# Electrolytic Dissolution Equipment for Pd, Pt, Rh



## MaximumMax (Mar 19, 2022)

Hello, ya'll!

My R&D group is starting up a project that requires dissolution of some decent masses of Pd, Pt, and/or Rh (100g-1kg at a time). Most of our focus is on Pt right now, and we have access to virtually any reagent. Our best current procedures use heating, aqua reqia and related Cl+ reagents, but that sucks, often takes like 1week and we'd like to scale up our digestion/evaporation equipment. FWIW, my company has full chemical R&D competency; I'm an organic chemist with a pretty significant background in inorganic catalyst preparation so material handling and technical expertise are covered... on my better days.

We've been interested in microwave digestion, electrolysis, and/or reliable commercially available chemical systems. Can anyone suggest electrolytic dissolution equipment, or microwave digesters for this type of scale?

So many thanks.


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## nickvc (Mar 20, 2022)

Welcome to the forum.
Palladium is the easiest of the three to dissolve in hot nitric but platinum and rhodium is a whole lot more troublesome as they are two of the least reactive metals as you have found, I believe that the big PGM refiners use HCl and chlorine to dissolve them as AR is just too slow even at high heat .
I fear that electrolysis and commercially available kit is a non starter not to sure about microwave digestion it may be possible but I’m no expert with PGM refining but perhaps Lou or one of the other members who have more experience or specialize in it can be of more help.
You mention material handling so I hope you are aware of the dangers when refining PGMs  they are not to be ignored.


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## MaximumMax (Mar 30, 2022)

Hey man, thanks so much for your advice. I appreciate it. 

I am a professional synthetic organic chemist (I run a R&D group, owns a commercial laboratory etc.) who does a lot of pyrophoric inorganic catalyst synthesis, so I am hopefully uniquely prepared for these challenges. But my respect for these compounds is what makes me reach out. Thank you again, any knowledge that helps me not blow up will be extremely welcome.


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## orvi (Mar 30, 2022)

MaximumMax said:


> Hey man, thanks so much for your advice. I appreciate it.
> 
> I am a professional synthetic organic chemist (I run a R&D group, owns a commercial laboratory etc.) who does a lot of pyrophoric inorganic catalyst synthesis, so I am hopefully uniquely prepared for these challenges. But my respect for these compounds is what makes me reach out. Thank you again, any knowledge that helps me not blow up will be extremely welcome.


Yeah, so I am not only one professional organic chemist here 

With HCL/Cl2 method, i would use addition of some bromide source, or even bromine itself. But bromides are more convenient to get and work with.
Plain 48% HBr would be fine. Bromides have positive effect on dissolution, tend to speed things into the juice. Best would be to use HBr instead of HCL, but I don´t know if it is a viable option to you - prepare the bromide salts instead of chloride salts (catalysts are sensitive to no matter what). If you are having trouble with lenghty dissolutions, I think you are using bars or solid pieces of metal (catalysts preparation, I assume you are using standard 99,9+% pure ordinary investment bars).
Try to flatten them with roller, or just medieval way with heavy hammer and anvil. If you add even 2-3x more surface area, it will cut dissolution time in half at least. Platinum is very soft in pure form, so even the "hammer approach" wouldn´t hurt that much. For me it is always a lot of fun 

If you have means to melt and pour shot, that will also be the way to go.

Best would be to use sponge or powder. It is hard to get from commercial sources, but here, we have few professional PGM guys. I will try to PM contact Lou and discuss the issue with him - maybe he can supply you the PGMs in sponge form, or even offer you PGM salts.
In the refining facility, refining must go through the stage where the PGMs are in some soluble form or as metal sponge. This could help you to skip the annoying part and focus on your field of chemistry - maybe, it would be also cost efficient, cutting your work time down.


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## MaximumMax (Mar 30, 2022)

Hahah, thanks for reaching out, appreciate this insight a lot esp coming from another organic chemist. I'm mostly interested in catalyst prep and catalytic methods  Currently preparing and recycling hydrogenation catalysts but interested in cross-coupling work and other Pd/Pt chemistry.

I have significant current work with HI and I2, but also have a decent amount of Br2 and HBr on hand. I reckon my only concern is some avenue to isolation and precipitation after digestion? HI was good for dissolving the mirror off my porcelain tho.

I have reached out to Lou who I'm somewhat in awe of from afar. His understanding is impressive.


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## MaximumMax (Mar 30, 2022)

.


