K3(RhCl6) solubility compared to (NH4)3(RhCl6)

[orvi]

Maybe the question for more knowledged refiners here.

How soluble is potassium hexachlororhodate salt compared to ammonium one ? From safety reasons, I would more likely use KCl to precipitate batch of PtPd salts from PtPdRh mixture. But hence i don´t know the solubility of potassium Rh salt, i cannot conclude if the intended procedure would be of any help in means of separation of Rh. I know the efficiency will be bad, and much of the Rh will be lost in mixed PtPd salts. But my time to finish this particular batch is coming to the end, so this is only thing I could come up with to scavenge some Rh enriched fraction. Otherwise I will lose it all.
From literature i could only find the solubility of (NH4)3(RhCl6) to be 40g/L in water and 12g/L in 1M NH4Cl solution.

Any data or comparison of K salt to NH4 salt of Rh would be greatly appreciated.
Thank you for you reply
Orvi

 

[Lou]

They're about equivalently soluble. I wouldn't make the K salt of Rh if it can be avoided as it is difficult to convert it back to H3RhCl6 because it begins speciating/hydrolyzing outside of strong HCl liquors. Any way you slice it--with what you're doing-- there will be significant Rh in all of your products. If you're going from the K-hexachlormetallates, it'll probably concentrate the most with the Pd, as K2PdCl6 requires pretty extremely acidic, oxidizing conditions (in this case, the high acidity >6M HCl) to get a complete (<30 ppm Pd) precipitation. This excess acidity ensures more Rh is as [RhCl6]3- and will come down.

It seems you are engaged more in the recovery rather than final refining. But in final refining, usually the best solution for Pd is SX (after Au gone), the Pt direct precipitation as a chlorometallate salt with follow up hydrolysis after redissolving and/or converting the X2PtCl6 to H2PtCl6. During the hydrolysis occluded base metals and co-precipitated Ir/Rh can be hydrolyzed out, and the Ir/Rh oxidizes can then be redissolved (mind the Rh(IV) and initially cationic behavior!), converted into nitrites and freed of other PGM, or separated as the chlorocomplexes in strongly oxidizing HCl by TBP for Ir(IV) with a DETA precipitation for the Rh.

Jeez, what a drag separating all these can be. Fun part is that there's so many ways!

 

[orvi]

They're about equivalently soluble. I wouldn't make the K salt of Rh if it can be avoided as it is difficult to convert it back to H3RhCl6 because it begins speciating/hydrolyzing outside of strong HCl liquors. Any way you slice it--with what you're doing-- there will be significant Rh in all of your products. If you're going from the K-hexachlormetallates, it'll probably concentrate the most with the Pd, as K2PdCl6 requires pretty extremely acidic, oxidizing conditions (in this case, the high acidity >6M HCl) to get a complete (<30 ppm Pd) precipitation. This excess acidity ensures more Rh is as [RhCl6]3- and will come down.

It seems you are engaged more in the recovery rather than final refining. But in final refining, usually the best solution for Pd is SX (after Au gone), the Pt direct precipitation as a chlorometallate salt with follow up hydrolysis after redissolving and/or converting the X2PtCl6 to H2PtCl6. During the hydrolysis occluded base metals and co-precipitated Ir/Rh can be hydrolyzed out, and the Ir/Rh oxidizes can then be redissolved (mind the Rh(IV) and initially cationic behavior!), converted into nitrites and freed of other PGM, or separated as the chlorocomplexes in strongly oxidizing HCl by TBP for Ir(IV) with a DETA precipitation for the Rh.

Jeez, what a drag separating all these can be. Fun part is that there's so many ways!

Thank you for your insight. I will take your advice and proceed with ammonium salts.e

Yes, I am more oriented to recovery of Rh. After nearly half-year venture, I don´t currently have any usable experience with recovery or refining PGMs. Lots of time invested, lots of unsuccessful experiments. From the base cat material, we are doing great job getting the values to the solution by numerous steps of incineration, melting, dissolving etc... Ordinarily Rh comes along PtPd in concentrations lower than 1% in our product. And was passed without payment anytime. This time, material is like 2% Rh - and i want to squeeze something out for later "playing around" - to learn more about PGM refining, because it seems that revealing the ways how to do it usefully will take years with current progress.

But I am not giving up

 

[goldandsilver123]

They're about equivalently soluble. I wouldn't make the K salt of Rh if it can be avoided as it is difficult to convert it back to H3RhCl6 because it begins speciating/hydrolyzing outside of strong HCl liquors. Any way you slice it--with what you're doing-- there will be significant Rh in all of your products. If you're going from the K-hexachlormetallates, it'll probably concentrate the most with the Pd, as K2PdCl6 requires pretty extremely acidic, oxidizing conditions (in this case, the high acidity >6M HCl) to get a complete (<30 ppm Pd) precipitation. This excess acidity ensures more Rh is as [RhCl6]3- and will come down.

It seems you are engaged more in the recovery rather than final refining. But in final refining, usually the best solution for Pd is SX (after Au gone), the Pt direct precipitation as a chlorometallate salt with follow up hydrolysis after redissolving and/or converting the X2PtCl6 to H2PtCl6. During the hydrolysis occluded base metals and co-precipitated Ir/Rh can be hydrolyzed out, and the Ir/Rh oxidizes can then be redissolved (mind the Rh(IV) and initially cationic behavior!), converted into nitrites and freed of other PGM, or separated as the chlorocomplexes in strongly oxidizing HCl by TBP for Ir(IV) with a DETA precipitation for the Rh.

Jeez, what a drag separating all these can be. Fun part is that there's so many ways!

Recently I got TBP from the nuclear waste management, that is conveniently located at 100 m from us, and it works great to remove Ir contamination. My first experience with solvent extraction of metals. It does extract copper together with Ir.

The solvent for Pd is dioctyl sulfide?

The Rh (IV) is all converted back to Rh (III) just with heating in acidic medium or for the last part a reductant is needed?

 

[Lou]

TBP/IsoParM (what I use) only good for large quantities if you're using a centrifuge. Then you still have to strip it. I wouldn't call it great either as it basically anion exchanges a bunch of BS but apparently not [RhCl6]3-.

Yes, DOS or DHS both work well. Give them two hours of good stirring, then a 1 M HCl rinse. Make sure no gold is in solution.

 

[goldandsilver123]

I used pure TBP, it was somewhat difficult for the phases to separate completely.


I even saw the mayonnaise when washing with water but eventually it separated.




I will try to find IsoPar M here


No gold means no g/L or no ppm?

 

[Lou]

You can use kerosene if you can't get the paraffin oil.

No gold means...NO GOLD. As in it must be precipitated out, both for dialkylsulfides and TBP, because the gold will go into the solvent.