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



## 4metals (Feb 21, 2010)

These methods are to process concentrates and are usually not worth processing small quantities. The details have been left out for the Ruthenium and Osmium as these are really dangerous metals and should only be handled in closed reactors. 

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

This is a general schematic for processing a concentrate of any combination of the above listed metals usually generated from anode slimes or slimes collected from cementation of waste acids holding values.

Roast the slimes to convert any PdO to metal to assure its place in the soluble fraction. 

The concentrate is treated in aqua regia, this solubilizes the gold, platinum and palladium and leaves the other metals in insoluble form. 

The solution basically contains HAuCl4, H2PtCl6, H2PdCl4. Drive off the NOx by classic boil down and successive 3X’s addition of HCl. Drop the gold with either Sulfur dioxide or Ferrous sulfate. It has been suggested that reducing the gold with Ferrous sulfate results in a more complete drop of the platinum in the following steps. Gold, with either precipitant, will have to be re-refined for high purity. Alternatively the gold can be extracted with Dibutyl carbitol and recovered with oxalic acid resulting in a high purity gold and leaving the Platinum and Palladium behind for recovery. 

The Pt is dropped by treatment with Ammonium chloride to drop the insoluble (NH4)2PtCl6. These salts are washed with a solution of 15% ammonium chloride and dried. The salts are collected and further purified via bromate hydrolysis. 

Pd is dropped with a solution of dimethylglyoxime dissolved in dimethyl sulfoxide. The yellow palladium glyoxime is filtered and washed with 60% alcohol and 10% HCl. The alcohol assists in the drying and the dry palladium glyoxime is dissolved in excess ammonium hydroxide until dissolved and generating a clear solution. The addition of HCl results in the precipitation of diaminopalladous chloride salt or “palladium yellow” 

You have now completed the easy part, the following treatment is for the insolubles left behind in the aqua regia process. 

The insolubles are smelted with lead carbonate, carbon, borax and soda ash. This forms a slag with silica, alumina and base metal impurities. The PM’s are dissolved in the lead. Separate the lead and the slag, remelt the lead and granulate it in nitric acid. Filter off the insolubles, Rh, Ru, Ir, and Os.

The silver and lead are in the Nitric acid, sulfuric acid is added to drop out the lead as insoluble lead sulfate. This is collected and converted to lead carbonate and recycled. Classically the silver is dropped as a chloride and smelted but cementation with copper yields an effective product for further electrolytic purification. 

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.


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## nickvc (Feb 22, 2010)

Now thats a post 4metals 8) ,but im glad i dont handle enough Pgms to make it necessary im sure i would end in a right mess :lol:


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## Irons (Feb 22, 2010)

Good information.

4Metals, What is the cost benefit to using DMG?

A note to those contemplating trying this with 'ores' and concentrates: Always assume Arsenic and probably Selenium are present and will become volatile when digested in AR. Native materials should always be digested in a sealed system with provisions to collect the fumes.
Even AP can volatilize Ruthenium in 'ores'. It's not an effective recovery technique but it's enough to make you very ill.


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## golddie (Feb 22, 2010)

> Alternatively the gold can be extracted with Dibutyl carbitol and recovered with oxalic acid resulting in a high purity gold and leaving the Platinum and Palladium behind for recovery.


Hi 4metals
How is this done
extracted with Dibutyl carbitol

do you precipitate the gold in AR with Dibutyl carbitol 
also what do you mean recovered with oxalic acid


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## 4metals (Feb 22, 2010)

Irons,

The cost benefit to DMG is a question of scale. I always ran jewelry related materials so the Pd rarely exceeded 10% of the Pt content. DMG was quick and provided a way to store the Pd as Pd glyoxime until I had enough to purify fully. The alternative could have been sodium chlorate. 

Goldie,

Methods of dibutyl carbitol extraction have been posted on this forum before. I'm not trying to be mean so don't take this the wrong way but these techniques require a pretty good grasp on the chemistry involved. The last thing I want to see is someone hurting themselves. If you are interested in solvent extraction, try it on small lots with known contents. Extraction is selective and does not carry over PGM's so subsequent PGM recovery is simplified. Read the posts about it and be careful.


