Rhodium refining from white gold jewellery scrap

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GSR

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Sep 20, 2021
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Hi there, I recently refined gold, silver and palladium from a white gold jewellery digestion. After precipitation the gold from the aqua regia solution I noticed the solution had an olive greenish colour. It did not test using stannous chloride. I decided to add zinc to cement out resulting in a fine black powder. Could this be Rhodium? If not what else could it be? thanks
 

GSR

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Sep 20, 2021
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I digested with nitric acid first so Pd, Ni and Cu were released then. The remaining white gold residue was then digested in aqua regia so I suspected only Au and Rhodium might be left. Once I precipitated gold out ... only then did I use Zn to cement out the rest. So what could the black precipitate be? I know Rhodium plating is used for white gold so thought it might be that.
 

zacchy

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Jun 1, 2013
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I think Lou once posted that the presence of rhodium in mother liquor turned olive green, but I'm not sure if he was the one who said it. Rhodium = olive green mother liquor.

You can analyze the black powder that you precipitated with zinc, to see if there is a presence of Rhodium in that black powder.
 

4metals

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Rhodium plating on jewelry does not dissolve in aqua regia it remains as bright shiny flakes. It is often a residue when doing stone removal and while it looks like a lot, the weight is quite small as the rhodium is a flash plate and very thin.
 

NanoCat

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Mar 16, 2018
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I think Lou once posted that the presence of rhodium in mother liquor turned olive green, but I'm not sure if he was the one who said it. Rhodium = olive green mother liquor.

You can analyze the black powder that you precipitated with zinc, to see if there is a presence of Rhodium in that black powder.
got a quickie method to analyze for Rh in the black powder? My mother liquor does come out olive green. I cooked about 34g of the Carbon reduced powder in HCl with KClO3 oxidizer really hot for about 12 hrs. (The powder had gone through 20% Sulfuric wash for hours that gave a bluish Cu looking solution.) Most of the blacks are still there; dried under bright light microscope the particles are really small reflective white metal. I used to plate Pd on jewelry so I know that dull dark grey look; this isn't Pd. I have a light yellow solution that I'm boiling down to drop with NH4Cl or DMG.
 

au-artifax

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got a quickie method to analyze for Rh in the black powder? My mother liquor does come out olive green. I cooked about 34g of the Carbon reduced powder in HCl with KClO3 oxidizer really hot for about 12 hrs. (The powder had gone through 20% Sulfuric wash for hours that gave a bluish Cu looking solution.) Most of the blacks are still there; dried under bright light microscope the particles are really small reflective white metal. I used to plate Pd on jewelry so I know that dull dark grey look; this isn't Pd. I have a light yellow solution that I'm boiling down to drop with NH4Cl or DMG.
4metals had it exactly right. There is no way you put rhodium into solution with the methods you used. And NO, rhodium does not give an olive green hue to a soltion....Period! If you want to know what rhodium in solution looks like, then go to any website regarding rhodium plating solution and look at the color. It is as 4metals said, it doesn't dissolve and is left behind in the form of bright white metal flakes. Peroid! If you accept this I will give you some tips on collecting it for future refining. I will wait and see though.
 

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