jpsmith123
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Seperating Palladium from Pd/Ag Alloy
I've got about 5 grams of palladium/silver (60/40) alloy from which I would like to extract the palladium.
I was thinking of anodically dissolving it in dilute HCL, then adding some NH4OH (My chemistry and physics hdbk claims that AgCl is soluble in NH4OH,
7 grams per 100 grams of NH4OH), the PdCL2 would hopefully precipitate and then could be filtered out.
Does that make sense, or is there a better way?
Regards,
Joe
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Eclectic
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Dissolve the alloy in nitric acid, then precipitate the silver with HCl.
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Fleaker
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Use concentrated nitric to get it all into solution, drop out the AgCl, filter. Very pure ammonium chloride will drop out the palladium as palladium
ammonium chloride, a redish powder. That can be heated under an oxyhydrogen flame in an alumina crucible to get sponge form. From there you can
repurify with nitric and go other routes to get a high quality product.
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tantan
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I think PdCl2 is insoluble in water. Won't it be co-precipitate with AgCl?
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Fleaker
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True, but there is a time delay between precipitation. Anyway, you would simply dissolve the AgCl in ammonium hydroxide to accomplish the separation
of the salts.
I know that with a Ag/Pd/Pt solution silver goes first, then platinum, and upon the addition of sodium/potassium chlorate, the palladium will fall out
of solution.
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neutrino
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According to Lange, PdCl<sub>2</sub> is soluble in HCl.
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Fleaker
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That it is, but not exclusively. Other chloride salts go into solution with HCl, i.e. auric chloride.
It's just easier to separate the silver chloride and the palladium with the ammonium hydroxide and then heat to palladium chloride to reduce it
to sponge form.
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neutrino
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I don't think silver does that. I may be wrong here, but I think that palladium and gold are soluble because they form chloro-complexes, while
silver does no such thing. The common ion effect would make AgCl less soluble if anything.
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Fleaker
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I don't believe I said that silver chloride is soluble in HCl acid? I said it was soluble ammonium hydroxide, nothing whatsoever about
hydrochloric.
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jimwig
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See the recovering precious meals thread.
As refining and recovering are the same process.
[Edited on 29-7-2005 by jimwig]
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jimwig
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precipitate the Ag as AgNO3 using nitric acid.
then use aqua regia to solvate the Pd and ferrous sulfate (copperas) to precipitate the slude.
then dry and melt the sludge into a button
that's pretty high heat.
speaking of flames
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Fleaker
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Here's what I'd do:
If it's just a palladium/silver alloy dissolve it all in nitric acid, no need for aqua regia because palladium and silver both go into nitric.
From there you can precipitate the metals out as chloride salts, filter and wash it with distilled H20. Then as your chemistry book said, use about
35mL of NH4OH to dissolve the AgCl. That should leave the palladium as a residue in the bottom of the beaker. Filter it and rinse with NH4OH.
Afterwards you can heat the palladium salt to drive off the chlorine, and then you can melt it (easy enough to melt, 1550C, iron temps).
A thing to remember with most PGMs is that they should not be melted with a hydrocarbon fuel source because they form carbides. Consequently, they
shouldn't be melted in graphite crucibles nor silicon carbide, melt it in alumina or fused quartz and do it with oxyhydrogen or inductively
(assuming you can get ahold of either).
Jimwig, how would you precipitate the silver as AgNO3? That's soluble, it won't come down.
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jimwig
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my mistake i was thinking of purifying silver and using the chloride which I believe is insoluble (low).
i remember something about using sodium chloride and getting the precipitate.
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Fleaker
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Speaking of refining silver, this in an interesting method:
http://shorinternational.com/RefineAgInstruct.htm
Normally I just use KOH on the chloride (precipitated from the AgNO3 solution w/ sodium chloride/HCl) to get silver oxide and then smelt it with
charcoal. Here's the link...
But Kero Syrup 
organometallic reduction I think 
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