# bothering



## arthur kierski (Aug 17, 2008)

something bothers me:when one extracts pgm from cats with ar,almost all the pgm goes to the solution---after gathering these pgms as a black powde(with zinc powder) and them separating them from each other again with ar,why rh stays left in the filter paper?should the second ar not dissolve all the pgm as it does in the first extraction(substrate+ar)???


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## lazersteve (Aug 17, 2008)

Arthur,

The first time around the Rhodium has likely formed a soluble alloy (or maybe an oxide :?: ) of sorts with the other PGMs. This may occur in the manufacturing process or as a result of exposure to high temperatures during operation of the catalytic convertor.

After using zinc to precipitate the PGMs they are all in a very finely divided form which brings out their individual properties. They are no longer an alloy, hence they behave differently.

A similar reaction to this is when Platinum is alloyed with silver it will partially dissolve in nitric acid, but when Platinum is not alloyed with silver, nitric acid won't dissolve it.

Steve


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## arthur kierski (Aug 17, 2008)

thank you for the quick reply---this doubt was with me since i read in ammens book --platinum of the world ( article)---there it happens something similar with platinum ores


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## Lou (Aug 17, 2008)

It is Rh2O3 that dissolves from the substrate. Bear in mind that the content level of rhodium (III) oxide is highly dependent on how old the converter is and what temperatures it ran. All highly variable.

Lou


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## arthur kierski (Aug 17, 2008)

thanks lou for the answer---


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## Froggy (Aug 17, 2008)

Tired of the HF acid!? :shock:Hmm, this appears to be a good thing Arthur? Steve is correct, from all indications the rh is already oxidized, it just comes off with the rest of the pgm's from the substrate (hopefully) sometimes it clings to the substrate and protects the other pgm's , as a coverter is used the Rh creates a oxidized cover over the substrate thus blocking the other metal from being put into ionic form, heat the filtered oxidized rh over 600f and wash with hcl. ......... I gotta give it to you Arthur, you are the most persistant converter junkie on the forum.. thx Frog


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## arthur kierski (Aug 17, 2008)

dear froggy----i persist with catalitic converters because i make a living with the rh that i extract(make 50 rhodium plating solution monthly) as for the hf ,i persist with it ----i just do not want to be disrespectful to the members of the forum who hates even the mentioning of this acid;so i decided not to talk about it---but i use it when i feel that is useful in my processing


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