# Metalic catalytic converters



## sayf (Dec 8, 2022)

Hello guys, i got few kilograms of the metallic catalytic converter (MCC) which i think they are stainless steel similar to the one in the photo, i analyzed them using an XRF machine and the reslut was 5 grams of Pd and 0.35 grams of Rh per kilogram of MCC 
As am planning to leach the palladium using hot concentrated nitric acid i think the rhodium will be untouched 
So guys do you have any tips to recover rhodium or a better method to recover the both metals 
Thank you
regards


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## Yggdrasil (Dec 8, 2022)

sayf said:


> Hello guys, i got few kilograms of the metallic catalytic converter (MCC) which i think they are stainless steel similar to the one in the photo, i analyzed them using an XRF machine and the reslut was 5 grams of Pd and 0.35 grams of Rh per kilogram of MCC
> As am planning to leach the palladium using hot concentrated nitric acid i think the rhodium will be untouched
> So guys do you have any tips to recover rhodium or a better method to recover the both metals
> Thank you
> regards


I have done one of these, some years ago.
I dissolved the structure in HCl and then leached the remaining wash coat.
It took a long time and about 5L of acids if I remember correctly.
I ended up with around 100 grams of wash coat. Much easier to treat 100 grams of powder than a full cat.
But it took time and created a lot of waste.

For Rhodium, if you keep the full metal cat it will be hard I think.
Rhodium can be fused with Sodium Peroxide, Sodium Sulfate or other suitable salts or dissolved in fairly concentrated Sulfuric acid and Salt.


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## sayf (Dec 8, 2022)

Yggdrasil said:


> I have done one of these, some years ago.
> I dissolved the structure in HCl and then leached the remaining wash coat.
> It took a long time and about 5L of acids if I remember correctly.
> I ended up with around 100 grams of wash coat. Much easier to treat 100 grams of powder than a full cat.
> ...


If i correctly understand you, you dissolved the stainless steel structure with HCL and dealt with the remaining undissolved powder which should contain the PGMs , but doesnt the palladium partially or totally dissolve in HCL too with long time? and if oxiginated with time it will also dissolve part of the rhodium since rhodium is soluble in chlorine gas ?


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## Yggdrasil (Dec 8, 2022)

sayf said:


> If i correctly understand you, you dissolved the stainless steel structure with HCL and dealt with the remaining undissolved powder which should contain the PGMs , but doesnt the palladium partially or totally dissolve in HCL too with long time? and if oxiginated with time it will also dissolve part of the rhodium since rhodium is soluble in chlorine gas ?


Some will dissolve, but that is solved by the stock pot.
I do not think Rhodium is soluble in Chlorine gas in appreciable amount at least.
No need to bubble air through the HCl during this.
If you have plenty of Nitric you can go your way, I did not when I did this.
Rhodium "needs" to be fused as described or with hot strong Sulfuric and Salt.
That will be hard when the cat is whole.


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## orvi (Dec 8, 2022)

Yggdrasil said:


> Some will dissolve, but that is solved by the stock pot.
> I do not think Rhodium is soluble in Chlorine gas in appreciable amount at least.
> No need to bubble air through the HCl during this.
> If you have plenty of Nitric you can go your way, I did not when I did this.
> ...


With PGMs, you will slice it whatever you will do. Pd is somewhat soluble in hydrochloric acid upon prolonged heating, in vessel open to air. Rhodium will also dissolve to some degree, but much much less than Pd. It would be wise to reduce all possible PdO present to palladium metal by heating the cat in reducing atmosphere (putting it into the graphite crucible and let it be reduced by CO created from carbon and air). Otherwise, some Pd will be always left as resistant PdO. By smelting route, you obviate this issue.


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## stoneware (Dec 8, 2022)

Using a small hydraulic press placed the foil onto a sheet then deformed the foil in several directions the wash coat then falls out, another method used was to place the canister in an electrolyte as the anode then plate out some of the metal undermining the wash coat.

My home made ultrasonic tank fitted with four 100 watt 28 Mhz transducers worked on foils but they eventually have to be turned end for end as the cavitation bubbles produced at this frequency are fairly large and will not penetrate full length foils.

Used the tank on comb after leaching, thought the ultrasonic would destroy the comb, turns out the comb is a soft material that absorbs the shock.from acoustics.

Once added a couple of drops of dish soap to the water in the ultra sonic tank big mistake, made an unbelievable amount of foam.


