# Sequence of Precipitation for all PM in AR



## relpub3 (Aug 27, 2007)

Hi, I have read somewhere that the best sequence for precipitating precious metals would be as follows in an aqua regia solution containing palladium, platinum, rhodium, other minor platinum sisters, silver and gold. Assuming that all metals are in such fine powder form so that dissolution of silver will not form an impenetrable silver chloride shell.

1. Use hot AR to dissolve all that can dissolve. 

silver would be be undissolved as silver chloride so it is a matter of filtering it out. Unfortunately the other platinum sisters such as iridium, ruthenium and osmium would not dissolve in the AR and would be there with the silver when it is filtered out.

Use ammonia to dissolve the silver chloride so that what remains are the undissolved platinum sisters. Filter these out and set aside for sending to a refinery that will take these items.

2. Add ammonium chloride to the hot concentrated AR to precipitate the platinum as orange powder. Filter powder out.

3. While AR is still hot, add sodium chlorate to precipitate palladiium also as an orange powder. Filter powder out.

4. Let this solution stand undisturbed for at least 24 hours to let rhodium precipitate out by itself. Disturbing the solution might prevent the rhodium from precipitating out. Filter any rhodium that precipitates.

5. Add urea to the AR to destroy the remaining nitric in the AR and then use SMB to precipitate the gold.

6. There, all precious metals are accounted for ready for further processing (esp. the platinum, palladium and rhodium).

Question:

Anyone commenting if this procedure works as described, i.e. are there any other steps that should be done in the sequence?

Thanks

Alberto


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## Harold_V (Aug 28, 2007)

I never used heat for precipitating platinum. It was always accomplished at room temperature. A saturated solution of ammonium chloride was introduced to the AR solution, which was always evaporated to expel nitric prior to any attempt at recovering any of the values. When the ammonium chloride was introduced to the filtered solution, there was an instant cloud of platinum salts. Any iridium present was included in the platinum----I made no attempt at separating the two. 

Sequence should be dictated by the amount present-----in my case it was almost always gold first. You have no choice with palladium and platinum---the first operation for palladium is the same one for platinum, although you don't get clean precipitation by these methods. There's always traces of all of the metals on first precipitation, which stands to reason. 

Harold


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