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

[HAuCl4]

The insolubles filtered off are fused at 500 C with molten sodium bisulfate. This converts the Rhodium to water soluble Rh2(SO4)3 . The Ru, Os, and Ir are untouched. The sulfate cake is cooled and dissolved in water, the insolubles filtered off and the Rhodium is precipitated with NaOH and collected for further purification as quantities warrant.

The remaining insolubles are fused with sodium peroxide and sodium hydroxide at 500 C forming water soluble sodium hyperosmate and sodium ruthenate. The iridium is now Iridium dioxide.
The iridium dioxide is dissolved in aqua regia and precipitated as ammonium hexachloroiridiate with ammonium chloride. The salt is further purified by digestion in dilute ammonium sulfide which will precipitate impurities filtered and re-precipitated with ammonium chloride to reform the ammonium hexachloroiridiate. This can be reduced in hydrogen at 1000 C to pure metal.

What are the processes used industrially to re-purify to obtain high purity Rhodium and Iridium after they are in solution as sulfate for Rh, and as chloride for Ir?. What is the standard for high purity in these rare metals?.

As you can see I'm getting very little gold and silver to refine these days, and I'm confined to research and study!. :lol:

 

[Lou]

Dude, who do you work for? :mrgreen:


Ir and Rh are notoriously difficult to separate, and almost impossible if they're in the trivalent state. Ir is the most challenging of the platinum group metals to refine, and almost everything about Ir and Rh chemistry is strictly proprietary. Which means that no one will really give you the goods.

So, options on refining? 4metals listed the classical method for Ir but it's not terribly satisfactory--usually it's followed up with SSX. Fusion is about the only way to to get Ir into solution, although you can make Na2IrCl6 (and the same thing with Rh, but valence +3) by heating it in a fast stream of chlorine with NaCl matrix and then digesting it all in dilute HCl. You can get rid of some of the earlier base metals with hydrolytic separation (pH controlled).

Rhodium, oh rhodium--many ways here. Ammonium hexachlororhodate isn't nearly as insoluble as the hexachloroplatinates and " "palladate congeners. Furthermore, it's more prone to include base metals as it crystallizes. Typically, the ASHs (the nitrite salt) are one manner in which it's done, but again, solvent extraction works a charm by removing contaminants from the Rh The big rider with rhodium is usually iridium, thankfully, one can oxidize Ir to (IV) in acidic milieu and selectively pull out the Ir and strip with dilute HCl. Or you can electrowin it. Anyway, there are organic precipitants that are usable too.

I'm not surprised you haven't turned anything up in the literature.

I have some pure 3N5 Ir and pure Rh, if you want to try your hand at it. I can sell you an ounce of each and you can chase them through solution if you like...

 

[4metals]

Chloride,

I really haven't spent a lot of time with PM's other than Gold, Silver, Platinum, and Palladium. Now if I was well versed in Iridium and Rhodium as well I might have chosen the name 6metals.

At todays prices, I'd suggest you fork over $3330 to Lou and have at it. :lol:

 

[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:

 

[HAuCl4]

Chloride,

I really haven't spent a lot of time with PM's other than Gold, Silver, Platinum, and Palladium. Now if I was well versed in Iridium and Rhodium as well I might have chosen the name 6metals.

At todays prices, I'd suggest you fork over $3330 to Lou and have at it. :lol:

I resent your name calling. I'm not a salt, I'm an acid. Respect please!. :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

 

[HAuCl4]

Thanks Lou. Makes sense too. Cheers. 8)

 

[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.

 

[Davidoro]

Does anyone know of a refinery in US that has "closed loop chlorine gas separation" process smelter/Refinery :G