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## MicheleM (Dec 8, 2022)

stoneware said:


> Using a small hydraulic press placed the foil onto a sheet then deformed the foil in several directions the wash coat then falls out, another method used was to place the canister in an electrolyte as the anode then plate out some of the metal undermining the wash coat.
> 
> My home made ultrasonic tank fitted with four 100 watt 28 Mhz transducers worked on foils but they eventually have to be turned end for end as the cavitation bubbles produced at this frequency are fairly large and will not penetrate full length foils.
> 
> ...


I do not understand why you write this: it is failed attempt?
, can you explain a little more in detail?


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## Yggdrasil (Dec 8, 2022)

orvi said:


> With PGMs, you will slice it whatever you will do. Pd is somewhat soluble in hydrochloric acid upon prolonged heating, in vessel open to air. Rhodium will also dissolve to some degree, but much much less than Pd. It would be wise to reduce all possible PdO present to palladium metal by heating the cat in reducing atmosphere (putting it into the graphite crucible and let it be reduced by CO created from carbon and air). Otherwise, some Pd will be always left as resistant PdO. By smelting route, you obviate this issue.


Will smelting be feasible for metal matrix cats?
Quite a lot of metal to smelt.


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## Yggdrasil (Dec 8, 2022)

MicheleM said:


> I do not understand why you write this: it is failed attempt?
> , can you explain a little more in detail?


I can’t find this text in the post you replied to?
Did you intend to reply to another post, or do I need one more set of glasses?


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## MicheleM (Dec 8, 2022)

Post Number 6 by @stoneware


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## stoneware (Dec 8, 2022)

MicheleM said:


> I do not understand why you write this: it is failed attempt?
> , can you explain a little more in detail?


As they say a picture is worth a thousand words.


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## stoneware (Dec 8, 2022)

Precious metals in the foam.


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## stoneware (Dec 8, 2022)

MicheleM said:


> Post Number 6 by @stoneware


This link, Foil Converters Electrolysis


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## stoneware (Dec 8, 2022)

MicheleM said:


> I do not understand why you write this: it is failed attempt?
> , can you explain a little more in detail?


What's not to understand, this assay speaks volumes.


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## Yggdrasil (Dec 9, 2022)

MicheleM said:


> Post Number 6 by @stoneware


Ha had only one in this thread before you posted, which thread did you intend to post in?


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## Yggdrasil (Dec 9, 2022)

stoneware said:


> What's not to understand, this assay speaks volumes.
> 
> View attachment 53594


Since there is no additional explanation, one needs to go into the original thread to puzzle this one together, I believe.
This is just an assay.


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## orvi (Dec 9, 2022)

Yggdrasil said:


> Will smelting be feasible for metal matrix cats?
> Quite a lot of metal to smelt.


It depends. If you can enrich the stuff by taking off the layer, then you proceed with it. If there is nothing to do with it and metals are tightly bond to the steel surface, yes, you smelt it. Also depends on the matrix heavily - if it is predominantly iron, you can melt it all down and electrorefine the metal. If you tune the potential (voltage), you can easily achieve very good separation of PGMs to anode slimes (potential of Fe roughly -0,44, Pd around 0,8V). But to be honest, it does not work well on many occasions.
But I must admit, we have done batches of powdered catalytic materials on Fe2O3 and various other oxides (Al, Cr, Ni etc.), where PGMs were present at less than 1wt% quantities. And this is very painful. Slaging iron oxides at this scale (one 25kg bag and more) is practically non viable option... Very very difficult to process. Eventually, we somehow managed to get it done by combination of scorification, smelting and collector metal collecting the metallic fraction, but it was such a pain. Leaching was also an option, but very nasty retention of PGMs on matrix was observed. Theoretically 3 leaching and thorough washing cycles were needed to achieve more than 90% recovery.


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## DylanCaldwell (Dec 9, 2022)

Yggdrasil said:


> Some will dissolve, but that is solved by the stock pot.
> I do not think Rhodium is soluble in Chlorine gas in appreciable amount at least.
> No need to bubble air through the HCl during this.
> If you have plenty of Nitric you can go your way, I did not when I did this.
> ...


When you mention hot concentrated sulfuric and salt, are you referring to sodium chloride? Does that not create toxic hydrogen chloride gas? If you were looking for a gram or two of rhodium to dissolve, how much sodium chloride would you add per liter of sulfuric? Thank you and I appreciate your insights.


