it would proceed in that dilution and produce OK metallic precipitate, I would go this way. Much easier to work with 50 mL of solution than with 4 liters.
Solution will be still hot, adding formic acid, so there would be just addition of NaOH to strirred solution until pH ca 2 and heating for few hours.