# Difficulty separating rhodium impurities from platinum



## Dbs (Jun 22, 2019)

Hi all, 

I'm currently playing around with 100g of dore from a mine containing roughly
2% Au 
1% Ag 
42% Pt
36% Pd
5% Rh
3% Ir
6% 

The other impurities are primarily lead copper and nickle.

I have a high mixing function on my induction furnace that gets me a complete homogenous mixture of the metals and granulated under a high pressure water het to give me nice fine granules of metal that dissolve readily in Ar @ 50 degrees C leaving behind almost pure Ru after AgCl is removed with a few PGM contaminates.

Gold is then removed and solution is percipated with zinc granules on high stirring. I know can drop metals out from AR solution but i can get a much cleaner seperation if i have the metals in powder form.

I'm left with a dense heavy precip after zinc drop. This is treated with Nitric acid for Pd and base metals leaving me with 99%+ Pt Rh and Ir.

I used 20% peroxide with 20% hcl to recover Pt and get a clean seperation of Pt from Ir and Rh however I seem to have most of the Rh going with the Pt. 

My issue is now that I have taken the Rh into solution with Pt, i cant seem to get a clean separation from the two. I've droped pt with ammonium chloride and filtered excessivly but was left with 1.5% Rh in the pt. Ive refined it further and tried dropping with potassium chloride but rh is still there. I refined again with dilute 50% Ar this time and precipitated but the Rh is still with the Pt. 

From everything I've read and everything I've experienced Rh is not supposed to be this easy to go into solution and this stubborn seperating. 

If anyone can provide some insight into whats going on here that would be greatly appreciated.


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## snoman701 (Jun 22, 2019)

How are you assaying final product?


Sent from my iPhone using Tapatalk


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## Lino1406 (Jun 22, 2019)

" was left with 1.5% Rh in the pt". 
Take a liquid sample, add sodium acetate to saturation (buffer). Add carefully sodium nitrite, NaNO2 or 60% solution, until end of brown fumes evolvement. Yellow color should develop. Heat over a plate or in a hot air flow for an hour. Add carefully ammonium hydroxide solution. A yellow/brown precipitate should form. Formula: (NH4)3Rh(NO2)6, ammonium hexanitro rhodate.


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## Dbs (Jun 22, 2019)

snoman701 said:


> How are you assaying final product?
> 
> 
> Sent from my iPhone using Tapatalk



Assays are via ICP and xrf. It seems the place I'm taking it to is picking up accurate rhodium results from powder sample that are matching icp. They are using the XL2 GOLDD xrf. I was very surprised the results matched up.


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## Dbs (Jun 22, 2019)

Lino1406 said:


> " was left with 1.5% Rh in the pt".
> Take a liquid sample, add sodium acetate to saturation (buffer). Add carefully sodium nitrite, NaNO2 or 60% solution, until end of brown fumes evolvement. Yellow color should develop. Heat over a plate or in a hot air flow for an hour. Add carefully ammonium hydroxide solution. A yellow/brown precipitate should form. Formula: (NH4)3Rh(NO2)6, ammonium hexanitro rhodate.



Thanks lino, I'll give this a try. I was going to try precip the rhodium out however I'm just confused as to why it's following the platinum despite the relatively low ORP dissolving methods I'm using.


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## cuchugold (Jun 25, 2019)

If you have a near pure Pt-Rh powder. Dissolving the Rh with hot H2SO4 will do. Also fusion with NaHSO4 will remove most of the Rh. What is your target metal?.

If your target metal (most of the $$$) is Pt, and you wish to get it pure, you probably cannot avoid to do Hydrolysis or Solvent extraction or both.

Everything is somewhere in the forum, but if you want help, you must be very specific in stating your "situation".

Welcome to Hell.


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## anachronism (Jun 25, 2019)

Firstly welcome to you. 8) 8) 

Secondly why are you even bothering trying to separate? Sell it as it is. Is there a financial gain to you for all the work separating? You're in Australia. These guys are used to mixed product so you won't get your butt handed to you. 

Jon


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## Dbs (Jun 25, 2019)

cuchugold said:


> If you have a near pure Pt-Rh powder. Dissolving the Rh with hot H2SO4 will do. Also fusion with NaHSO4 will remove most of the Rh. What is your target metal?.
> 
> If your target metal (most of the $$$) is Pt, and you wish to get it pure, you probably cannot avoid to do Hydrolysis or Solvent extraction or both.
> 
> ...



Thanks for the feedback. The goal is to remove the rhodium that's following the platinum. I'm thinking to try 98% sulfuric @ 125c with 1% NaCl as I am not set up to well for the fume managment for fusions and something I have less experience with. Either that or try and precip the rhodium out.