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## Irons (Feb 22, 2010)

And do it outdoors. It smells like the oxidized funk of something you wouldn't want to meet in a dark alley.


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## Lou (Feb 23, 2010)

I try and keep away from DMG, it's too expensive. Under the right circumstances, it's definitely a very selective precipitant. Unfortunately, the voluminous precipitate it makes with Pd is quite likely to drag down other impurities in solution. I suppose if you're doing small amounts of Pd it's worth the money...


Good work leaving the oxides of Os and Ru out of it--many are ill equipped to deal with them. That and the metals are so very rarely encountered (especially osmium; ruthenium is used as a hardener in some jewelery platinum alloys).


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## Harold_V (Feb 24, 2010)

My opinion is that it is an excellent indicator, but using it for recovery of palladium borders on the ridiculous. Not only is the volume excessive, the resulting solid material is akin to working with grease. However, it really shines when you have doubts about the results of a stannous test. I routinely used a combination of ferrous sulfate, DMG and stannous chloride when testing mixed elements. Quite a common occurrence when refining jeweler's wastes. 

Harold


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## butcher (Feb 24, 2010)

Note caution: 
The details have been left out for the Ruthenium and Osmium as these are really dangerous metals and should only be handled in closed reactors. 

$Metals :thanks for going through that, we know you are a busy man.


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## Irons (Feb 24, 2010)

..and Ruthenium Tetroxide detonates at 109 Deg. C. I was near a fume hood when some Ruthenium Tetroxide we were distilling detonated. It wrecked the hood and contaminated the lab. It was a very expensive accident. That was my first introduction to Ruthenium poisoning.


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## One Blanket (Apr 27, 2010)

Hello all, 
I have an ore that will wait until who-knows-when-if ever for any attempt at progress.

I have two assay reports that differ and will wait ( forego the expense ) before getting any more.
Our member Richard36 says Fe Pd Ru Ir almost no Au or Silver
a hand held ? Niton ? ?xrf analyser says 96% Fe 2.7% Ir

PGMs appear to me to be too hard to recover for any expectation of profit at this point if ever 
If anyone wants some to play with i can pay the freight.


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## shyknee (Apr 27, 2010)

can someone let me know if i can use potassium chlorate to precipitate palladium 

and or if there are any drawbacks if it is usable .or special procedure 

thanks


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## Lou (Apr 28, 2010)

It works, but not nearly as well as sodium chlorate. You're better of using sodium hypochlorite (bleach) in lieu of KClO3.


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## shyknee (Apr 28, 2010)

thanks Lou

what shall i do to dispose of the potassium chlorate about 300grams or so

and I don't want to build a rocket or smoke up the neighborhood ? :|


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## lazersteve (Apr 28, 2010)

Lou said:


> It works, but not nearly as well as sodium chlorate. You're better of using sodium hypochlorite (bleach) in lieu of KClO3.



I'd also like to add that calcium hypochlorite (dry bleaching powder) also works as does most any source of chlorine gas.

Steve


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## Lou (Apr 28, 2010)

I wouldn't get rid of it! You can make a solution of KClO3 in hot water and add this solution to gold that is sitting in HCl, it'll put the gold into solution right quick!

Then you can reduce with bisulfite or all the usual suspects insofar as reducing agents go.


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## shyknee (Apr 29, 2010)

thanks Lou
I will have to try this 
everyone hates to wait.

humm :?: :?: would it put palladium that is siting in HCl into solution faster :?:


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## Lou (Apr 29, 2010)

Yes, it will also dissolve palladium quickly too.

Just keep it away from platinum.


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## HAuCl4 (Aug 23, 2010)

4metals said:


> The salts are collected and further purified via bromate hydrolysis.



Would you please ellaborate on this re-purification?.

After this "bromate drop", what is the best way to get the pure platinum out of solution and then reduced to metal with minimal losses?. Fire or formic acid?.

How to assay the purity of the platinum and palladium final product?. Can one expect 999+ or maybe 9999+ Platinum?. How about Palladium fineness?.

Let's assume the other PGM metals are just kept together as mixed powders in very small quantities, if any, and just focus on the Pt and Pd, that were mainly dropped from a gold chloride solution with ammonium chloride, and sodium chlorate, before dropping the gold.

