Rhodium refining

[diego Henrique vilela]

Good afternoon friends, I took a rhodium-plated semi jewelry and attacked it with hno3. the rhodium powdered and the copper dissolved. but it generated a very large mass (looking like silver chloride) but there were no silver-plated pieces in that lot. Does anyone have an idea how to remove this bulky mass

 

[Martijn]

Rinse and wash the chloride with the rhodium powder, convert the silver chloride back to silver with sulphuric acid and iron (nails) wash and rinse the silver with distilled water, and start over. Use distilled water to dissolve it again. You had chlorine in your water. A lot, i guess. Ad some salt to see if more dissolved silver is left in the fitered solution. You couls also filter it crystal clear and reuse for the second dissolution.
Then filter off the rhodium and proceed as planned.
I assume the rhodium is left untouched by the sulphuric/iron step, but I'm not sure.

 

[diego Henrique vilela]

Rinse and wash the chloride with the rhodium powder, convert the silver chloride back to silver with sulphuric acid and iron (nails) wash and rinse the silver with distilled water, and start over. Use distilled water to dissolve it again. You had chlorine in your water. A lot, i guess. Ad some salt to see if more dissolved silver is left in the fitered solution. You couls also filter it crystal clear and reuse for the second dissolution.
Then filter off the rhodium and proceed as planned.
I assume the rhodium is left untouched by the sulphuric/iron step, but I'm not sure.

Hi Martin, thanks for the tips. BUT THERE WAS NO SILVER, ONLY BRASS PLATED IN RHODIUM.

 

[Martijn]

I misread that. Sorry. Then i have no idea what it can be. If it was bronze, it can be metastannic acid.

 

[diego Henrique vilela]

but your idea might be good

 

[Martijn]

If you look at the solubility chart, you see all nitrates (NO3 column) are soluble in water. Only gold and tin have a ? But tin creates tin paste.
If there was no chloride in the mix, i cant see another option than tin.
https://en.wikipedia.org/wiki/Solubility_chart

 

[Martijn]

If it is tin paste, i believe thorough rinsing, roasting to convert to tin oxide and dissolving in HCl is the recommended treatment for tin paste.

 

[diego Henrique vilela]

JUST to share with friends, I managed to separate the mud "chlorides" "hydroxides" that I had mentioned before, after washing it well I added sodium cyanide which cleaned it well and left the rhodium visible.

 

[hoytSmith]

I don’t see how you can get anything out of a metals in a nitric acid bath but nitrogen compounds and oxides (and chlorides & oxides for HCl). — and I see that the issue has been raised.

Rhodium-plated brass? That’s unusual as Rhodium plating is very hard and very thin: brass would start to show at the first scratch. Rhodium over silver is not uncommon, Rhodium over platinum is somewhat common, Rhodium over a base metal is confusing, although there have been periods where Rhodium has been relatively cheap compared to other PGMs. PGM over a base metal is common in electronics & electrical contacts, but Rhodium is good for chemical & heat resistance, it’s too brittle for electrical contactors.

Care to disclose your results? how much input material? what yeild/recovery?

I think that I would find a process to physically remove the rhodium plating before processing — preferably with an oxide that can be converted to a soluble chloride leaving the Rh plating as particles. Given the choice of dissolving base metals into soluble products & precipitating pgm’s from solution, I’d rather leave the pgms. The less base metal needed to be dissolved, the lower the cost of chemicals and less waste generated

 

[diego Henrique vilela]

I don’t see how you can get anything out of a metals in a nitric acid bath but nitrogen compounds and oxides (and chlorides & oxides for HCl). — and I see that the issue has been raised.

Rhodium-plated brass? That’s unusual as Rhodium plating is very hard and very thin: brass would start to show at the first scratch. Rhodium over silver is not uncommon, Rhodium over platinum is somewhat common, Rhodium over a base metal is confusing, although there have been periods where Rhodium has been relatively cheap compared to other PGMs. PGM over a base metal is common in electronics & electrical contacts, but Rhodium is good for chemical & heat resistance, it’s too brittle for electrical contactors.

Care to disclose your results? how much input material? what yeild/recovery?

I think that I would find a process to physically remove the rhodium plating before processing — preferably with an oxide that can be converted to a soluble chloride leaving the Rh plating as particles. Given the choice of dissolving base metals into soluble products & precipitating pgm’s from solution, I’d rather leave the pgms. The less base metal needed to be dissolved, the lower the cost of chemicals and less waste generated

I'm sorry friend, the least knowledge in Electroplating I imagined you had. the base piece is brass, then copper, then nickel, and lastly rhodium.

