Rhodium refining from white gold jewellery scrap

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GSR

Member
Joined
Sep 20, 2021
Messages
18
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 are this related to your previous posts?
If so it should be kept there.
The only Rhodium in white gold should be the plating.
And that is very small amounts.
 
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.
 
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.
 
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.
 
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.
 
GSR are this related to your previous posts?
If so it should be kept there.
The only Rhodium in white gold should be the plating.
And that is very small amounts.
PGM content of white gold correlates closely with karat measurement of the object, It's age, country of origin, and maker. Srwetips took the time to chart out his observations in one of his videos in YouTube.
 
PGM content of white gold correlates closely with karat measurement of the object, It's age, country of origin, and maker. Srwetips took the time to chart out his observations in one of his videos in YouTube.
I’m not commenting PGMs in general.
Only Rhodium in this case, and I don’t think you will find much Rhodium inside white gold unless it is very old, and then just as “contamination” in Pt/Pd.
 
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.
Is this an observation? I’m thinking that Rhodium plating is so very, very thin as to disintegrate if the underlying metal is digested, but I suppose electroplated jewelry plating might be thicker than I thought.
 
Rhodium is used in jewelry to illuminate diamond settings so they shine. The layer of plating is very thin and when gold alloy with a rhodium plating is dissolved in aqua regia the flakes remain with the insolubles. The layer is very thin. If you were to melt gold alloys with rhodium plating the rhodium would alloy with the gold and remain in low enough concentrations that it is not observed in the insolubles. So apparently it dissolves. I have never noticed a stannous stain indicative of rhodium when processing jewelry scrap in aqua regia.
 
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