In summary the "feed" for re-purification are the colored salts of platinum and palladium, separate or mixed, containing traces of other PGMs. And the goal is high purity Pt and Pd, with minimal losses and hassle.

Thanks 4metals, Lou, others, in advance.


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## 4metals (Aug 23, 2010)

A bromate hydrolysis was discussed and described in detail in this thread. 

http://goldrefiningforum.com/phpBB3...=6200&p=54384&hilit=bromate+hydrolysis#p54384

Reduction of the resulting salt can be accomplished using hydrazine or by using a tube furnace with a hydrogen atmosphere, which has been discussed by Lou as well.

http://goldrefiningforum.com/phpBB3/viewtopic.php?f=49&t=7458


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## HAuCl4 (Aug 24, 2010)

Those two threads are awesome and full of useful, hard to find, information.

Would you guys mind if I compile several of those threads, and other book, articles, etc. content into one coherent, step by step document to refine silver, gold, platinum and palladium in a straightforward and expedite (one day refining) manner? . Let's leave the "other" metals out as black residues for now.

It may take me a while to post a document ready to be commented/edited/etc by other members, but I feel it would be a worthwhile contribution to "get it all in one place". My only contribution would be to assemble the processes that have been shared by others, and even that may be re-assembled better if a reasonable "better way to do things" is pointed out.

I feel the need to ask permission, since some of the work and experienced steps shared by Lou, 4metals, Lazersteve, GSP and others, could be considered "proprietary". It has been made public in one way or another...but still...

Game?. :?:


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## Oz (Aug 24, 2010)

I would be hesitant as there are some advantages to new people having to put this information together piece by piece themselves while learning on the forum. It slows them up just enough to learn safety as well as what “not” to do before they find out the hard way. Unless you are writing a book it is also hard to cover all the variables that occur based on the feedstock, each requiring a different approach. 

Are you proposing writing a book based on the forum? I am unsure how involved you intended this to be, but appreciate your intent. Ultimately every word written here is the property of Noxx, the owner of the forum. 

You asked so I know this is not your intent, but in the past we have had people lift/steal processes and procedures word for word and sell them as their own work, one guy was actually selling a rather complete copy of the forum on fleabay. Putting everything into a book format makes theft a bit too easy for someone using cut, copy, and paste and selling it as their own work on fleabay or elsewhere. 

Just a couple thoughts.


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## HAuCl4 (Aug 24, 2010)

It would be a 4-5 page document of step-by-step procedures, posted publically for the original contributors to dissect/correct, etc. 

Only if the original posters give their permission, and OK.

The thought of writing a book crossed my mind, but I have decided to pass because frankly I'm not qualified, and there are others better at this than me, with tons more practical experience, and it's other's people content. What I would be contributing of my own is really a minute portion, especially since there are "better ways" that I learned right here.

I'm compiling a document for myself anyway, and again, will not post unless everyone involved is OK. It'll take a while.


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## Oz (Aug 24, 2010)

At 4-5 pages I would imagine you plan on outlining the procedures for these metals from a scrap jewelry feedstock perspective. I can see some value in that.

There are indeed several members more than qualified to write a book based on their own experience. In fact our own Goldsilverpro has http://goldrefiningforum.com/phpBB3/viewtopic.php?f=84&t=5810&hilit=book


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## Lou (Aug 24, 2010)

I expressly grant my permission for anyone to use what I've said here for commercial gains so long as they agree to a.) indemnify and hold me harmless for any (mis)use of any procedure, methodology, technique, or idea I've outlined or espoused, b.) credit this forum and myself. What I state by PM is a different story--I'd rather have people NOT post that, forward it, or disclose it without my express written permission. 


Time willing, I'll get all the photographs together for my book on techniques of purifying and assaying the platinum group--it focuses mainly on higher end scrap and relatively pure commercial feedstock, but I also will cover S/X on each of the PGMs. So far it is review-style and HEAVILY referenced (several hundred articles, technical pubs, patents). I really need to pare it down...who would want to read an 800 page treatise on the latest and greatest in processing PGMs? I'd really like to add an escrap and karat gold section, but karat gold books are a dime a dozen. Also, it is quite biased to my personal whims, which should be removed or at least moderated.


