# Rhodium plating refining



## Anonymous (Nov 28, 2007)

*  Hi
I have 10l old rhodium plating.
I am looking for any info. regarding refining rhodium plating.
Thank you
Mati :evil: *


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## Lou (Dec 1, 2007)

Might want to boil it down to concentrate it as much as possible. 

Do you have a brand name for the plating solution?

If it's spent Rh solution, you probably won't have much Rh in there. There's usually a bunch of organics and various chemicals in there to improve the finish. I'd probably heat it to red heat to burn off all of the organics, then heat it some more until the rhodium sulfate decomposes to rhodium oxide. Then dissolve all the mixed oxides in HCl and precipitate as many of the base metals (shouldn't be that many) away until I have RhCl3 solution. That's reducible with N2H4/hydrazine or you can do it cleanly with hydrogen at about 900F to give you rhodium sponge. Should sell for about 90% of spot. That's just how I'd try for it.

I'd hope that goldsilverpro weighs in on this one since he's got some serious experience with plating solutions and can probably tell you better what would be in there and how to proceed than I could. Only rhodium I ever dealt with came as either crude sponge material, or was a high purity salt that just needed reduced to metal.

Lou


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## Lino1406 (Dec 1, 2007)

You can add magnesium powder
to Rh solution and get the rhodium
sponge at once.


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## goldsilverpro (Dec 1, 2007)

It's been about 35 years since I recovered the rhodium from plating solutions. At that time, a company I worked for, in L.A., formulated and sold several different types. I would imagine that the formulas are the same today. Here's what I remember.

We sold two different strengths. For industrial or electronic applications, there was a 5 gm/liter rhodium solution. For jewelry uses, the solution was 2 gm/liter of rhodium. The stronger solution allowed for thicker deposits and was used for such things as PCB fingers or memory disks. 

By far, the most common solution was made up with rhodium sulfate and sulfuric acid. If I remember right, there were no other additives. Another formula (I think this is right) used rhodium phosphate and phosphoric acid. Here again, I seem to remember that there were no additives used.

The L.A. facility where I worked also had very large gold refinery, but we didn't do any PGM refining there. Before doing anything, we would determine the quantity of rhodium in the solution, using atomic absorption or precipitation. We would then precipitate the rhodium as metal powder, using a cementation method, and ship the powder to our N.J. facility for refining. Here's where my memory fails me. I'm thinking we used zinc dust to precipitate the rhodium but, I'm also thinking we may have used magnesium to drop it. 

If the solution you have is unused, you could have about $4,000 to $10,000 worth of rhodium, depending on the initial make-up. If the solution has been used, it could be worth far less. The solution color is an indication of the value. Rhodium sulfate is a red-brown color. In general, the darker the solution is, the higher the value.

As an amateur, I wouldn't try to refine the rhodium yourself, considering the potential value. It's a very complicated method, requiring special equipment, and the odds are that you would lose much of the value.

Your best bet is to sell it to a refiner. I would pick a big one that specializes in PGM, such as Matthey Bishop - they are all over the world. However, before doing this, you must plan carefully and not do anything that would diminish the value of the material. 

You must determine the rhodium content before selling it. Otherwise you're leaving yourself wide open. The best scenario would be that the solution is in sealed (by the manufacturer) bottles. If this is the case and, if there is a label on the bottles, don't open them. The rhodium content should be listed on the label. If not, contact the manufacturer and ask them the rhodium content. 

More likely, the solution is not in sealed bottles. If not, I would combine the solutions together, mix well, remove about a 20 mL sample, and put it in a small, clean, dry plastic bottle. One way to get the solution analyzed is to call around and find a lab with an atomic absorption (AA) unit. They must have a rhodium lamp for the AA. Pay to have them analyze the rhodium content. There are more accurate methods for analyzing the rhodium but, they will be more expensive. Probably the most accurate way is to precipitate the rhodium, as metal, from a 5 mL sample, using zinc or magnesium. The excess Zn or Mg can be removed with weak HCl or H2SO4. If the solution was contaminated with other metals, they will be mixed in with the powder and will also have to be leached out. When all the Rh has dropped, the solution should be pretty much water clear. After rinsing, drying, and weighing the powder, the Rh content of the main solution will be known. I wouldn't do this yourself unless you are a chemist and have a well equipped lab. Let a commercial lab do it.

Once you know what you have, I would take all the solution to the PGM refiner. I would have the refiner take a sample, give half of it to you, and then have him seal the main solution with a numbered seal, so it can't be tampered with. If the refiner agrees, I would take the solution home with me. When he finishes analyzing his sample, you can decide whether or not you want to sell it to him. If you don't like his numbers, take the solution elsewhere.

All in all, I would definitely sell it in solution form. Solutions have a very low gray area. They are homogeneous and are easy to sample. I would NOT treat the solution and try to sell the solids. You would then have a material with a very large gray area.

These are just some ideas. I could make more specific recommendations if you would give much more detail about what you have.


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