 

[diego Henrique vilela]

.Hello to all excellent members. I have a rhodium bath with 2 grams (rhso4) rhodium sulfate. I need to refine it to make it 99% pure. Does anyone have tips that can help me? Hugs and have a nice weekend.

 

[Yggdrasil]

.Hello to all excellent members. I have a rhodium bath with 2 grams (rhso4) rhodium sulfate. I need to refine it to make it 99% pure. Does anyone have tips that can help me? Hugs and have a nice weekend.

Is it a dirty/used bath?

 

[orvi]

I'm sorry friend, the least knowledge in Electroplating I imagined you had. the base piece is brass, then copper, then nickel, and lastly rhodium.

If this was your feed, than everything would nicely dissolve in nitric acid. Without any insoluble white pasty residue. Most obvious suspect is that base metal was indeed bronze, and you created metastannic acid.

If that was the case, I would probably try some other method to either dissolve base metal (like HCl based leach like AP or AR - rhodium won´t dissolve that well even in AR), or de-plate Rh from the surface using some electrochemical methods (simply put - reverse the electroplating as it is usually done and use plated stuff as anode).

 

[orvi]

.Hello to all excellent members. I have a rhodium bath with 2 grams (rhso4) rhodium sulfate. I need to refine it to make it 99% pure. Does anyone have tips that can help me? Hugs and have a nice weekend.

This would be quite a journey, considering the fact most of publically known Rh refining methods are very old, never complete and messy. Do you have any experience in refining of platinum group metals in general ? Because aside from Ir, Os and Ru, rhodium refining is probably most difficult one. But it depends on contaminants.
We do have reputable members here, which specialize on PGM refining and do it for the living, but I doubt they would share their proprietary methods with you.

If you intend to use the Rh to make fresh plating solution, this would need to be better than 99%, as for example slight copper contamination will ruin the quality of the plated surface.

 

[diego Henrique vilela]

Is it a dirty/used bath?

yes it is a 1 liter rhodium plating and contains 2 grams, but it has some impurities.

 

[diego Henrique vilela]

This would be quite a journey, considering the fact most of publically known Rh refining methods are very old, never complete and messy. Do you have any experience in refining of platinum group metals in general ? Because aside from Ir, Os and Ru, rhodium refining is probably most difficult one. But it depends on contaminants.
We do have reputable members here, which specialize on PGM refining and do it for the living, but I doubt they would share their proprietary methods with you.

If you intend to use the Rh to make fresh plating solution, this would need to be better than 99%, as for example slight copper contamination will ruin the quality of the plated surface.

I imagine that we are in a forum with the aim of helping all members, it has no aim to store information. Everything I know I share with friends... I'm not going to compete commercially with someone in Russia, Norway, USA... I'll simply solve my local problem.

 

[orvi]

I imagine that we are in a forum with the aim of helping all members, it has no aim to store information. Everything I know I share with friends... I'm not going to compete commercially with someone in Russia, Norway, USA... I'll simply solve my local problem.

This forum stores a lot of very useful and practical information. It is the most complex and most comprehensive PUBLICALLY AVAILABLE library of working, trusted methods on how to refine precious metals in the world. Check out Library section for example. And that is just a fraction of the information you can source here.

My questions were just general. Refining PGMs is very different from refining gold or silver, and I would say it is much more difficult for regular refiner to perform. My guess is, on this forum from many many members here, I would say maybe 10-15 people could perform the task you suggested cleanly, completely, with good recovery and present the Rh sulfate in sufficient purity to use it again.

This certainly could be done, and if you have all means, chemicals and PPE+hood, try it yourself. My point was just that do not expect the best results, as many (like myself) struggled a lot with Rh chemistry and refining.

 

[diego Henrique vilela]

Este fórum armazena muitas informações úteis e práticas. É a biblioteca mais complexa e abrangente, DISPONÍVEL PUBLICAMENTE, de métodos de trabalho confiáveis sobre como refinar metais preciosos no mundo. Confira a seção Biblioteca, por exemplo. E isso é apenas uma fração das informações que você pode obter aqui.

Minhas perguntas eram apenas gerais. O refino de PGMs é muito diferente do refino de ouro ou prata, e eu diria que é muito mais difícil de realizar para um refinador regular. Meu palpite é que, neste fórum de muitos membros aqui, eu diria que talvez 10 a 15 pessoas poderiam realizar a tarefa que você sugeriu de forma limpa, completa, com boa recuperação e apresentar o sulfato de Rh com pureza suficiente para usá-lo novamente.

Isto certamente poderia ser feito, e se você tiver todos os meios, produtos químicos e EPI + capuz, experimente você mesmo. O que quero dizer é que não espere os melhores resultados, pois muitos (como eu) lutaram muito com a química e o refinamento do Rh.