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## HAuCl4 (Aug 24, 2010)

On a better light: I think I will just compile the document for myself, and if anyone is interested they can look on the posts and threads of their interest and do the same. I don't want to ruffle any feathers.


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## 4metals (Aug 24, 2010)

I tend to agree with Oz on this issue, while I have no issue with someone compiling the procedures discussed here, the methods involved in these particular threads involve a higher degree of understanding of chemistry. Those members who wish to follow the threads and develop useful methods for their own circumstances usually have enough knowledge to follow the threads and ask questions when necessary.

By summarizing these threads you make it easier for the more casual refiners to just jump in and possibly hurt themselves. I do not think that would be wise. 

Some of the discussions here have been put together, I believe by Palladium, (or is it Gold, or Platinum or all of the above?) but those discussions were not of this threads nature. 

Harold has put together an excellent collection of methodology that he used in processing at his refinery. His descriptions were written to be easily understood by those with less chemical background and have helped many on this forum. 

Ultimately what you do is up to you, but if you read some of the posts that are made here you can understand the benefit of having a member do his or her homework, or due diligence, before beginning to process the more challenging metals.


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## nickvc (Aug 25, 2010)

HAuCl4 I don't think your ruffling any one who has been posting on this thread most of the members commenting understand what is been discussed but their concerns over new members who just leap into processes they don't understand I feel is well justified. Your knowledge of refining is well documented as are all the others commenting but read the threads from new members and I think you will see why there are reservations. I refined commercially for many years but my original comment on this post still stands, my actions concerning PGMs is going to be the same as ever , melt assay and trade to some one who knows their way round them and for the vast majority of the members that's the best and safest way.


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## HAuCl4 (Aug 25, 2010)

It's settled: It's better to not do what I proposed. Better men for the job to write a book or procedures that will hardly be used by anyone anyway. No harm done or intended either way.

Back to PGM: In page 205 Hoke quotes Wichers:

"A second precipitation of the dioxides suffices to effect complete removal of platinum". (After referring to the dioxides after the bromate hidrolysis in 2 lines!).

How do they put that stuff in solution again to repeat the bromate drop?.

How to assess the purity of the Platinum after going through all this?.


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## HAuCl4 (Aug 25, 2010)

One last question, before I go away from the computer for a while:

Let's say from a mainly gold solution with excess sodium chlorate, I recover both the palladium salts and the platinum salts together with ammonium chloride, before processing the gold. 

I save the mixed salts till there is a large enough amount that merits processing. 

What is the best plan forward if I want to produce very pure metals Pt and Pd?.


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## HAuCl4 (Aug 26, 2010)

After more reading...

1-Would a thorough wash with ammonia dissolve most of the palladium salts and silver chloride and leave the now relatively clean platinum salts as solids ready for the "bromate hydrolysis" process with the goal of pure platinum or would it be better to reduce to metal and re-dissolve, etc. before attempting the "bromate hydrolysis"?.

2-Is there a direct way to directly precipitate Pt with some other precipitant, after the "bromate hydrolysis" that avoids dropping the Pt with ammonium chloride before reduction to pure metal?.

3-What to do with the palladium+silver+other solution from 1 to get to pure palladium?. Reduction to metal, re-dissolve in A.R. and DMG to get very pure palladium or is there a way to avoid the cumbersome DMG and still get very pure palladium?.

Thanks for answers in advance.


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## HAuCl4 (Aug 27, 2010)

HAuCl4 said:


> 2-Is there a direct way to directly precipitate Pt with some other precipitant, after the "bromate hydrolysis" that avoids dropping the Pt with ammonium chloride before reduction to pure metal?.



Would it be a complete mistake to drop the Pt with copper after the bromate hydrolysis or the contamination to the final product would be too great?.


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## HAuCl4 (Aug 27, 2010)

Is there some process similar to the Platinum Bromate Hydrolysis, but to purify Palladium from other PGMs?.

Talking to myself like the lunatics?. :lol:


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## 4metals (Aug 27, 2010)

This procedure will clean up Palladium which have been collected as salt and reduced.

