Hi all, I have read a good amount of CM Hoke, and I have a question. I am a trade jeweler processing my mixed gold and platinum scrap. I use palladium in my white gold and Pt solder, so there will be a fair amount of palladium going into solution. I really only want to recover the dissolved PGMs to the point where I know the values and can sell it, but I will be reusing gold, and any Pt pieces that do not dissolve. not So my question is - I understand that generally, after I drive off the nitric, I should drop out the Pt first with NH4Cl before the gold, but this will leave most/all of the Pd behind. So should I then add NaClO3 to drop the palladium before I drop the gold with SMB? Or should I do things in a different order? Thanks.
Precipitating Pt, Pd, then Au
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What quantities are you talking about in your karat scrap? How much of it is Platinum and how much Palladium?
The overall percentages of these metals in a refining lot, as well as the size of the lot, will determine the best approach for a jeweler / refiner.
The overall percentages of these metals in a refining lot, as well as the size of the lot, will determine the best approach for a jeweler / refiner.
Thanks. I have about 9 ozt of scrap. How that divides out is unknown. But I'd guess 3-4 ozt of plat - but a lot of that will be recovered as undissolved metal bits, 3-4 ozt of gold, and palladium unknown. Maybe half an ounce at most? I was also thinking maybe I should drop the gold out first, and then cement out the pgms with copper, treat them with nitric to recover the platinum, and then save the nitric dissolved palladium until I have more... Or maybe just take a small sample of the mixed pgms after cementing, and melt into a button and have it XRFd, and then send it all mixed to a refiner.
Is there Silver in the alloy? If so, how much?
anachronism
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Could you not dissolve the Palladium out first with Nitric? Along with and Silver that's in there leaving Gold and Platinum.
Not without some inquartation. And the inquarting and parting will prevent the re-use of insoluble Platinum if processed in aqua regia
The palladium is all alloyed into mostly 18K white gold, not separate scrap. And actually as I say this and think about it, half an ozt is probably generous.
There will be silver, but not a ton. Only what is used to alloy gold, which across all K and colors would average about 10%. So if there's 5 ozt of scrap gold, the very most there could be is about half an ozt.
Silver at 10% may stop all of the metal from digesting as the Silver Chloride will coat over the undissolved metals in aqua regia. You can clean it up but if it''s 10% it is a bit high. I assume if you expect to pick out the undigested Platinum after the digestion, you are not melting all of the scrap together before aqua regia, is this correct?
Thanks. Yes that's correct. I'm not melting it all together beforehand. I will be picking out any undigested platinum. So I can, if needed, pick out any larger pieces of gold if they develop a silver chloride crust, and clean them off to complete digestion. Most of the pieces are tiny, there are hundreds of them, and manual separation isn't realistic. Melting it all together isn't really realistic either. I can melt up to about 3 ozt of straight platinum together at once with my torch, but gold and platinum together is a different story because the gold melts, the platinum sinks to the bottom, and too much heat gets deflected by the gold to let the platinum melt unless I only melt maybe half an ounce at a time, which would take forever, and probably use a whole 5ft tall tank of oxygen if not more... and spoil a platinum crucible. If you can suggest a better process than going straight to AR, I'm all for it. Thanks for your help. What I really want to know though is should I drop the platinum first, then palladium, as salts, then gold, or should I drop the gold first and then cement out the PGMs? I'm not concerned at all about recovering the silver, but I also don't want to lose gold trapped up in the silver chloride either.
Also, if it's a good idea, I can run a magnetic stirrer in the AR while it's working...
A mixer will help and using cold aqua regia will help too. The Platinum will not digest in any appreciable amounts in cold acid but the gold will, even if it is slower. This may increase your Platinum recovery and lower the amount of Platinum in solution you have to reduce.
Also, if you are not melting it, process the white gold containing Palladium separately, it will simplify recovery.
Also, if you are not melting it, process the white gold containing Palladium separately, it will simplify recovery.
Thanks 4metals. Unfortunately, I can't separate the 18KPdW from the platinum. Aside from a few larger pieces, it's mostly all mixed 1mm +/- prong clippings. Hundreds and hundreds of them. Also, a lot of the platinum has 1500 solder on it which is 25% Pd. So, should I drop the platinum salts first, then palladium salts, then gold, or should I drop the gold first and then cement out the PGMs with copper?
Drop the gold first and cement the PM's. This will give you both metallic Platinum and Palladium in a very fine powder. You can separate the Palladium by leaching it out in nitric acid. The Platinum can be either digested and refined further or melted as dirty but not too dirty Platinum and sold to a refiner. The Palladium cam be dropped with Dimethylglyoxime and reduced to Palladium metal.
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That would have been my answer, but I wanted to let a true authority like 4metals guide you since I am just an amateur. I would drop the gold with ferrous sulfate. I assume he meant cement the PGMs.
4metals, could the palladium just be cemented out again after leaching the Pt / Pd with nitric instead of using DMG, or would too much PT follow the Pd into solution since it will be so fine?
Dave
Leaching the Platinum /Palladium with nitric will leave the Platinum with the insoluble fraction. The high nitric content of the parting liquor is best dealt with by using Dimethylglyoxime which will drop Palladium from a nitric solution. If you want you could part out the Palladium collect the insoluble Platinum and cement the Palladium on copper to yield metallic Palladium as well.
1mm pieces aren‘t so fine that a lot of Platinum will follow.
Still, as with all PGM work, a final stock
Pot for cementation is wise.
What happened? So I processed everything with AR, filtered out the silver chloride, divided it in half, cooked cooked half down, added HCL, cooked more wasn't getting brown fumes. To be sure I had killed all the nitric, I added sulfamic and it fizzed up a bit, slowly added more until it stopped. Filtered again resulting in a very small amount of particulates. Added SMB and the gold dropped out of the first half of my AR beautifully, mathematically returning slightly more than expected. So I proceeded with the second half in the same fashion, with one difference that I realized after. The first time, after cooking down, I had cooled the AR a bit with a few ice cubes, and further diluted it with some distilled water before adding the sulfamic acid. The second time, I also added ice cubes, but thinking back, I didn't dilute it further with distilled before I added the sulfamic. So the solution was a little hotter, and less diluted. When I added the sulfamic, a ton of red precipitate formed which I assume was my PGMs dropping out. Platinum? Palladium? Both? It took some effort filtering to get it all out, and I haven't added SMB yet to drop the gold. Just wondering what the pure red precipitate is, and why it dropped out from the adding the sulfamic when it didn't happen with the first half of my AR solution?
This also happened to me, and from then I never used sulfamic for PGM containing solutions de-NOx-ing. Probably some PGM sulfamate or mixed sulfate salt precipitating.
