precipitating rhodium

[Geo]

i have the opportunity to reclaim rhodium from some dirty plating solution. according to the jeweler, each pint contains 1g rhodium. he estimates 1/4g may have been used from each pint. there are 7 pints. i tried to search for the process and came up with many thousands of hits for each part of the search. i need to know what compound or chemical i need to precipitate the rhodium as clean as possible.

 

[butcher]

I rarely get a chance to work with this metal so others advice may be better.

I would use zinc, this would precipitate every thing below zinc, the other metals can be removed from the cemented powders, since my guess at this point is that the plating solution is sulfate based, the cemented Rhodium would be converted to elemental metal powders and no longer a water soluble rhodium sulfate compound, a neutralizing wash with a solution of sodium hydroxide, so then the powders would form a water soluble sodium sulfate solution Na2SO4, this can also help to form oxides and hydroxides of most of the cemented base metals.

My idea here is to try and get rid of as much sulfates from the cemented powders as possible as a fusion with sulfates could make Rhodium water soluble again, which would not be good when trying to remove the other base metals.

Rinse the powders well to try and remove the soluble sodium sulfate.
Dry with slow heat and raise temperature to incinerate the powders, cool and give them a rinse in water, nitric acid can be used to remove the other base metals, more rinsing and drying the powders can then be sold to a refiner.

You can try to process the Rhodium by a sulfate fusion or some other method but with the difficulty of the process you may get more from them by selling them.

 

[Geo]

thank you Butcher. actually, the material belongs to a local jeweler that im trying to add to my costumer list. he seems to be interested in letting me refine his sweeps and buffing and polishing materials. he mentioned a couple of rugs as well. i would like to impress the man as much as i can. he already has tested a couple of samples of my refined gold and is willing to work with me on a 24 Karat level. this could be the first of many, if i can make a good impression on this man.

 

[goldsilverpro]

At a large refiner I worked for a long time ago, we used magnesium powder to precipitate Rh from plating solutions. Since we then shipped the sludge back to the home office for processing, I don't know the next steps. I do think the excess Mg is soluble in most mineral acids (HCl, H2SO4, HNO3, etc.). However, since there's a lot of free acid (usually H2SO4) in the plating solution, it may dissolve the excess, unless you add way too much. I don't know why Zn wasn't used. Maybe the Mg produces a cleaner product and/or a more complete precipitation. It shouldn't take much - theoretically, I would say about 1/3 to 1/2 of the rhodium weight. In practice, that might be different. I would guess that the solution color would fade to water clear when all the Rh is out. I would add it in small increments with stirring. Experiment with a small amount of the solution first.

If you use Mg, read up on it before using it. It can easily ignite under certain conditions.
http://www.magnesium.com/w3/data-bank/index.php?mgw=222
http://www.ebay.com/sch/?_nkw=magnesium%20powder&clk_rvr_id=399100928240

 

[freechemist]

Hi Geo,

Recover and refine rhodium is really a bitch, - an so are rhodium-market and -pricing: highly intransparent and sometimes even clandestine. Rhodium pricing is prone to sudden and drastic changes over very short time-periods, compared to different PM-pricing. Today rhodium is valued lower than gold and/or platinum, but this has been very different in the not too far past, and probably will change in a not too far future, abruptly and drastically. Therefor, the only advice I can give you is, to try to build up a relationship based on mutual confidence with your hoped for customer, offering him the services to recover raw rhodium-metal out of his used up plating baths and to care about the remaining wastes (diluted sulfuric or phosphoric acid, dissolved salts and additives). In my practice, cementation with zinc-dust, added in small increments, with constant stirring, was the way to go. After sedimentation, the precipitate was filtered, washed with plenty of water, taken up in 1M HCl and boiled for about 1 hour, to dissolve some remaining zinc, washed again with water, dried and calcined at 600-800oC, giving raw rhodium-powder of an average content of ca. 85%Rh. This could be collected and given to an external refiner from time to time, or, optimally, back to the producer of the plating baths, who eventually will take in account your rhodium and supply you with fresh bath or concentrate to prepare new baths.

Good luck, freechemist

 

[Geo]

thank you freechemist for the advice. the jeweler would like the Rhodium metal as clean as possible and wishes to pay me my percentage in cash on metal weight. this is acceptable to me as i have no need of the metal.