It is useful to separate Pd from Ag.


•	Refining Palladium concentrates. 

•	Digest the impure palladium metal in 50% nitric / distilled water.

•	Raise the pH to anywhere between 1 and 2 with NH4OH

•	Filter the solution to remove any turbidity or sediment, which may be AgCl.

•	Take a volume of solution equivalent to 500 grams of palladium.

•	While stirring add NH4OH to a pH of 10 (Expect to add at least 1500 ml of NH4OH) Any Iron or Nickel will precipitate.

•	Filter the solution of any turbidity or sediment. 

•	Acidify with HCl to pH 6.5 to 7. At this pH any AgCl will come out of solution. 

•	Filter the solution to remove any sediment. 

•	Continue to acidify with HCl to a pH of 3 where the precipitation of Palladium is essentially complete. 

•	Cool the batch and decant or pump off the liquid. Slurry the precipitate to a buchner funnel and rinse with a rinse liquid made with 10 ml of HCl per liter of DI water. 

•	Place all liquors into reclaim as there are always values which should be cemented and collected. 

•	Slurry the salt with 1000 ml of DI water into a heat-able vessel and add 9000 ml additional DI water. 

•	Add 100 ml HCl and 250 ml formic acid

•	Heat solution to 65 C

•	Slowly add 850 ml of 6.25N NaOH maintaining the temperature at 65-70 C

•	Reduction is complete when the Pd drops to the bottom the solution becomes colorless and the pH will be between 7 – 8. some recoverable Pd remains in the liquids so save the liquids as before for cementation. 

•	Transfer the metal into a funnel and wash 3 or 4 times with warm DI water followed by washes with warm 2% w/v ammonium sulfate solution. 

•	This process produces a fine powder of high purity in excess of .999. This process was used to clean up palladium concentrates to make powder for the electronics industry as paste for the hybrid microelectronics manufacturers. High purity is related to feedstock. Highly contaminated feedstock will carry over impurities from insufficient rinsing.


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## HAuCl4 (Aug 28, 2010)

Thanks 4 metals!.

What's the expected purity of the Pt after bromate hydrolysis?.

How do you verify the purity of these metals Pt, Pd, before you deliver the refined product?.


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## 4metals (Aug 28, 2010)

Purity from both the bromate hydrolysis and the palladium refining process I posted can reach .9999 depending on your feedstock, and technique. 

The only way to determine purity at that level is by ICP. But if you have enough metal on a consistent basis to apply these methods, you can afford to do an instrumental analysis.


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## HAuCl4 (Aug 28, 2010)

Thanks a lot 4metals. I have learned very much, from you especially, and others as well. This concludes my "search for better techniques and knowledge for the 4 main metals (pun)". 

I hope one day I will land the material to refine in this fascinating field of PGMs and high purity Ag, Au, which field I had only scratched its surface previously.


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## HAuCl4 (Apr 20, 2011)

4metals said:


> 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:


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## Lou (Apr 20, 2011)

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 nitr*i*te salt) are one manner in which it's done, but again, solvent extraction works a charm. The big rider with rhodium is usually iridium, thankfully, one can oxidize Ir to (IV) in acidic milieu and selectively pull out the Rh and strip with dilute HCl. Or you can electrowin it. 

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...


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## 4metals (Apr 20, 2011)

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:


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## HAuCl4 (Apr 20, 2011)

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:


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## Lou (Apr 20, 2011)

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


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## HAuCl4 (Apr 20, 2011)

Lou said:


> 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.


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## HAuCl4 (Apr 22, 2011)

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:


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## HAuCl4 (Apr 22, 2011)

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


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## HAuCl4 (May 2, 2011)

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:


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## Lou (May 2, 2011)

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


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## freechemist (May 2, 2011)

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


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## HAuCl4 (May 3, 2011)

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?. :?:


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## Lou (May 3, 2011)

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.


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## HAuCl4 (May 3, 2011)

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


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## Lou (May 3, 2011)

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


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## freechemist (May 4, 2011)

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


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## HAuCl4 (May 8, 2011)

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.


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## 4metals (Jul 16, 2015)

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.


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