Precipitating Pd from Aqua Regia Solution

GSR

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Sep 20, 2021
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Hi there, hoping someone can help me. I usually extract Pd using nitric acid and then precipitate salt with DMG. On this occasion of refining jewellers sweep that were mainly 18k gold, Pd did not extract with nitric acid. It did extract when I used Aqua Regia however and tested red using SnCl2 indicator after I precipitated out the gold with MBS. Now I have an aqua regia solution that tests positive for Pd but DMG is not pulling it out of solution?? Any ideas?? Its probably the presence of HCl in the solution right? What can I do now?

Thanks
 

Yggdrasil

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Do not double post, it is against the forum rules.

Someone will answer you soon.
In the mean time. I think you need to denox
the solution first.
The HCl with the oxidizing Nitric will most likely just redissolve it immideately.
 

GSR

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Yes you raise a good point however the sample is a jewellers sweep and they confirmed that they use 15% Pd in their white gold which makes up half their jewellery making. So I'm pretty confident that Pd is in there.

Do you believe that Pd should drop out with DMG in aqua regia solution?
 

GSR

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yes I'm sorry I double posted by accident. First time on the site and was looking through different areas and then posted my query and realised I posted it on this area incorrectly. Won't happen again.

So you think I should try to boil off the excess nitric or maybe add sulphamic acid? If only HCl present, should the yellow precipitate form you think?
 

GSR

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ok thanks for that advice. I'm certain there is Pd in there so will try to cement out.
 

nickvc

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When cementing PGMs you need to agitate the solution so add a bubbler or the palladium will likely plate onto the copper and stop any further cementation.
 

Lino1406

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Mo with stannous gives blue if I'm not mistaking. Molybdenum chlorides can be also green,brown red. One of the molybdenum oxides is blue. Stannous check red = Pd, Pt, Rh...
 

Yggdrasil

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There was a discussion a few months ago where it was claimed by members that Mo gave red indications.
And since there wasn't presented evidence of the contrary I accepted it as a fact.
I'd be happy to be corrected so my info will be correct next time.
 

Lou

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Mo gives more of a dirty brown orange. Lots of stannous and it will go blue, as will tungsten.
 
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