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## cuchugold (Jun 26, 2019)

It takes some time and it is somewhat dangerous, but hot H2SO4 will clean your Pt powder from Rh. 
Any Ir will stay there with the Pt. 
After that, you have to decide how pure you want your Pt. 
You probably know already that all these separations are not perfect and that is wise to keep it as simple as possible to avoid waste.
It is a great learning experience, and quite addictive. Probably not very profitable except for a few people.


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## Lou (Jun 26, 2019)

Want to sell it as is?


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## Dbs (Jun 27, 2019)

cuchugold said:


> It takes some time and it is somewhat dangerous, but hot H2SO4 will clean your Pt powder from Rh.
> Any Ir will stay there with the Pt.
> After that, you have to decide how pure you want your Pt.
> You probably know already that all these separations are not perfect and that is wise to keep it as simple as possible to avoid waste.
> It is a great learning experience, and quite addictive. Probably not very profitable except for a few people.



I'm pretty well set up in terms of safety and have worked with sulfuric way in excess of what's needed for the rhodium. I've had a few discussions with some people and going to try a few things to selctivly precip the rhodium. Surprisingly the Ir has been easy to completely remove, as has the Ru without forming any tetroxides. It's just the rhodium that's been hanging around. But yes it is good fun working through and being able to have enough quantity to work through these issues. Gold and silver has become tedious as I've processed much of it in my time. I have some really interesting pics that I'll post as I'm trying a whole bunch of out the box ideas to leave behind certain metals and some strange things are happening. One in particular is pd droping as a black crystal when heating solution after ammonium chloride drop for Pt. I've spent alot of time reading the forums and hoping to share some of my experiences from the past few years working with Pgms to simplify the procedures on here.


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## Dbs (Jun 27, 2019)

Lou said:


> Want to sell it as is?



I've got a stable supply of all pgms coming through aside from osmium so happy to discuss further if you PM me.


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## cuchugold (Jun 28, 2019)

If you have no Ir in the mix, and only Pt and Rh, one procedure that works well is to dissolve the mixed powders with HCL + sodium chlorate, and do a solvent extraction with TBP. The Rh stays in the aqueous portion and the Pt goes into the TBP. Try a search in the forum or specifically in the library.

Another route is the hydrolysis. More artistic and scenic, but also mentally rewarding. It's also in the forum somewhere. Amazing how mentally addictive this field is for most people that get involved.


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## Lou (Jun 28, 2019)

Problem with TBP is the low loading capacity, issues with Fe(III), so called emulsion formation (I’ve never experienced the mayonnaise), and it loves gold. As a matter of fact, TBP is pretty darn good for gold. 

All this usually means TBP better for Ir(IV) than Pt(IV) in most instances. Both need continuous countercurrent extraction because even scrubbing the loaded organic loses some Pt as main driver is [H+]. There are some tricks to TBP and Pt particularly stripping and precipitating the platinum.


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## cuchugold (Jun 28, 2019)

Lou said:


> Problem with TBP is the low loading capacity, issues with Fe(III), so called emulsion formation (I’ve never experienced the mayonnaise), and it loves gold. As a matter of fact, TBP is pretty darn good for gold.
> 
> All this usually means TBP better for Ir(IV) than Pt(IV) in most instances. Both need continuous countercurrent extraction because even scrubbing the loaded organic loses some Pt as main driver is [H+]. There are some tricks to TBP and Pt particularly stripping and precipitating the platinum.


I guess I'll take this intellectual passion to my grave! :lol:


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## Lou (Jun 28, 2019)

Don't take it critically, take it from the perspective of that's what I experienced. Hydrolysis sucks too.

Who wants to boil a bunch of platinum in solution with excess muriatic acid to convert it back into chloroplatinic acid? Not me...besides, that's what cation exchange resin is for


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## cuchugold (Jun 28, 2019)

Not at all Lou. I'm just here in earth... in a learning trip. Why not pursue one's passion?. Sometimes it feels sinful, but... Life is short. :G 

For others: Lou said that TBP will absorb anything with oxidation +4... Fe++++, Pt++++, Au++++, etc (even Pu++++), but not +3 like Rh+++. He also said that stripping is not straight forward. And he also said that state-of-art professional (for money) processing for Pt-Rh separation uses resin processes.

Pt is 20 times scarcer than Au , yet sells at a discount. Maybe someone can profit from that!. :G


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## zachy (Feb 3, 2021)

Can platinum be precipitated with potassium chloride? to avoid the cooprecipitation of Iridium and Rhodium.


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## Lino1406 (Feb 3, 2021)

KCl (and NH4Cl) precipitates platinum at first, iridium after a while. But some also stay in solution


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## Lou (Feb 4, 2021)

zachy, you'll get better separation from Rh than you will from Ir. 

Both will come down together.


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## zachy (Feb 15, 2021)

It is very annoying to find Iridium in the final platinum product, it causes many problems, I want to obtain 999.5 Pt, but iridium is very persistent in small traces, 200 ppm to 500 ppm.


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