Selective precipitation of rhodium

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Inter Refiner

Well-known member
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Apr 19, 2020
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46
Hello friends,
I have a pgm powder of pt, pd, rh, I dissolved them in aqua regia, but now I need to selectively precipitate rhodium from the solution without precipitating pt or pd, is there any chemical or a process to do that.

Thank you for your time
 
Maybe this helps:
"The selective precipitation of rhodium was performed with (NH(4))(2)S from platinum free raffinate with a recovery of >99%." from:
https://www.researchgate.net/publication/225184454_Separation_of_platinum_and_rhodium_from_chloride_solutions_containing_aluminum_magnesium_and_iron_using_solvent_extraction_and_precipitation_methods

First use selective precipitants for the Pt and the Pd i would guess. You' ll have only the rhodium left and can cement that or precipitate.
 
Martijn said:
Treating the powder with concentrated nitric acid would dissolve the Pd before going to AR.
Click to expand...

heating the soln of Pt Pd Rh powders (in my case Zn-cemented) in HNO3 resulted in dissolution of Pd alongside Pt, but the soln was boiled for 2 days. never gone to completion in terms of Pd in the solid residue (about 20-30% of Pd stayed in the cake), i dont know why this happened, but it was XRF measured in various stages.
separating Rh from PtPd is very tricky process, mainly if th Rh content is low.
 
Some amount of the Pd was PdO which for all intents and purposes is inert to any acid that's not HBr or HI.
 
Now I got a bit confused.

In an earlier post a few years back, I claimed the same and was then clearly told that PdO dissolves in HCl.
Still beeing a rookie I accepted the correction.
Now we are told the opposite, so if you don't mind Lou,
can you elaborate a bit?
 
Thanks Lino :D
But if you read the question once more,
it does not help to explain whether or not PdO
dissolves in HCl.

Do it dissolve, but in minute amounts
or do it dissolve in reasonable amounts?
 
Iridium and rhodium may be precipitated with diethylene triamine. These
precipitation reactions can be used to separate rhodium and iridium from each
other.
 
Yggdrasil said:
Thanks Lino :D
But if you read the question once more,
it does not help to explain whether or not PdO
dissolves in HCl.

Do it dissolve, but in minute amounts
or do it dissolve in reasonable amounts?
Click to expand...

Well, when there are hydroxides that are produced by borohydride in mother waters, I have seen that the bottom of this mud is not attacked by aqua regia ... I did not think it was PdO
 
Usually borohydride product is completely soluble in aqua regia. It has a high enough surface area.

What are you trying to do?
 
justinhcase and Lou, friends.
Organic Precipitation
Organic reagents can be used to separate metals by selective precipitation.
Palladium can be precipitated with dimethylglyoxime. This reaction is used to
remove palladium in platinum purification.
Iridium and rhodium may be precipitated with diethylene triamine. These
precipitation reactions can be used to separate rhodium and iridium from each
other.

Diethylenetriamine (DETA) I think this method is used by Heraeus
 
I can't comment on other refiners using DETA or its salts but can say that it works very well in certain circumstances/solution conditions as I said in another thread. Some people prefer to make the nitrite salt instead and take that to sponge as it is easier to remove Pt(IV) from that product than from the DETA product.

The best thing that can be done with Rh is to work with very concentrated solutions.
Rh is easily solublizied with sodium peroxide or molten salt chlorination. From those solutions it can be precipitated in strongly acidic solutions and the mother liquors sent to cementation.
 
Si, se puede tener las reducciones de bastantes aguas madres, este polvo negro fundirlo con algún persulfato de sodio o potasio en un crisol de cuarzo, pero creo que queda Rh contaminado, por lo regular, la sal de Claus tambien puede usarse para esto.
 
Lou said:
I can't comment on other refiners using DETA or its salts but can say that it works very well in certain circumstances/solution conditions as I said in another thread. Some people prefer to make the nitrite salt instead and take that to sponge as it is easier to remove Pt(IV) from that product than from the DETA product.

The best thing that can be done with Rh is to work with very concentrated solutions.
Rh is easily solublizied with sodium peroxide or molten salt chlorination. From those solutions it can be precipitated in strongly acidic solutions and the mother liquors sent to cementation.
Click to expand...
Lou, I was thinking about using NaOH/KOH fusion on the suspected Rh product. you have some details for this? sounds cleaner direct to Chloride: "molten salt chlorination"
 
You'll need an oxidant. No point in mixing either but I'd keep the KOH out of it.

It's six of one half dozen of the other. NaOH/NaNO3, Na2O2...etc.
 
thnx Lou, I found some Na2O2 in the chem cupboard. what ratio of each to the amount of insoluble metal powder? Temp? And NaCl in the fusion to get it to a Chloride?
 

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