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## MaximumMax (Mar 30, 2022)

orvi said:


> Yeah, so I am not only one professional organic chemist here
> 
> With HCL/Cl2 method, i would use addition of some bromide source, or even bromine itself. But bromides are more convenient to get and work with.
> Plain 48% HBr would be fine. Bromides have positive effect on dissolution, tend to speed things into the juice. Best would be to use HBr instead of HCL, but I don´t know if it is a viable option to you - prepare the bromide salts instead of chloride salts (catalysts are sensitive to no matter what). If you are having trouble with lenghty dissolutions, I think you are using bars or solid pieces of metal (catalysts preparation, I assume you are using standard 99,9+% pure ordinary investment bars).
> ...


But yeah definitely, I try to source elemental platinum as the sponge and have increasingly made it as my own precursor. It is really really superior in all these applications. Most often I end up with casting grains commercially tho, but if its as entertaining to pound it down as you say...


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## zachy (Mar 30, 2022)

You can use an electrolytic method, if you are looking to do research and development.

You can use the principle of anodic corrosion, as follows:
You must make very thin sheets of Pt purity 999.5 and put these sheets on the anode in which a titanium cell is placed, with small titanium hooks that always hold the platinum to the titanium cell.
Weight loss increased linearly with time in the initial period of corrosion at a fixed current density. The corrosion rate increased with increasing concentration of
H2SO4.
at 40°C. The corrosion rate of the Pt anode also increased with increasing current density and temperature. At 40°C the corrosion rate was proportional to the first order of the current density.
An oxide layer will be generated on the platinum, but this layer. a current rectifier that generates pulsations must be used.


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## MaximumMax (Mar 31, 2022)

Appreciate the detail 

It would be like me to go down a rabbit hole of doing significant R&D on the electrolysis; on paper it would be so convenient if it competed with other dissolution methods (obvi). As interesting as it would be to explore, ultimately I just want an improved dissolution for a campaign of catalyst prep.

But Zachy, it seems from your post that others have found this method is more difficult and slow than it could/should be? I would certainly dive deep into this method if I thought it had some promise, I assume other researchers have tried to develop the method out and the absence of agreement in this community indicates to me it probably didn't work as well as everyone hoped?


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## orvi (Mar 31, 2022)

MaximumMax said:


> Hahah, thanks for reaching out, appreciate this insight a lot esp coming from another organic chemist. I'm mostly interested in catalyst prep and catalytic methods  Currently preparing and recycling hydrogenation catalysts but interested in cross-coupling work and other Pd/Pt chemistry.
> 
> I have significant current work with HI and I2, but also have a decent amount of Br2 and HBr on hand. I reckon my only concern is some avenue to isolation and precipitation after digestion? HI was good for dissolving the mirror off my porcelain tho.
> 
> I have reached out to Lou who I'm somewhat in awe of from afar. His understanding is impressive.


I am neck deep in research material chemistry so... Yeah, aromatic heterocycles, coupling after coupling, espetially Buchwald-Hartwig or C-H activation reactions, mainly Pd-catalyzed  real money in those ligands. I always try to go as simple as possible, but not every reaction could be done with triphenylphosphine 

Yes, exactly. Concerning catalysts, there could be huge difference in usig say hexachloroplatinate or hexabromoplatinate as starting material. But may be interchangeable.

Lou is person in right place for PGMs, lots and lots of experience.


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## orvi (Mar 31, 2022)

MaximumMax said:


> But yeah definitely, I try to source elemental platinum as the sponge and have increasingly made it as my own precursor. It is really really superior in all these applications. Most often I end up with casting grains commercially tho, but if its as entertaining to pound it down as you say...


Minor concern would be that trace ammounts of iron and iron oxides could get squished into the soft Pt, when flattened on anvil. But considering the weight of starting material, you should be OK. If you do not have experience with mechanical properties of pure Pt, you will be amazed how soft it is  not exactly butter, but very easy to shape with a little bit of force.

Platinum is tough to melt in quantity, if you do not have good equipment. Induction furnance is advised, but oxy-acetylene will work also fine. Shot will go into the solution much faster. Attention should be payed to the equipment - mostly when using oxy-acetylene. Not to cross-contaminate with metals from the nozzle when melting. In that tmeperature range, not negligible bit of copper or brass could end up in your fine metal. Not a huge ammount, but we know catalysts


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## MaximumMax (Mar 31, 2022)

Ligand prep was always a lot of fun, although admittedly I don't miss the smell of organophosphorus  In my academic background, I also focused on Pd, I worked on the Tsuji-Trost asymmetric allylation which saw me making a number of PHOX catalysts. The Hartwig-Buchwald ligands are just conceptually very cool and I'm jealous you work on them. My Schlenk line is all for straight inorganic synthesis, nowadays, and the price of palladium has risen so high


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