Separation and Purification Au,Pt,Pd,Ag,Rh,Os,Ir,Ru

[HAuCl4]

For now I have a purely academical interest in those two metals. I haven't even read the old Gilchrist and other papers about them. :shock:

I also have an old beef against Johnson Matthey and Co. :lol:

 

[Lou]

I can give you Raleigh's work. It's not how it's presently done, but it does work!

 

[HAuCl4]

I can give you Raleigh's work. It's not how it's presently done, but it does work!

8) . Let me find the titles of 2 or 3 I'm interested in reading. He has too much stuff published. Or you can suggest!. Thanks in advance.

I'm mostly interested in iterative processes, like what you posted about melting silver nitrate and washing with distilled water, and re-crystallizing, etc. Simple methods that produce lots of 999999s with repetition and little waste!. :lol:

edited to add: Shall I PM you with the 3 old papers I'd like to read?. If I find a procedure improvement, I'll post it in the open right here, but there may be restrictions on posting scientific papers.

 

[HAuCl4]

This is the list of papers I sent to Lou, if anyone else is interested:

1-New Procedure for the analysis of dental gold alloys. Gilchrist. 1938.
2-Assaying platinum metals. Schwitter. 1932.
3-Purification of the six platinum metals. Wichers, Gilchrist and Swanger. 1928.
4-Refining and melting some platinum metals. Whiteley and Dietz. 1928.

I already have the Wichers and Gilchrist paper: A procedure for the separation of the six platinum metals from one another and for their gravimetric determination.

Also if you have the very old 1878 french paper by Deville and Stas discussing the making of the Kilogram and Meter in Pt-Ir alloy, I'm sure I'll enjoy reading it too.

Cheers.

edit to add: It seems to me that the biggest complicator and promoter of mistery and secrecy was the Devil-le when he introduced ammonium chloride to refining!. Everybody else that followed seems to have spent their lives cleaning up that mess!. :lol:

 

[HAuCl4]

Here's a crash course in PGM refining. Learn to melt them and you are nearly there!.:lol:

 

[HAuCl4]

How much % of Pt goes into solution when one subjects a mix of Pt, Pd and Rh blacks to sulphuric acid?.

How about to fusion with NaHSO4 ?.

I'm experimenting for total dissolution of Rh and Pd and minimal dissolution of Pt, before further processing, but it'd be nice to know the theoretical expectation. :shock:

 

[Lou]

Less than half a percent. It is really contingent on how pure your bisulfate/pyrosulfate is; if it has much chloride in it, then much more Pt will be oxidized.

Lou

 

[freechemist]

Chloride content of a bisulfate/pyrosulfate fusion-mixture may indeed be critical, regarding Pt-oxidation. Also it is very important if you work with bisulfate (KHSO4) or pyrosulfate (K2S2O7). On melting your metal-black mixture with bisulfate you probably are on the lucky side, because chloride in your bisulfate melt will quickly be volatilized as HCl-gas. In contrary, working with pyrosulfate containing much chloride impurities, which contains no acidic protons, makes the formation and volatilization of gaseous HCl impossible, therefor resulting in a more aggressive melt, oxidizing more platinum through formation of potassium-hexachloro-platinate(IV) (K2PtCl6) in the fusion mixture.

freechemist

 

[HAuCl4]

Thanks freechemist. So it follows that pre-fusing the bi-sulphate alone, with say a little zinc, would gas-off all the contaminating chlorides, and using that pre-fused bi-sulphate on the blacks would dissolve very little platinum, if any?.

Also what is the advantage of potassium versus sodium bi-sulphate?. :?:

 

[Lou]

It works better.

No zinc is needed. Simply heating the KHSO4 will cause any HCl present to leave, as it is a volatile gas that may be removed from the equilibrium.

 

[HAuCl4]

Thanks Lou. Conversely a well formulated mix should put all the 3 metals in solution with just one fusion?. :idea:

 

[Lou]

I suppose it is possible if one adds NaCl to the mixture, but generally speaking, it's best to avoid halides and heating platinum metal, due to the risk of disproportionation and gas phase transport of values.


Lou

 

[freechemist]

It is possible, to bring all three metals into a soluble form by means of a pyrosulfate/NaCl-mixed melt. With K2S2O7 only sparingly soluble K2PtCl6 is obtained. No platinum is volatilized as PtCl4 because it will remain in the melt as the non volatile anionic complex PtCl6(2-). The mixed salt melt itself at reaction temperature (500-550oC) is not stable, and will decompose in a few hours, probably loosing SO2Cl2 (sulfuryl-chloride) as a volatile gaseous compound and/or by loss of gaseous SO3 (sulfur-trioxide). This can well be understood, regarding the pyrosulfate-anion S2O7(2-) as the addition product of sulfate SO4(2-) and one mole of SO3, which is the active oxidant in these fusion mixtures, being reduced to gaseous SO2 in course of the solubilization reaction.

freechemist

 

[HAuCl4]

Thanks freechemist and Lou for your guidance.

I have now proved to myself that fusion with pre-fused NaHSO4 is an extremely clean separation of the "upper" Ag, Pd, Rh, from the "lower" Au, Pt, Ir. This should lead to more expedite clean separations of the 6 metals in combination (yet to be tested).

I want to test next some cat extractions with the mix freechemist suggested of NaCl and Pyrosulphate to see how complete the leaching is.

 

[4metals]

The moderators would like to thank all of the members that contributed to the original thread upon which this thread was based, as well as those that asked questions showing what was missing. Because of the extra length and interest in this thread we have created the above consolidated version making for an easier read. We encourage all members to read, comment, and ask questions in the original thread, Separation and Purification of Au,Pt,Pd,Ag,Rh,Os,Ir,Ru

The Library threads should not be considered to constitute a complete education. Instead, they're more like reading a single book on the subject of recovery and refining. There is so much more information on the forum, and it is impossible to include it all in these condensed threads. Members are strongly encouraged to read the rest of the forum to round out their education.