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## DylanCaldwell (Dec 9, 2022)

Yggdrasil said:


> I have done one of these, some years ago.
> I dissolved the structure in HCl and then leached the remaining wash coat.
> It took a long time and about 5L of acids if I remember correctly.
> I ended up with around 100 grams of wash coat. Much easier to treat 100 grams of powder than a full cat.
> ...


Could you please elaborate on your example of rhodium dissolution with sodium peroxide, since it is a base, wouldn’t this neutralize your acid? Also could you explain the reaction with sodium sulfate, as it would create sulfuric acid when mixed with hydrochloric acid. Is hcl and sulfuric acid mixed with chlorine a good idea for rhodium dissolution?


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## Yggdrasil (Dec 10, 2022)

DylanCaldwell said:


> When you mention hot concentrated sulfuric and salt, are you referring to sodium chloride? Does that not create toxic hydrogen chloride gas? If you were looking for a gram or two of rhodium to dissolve, how much sodium chloride would you add per liter of sulfuric? Thank you and I appreciate your insights.


If you do not work with PGM salts regularily and have a dedicated lab and safety gear for it, I do not recommend dissolving them.
Better use a collector metal and smelt them, copper will manage this.


DylanCaldwell said:


> Could you please elaborate on your example of rhodium dissolution with sodium peroxide, since it is a base, wouldn’t this neutralize your acid? Also could you explain the reaction with sodium sulfate, as it would create sulfuric acid when mixed with hydrochloric acid. Is hcl and sulfuric acid mixed with chlorine a good idea for rhodium dissolution?


Sodium Peroxide is not used for dissolving the Rhodium.
It is fused which means you mix the peroxide and metals powder intimately and then melt the salt.metal mixture.
This converts the Rhodium to a salt form that easily can be dissolved.
Same with Sodium Sulfate


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## sayf (Dec 10, 2022)

Yggdrasil said:


> If you do not work with PGM salts regularily and have a dedicated lab and safety gear for it, I do not recommend dissolving them.
> Better use a collector metal and smelt them, copper will manage this.
> 
> Sodium Peroxide is not used for dissolving the Rhodium.
> ...


I think copper is not a good collector for rhodium its good for platinum and palladium, i read in many articles that nickel sulphate is the best for that purpose with a borax flux 
My problem is with the rhodium not the palladium it self 
I can easily leach palladium using concentrated nitric acid 
But rhodium will not be touched, so if i use aqua regia after that ill get a huge amount of iron dissolved in aqua regia with that small amount of rhodium. So am thinking that after leaching the palladium with nitric acid ill give a good water wash to the stainless steel structure and then dissolve it with HCL then ill deal with the remaining stuff


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## Yggdrasil (Dec 10, 2022)

sayf said:


> I think copper is not a good collector for rhodium its good for platinum and palladium, i read in many articles that nickel sulphate is the best for that purpose with a borax flux
> My problem is with the rhodium not the palladium it self
> I can easily leach palladium using concentrated nitric acid
> But rhodium will not be touched, so if i use aqua regia after that ill get a huge amount of iron dissolved in aqua regia with that small amount of rhodium. So am thinking that after leaching the palladium with nitric acid ill give a good water wash to the stainless steel structure and then dissolve it with HCL then ill deal with the remaining stuff


Copper is what the big guys (Refineries) use.
But according to Lou, Gold is the "best" collector for Rhodium.....
Nickel Sulfide is used for assays so Nickel may be a good collector for Rhodium, but I really do not know for sure.


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## orvi (Dec 10, 2022)

sayf said:


> I think copper is not a good collector for rhodium its good for platinum and palladium, i read in many articles that nickel sulphate is the best for that purpose with a borax flux
> My problem is with the rhodium not the palladium it self
> I can easily leach palladium using concentrated nitric acid
> But rhodium will not be touched, so if i use aqua regia after that ill get a huge amount of iron dissolved in aqua regia with that small amount of rhodium. So am thinking that after leaching the palladium with nitric acid ill give a good water wash to the stainless steel structure and then dissolve it with HCL then ill deal with the remaining stuff


If you manage to get rhodium in solution, you already partially won  But I found that no matter what you do, when you aim to dissolve just Pd from PtPdRh mixture as cemented powders with nitric acid, all three dissolve to some extent. Even rhodium after some time. Not very good separation technique.

Actually, if you manage to attack the surface of the metal with layer of deposited Rh, you can dross it off  Acid will undermine the largely insoluble Rh particles and make them fall off the matrix. Very convenient is the use of ultrasonic cleaner to accomplish this. Ultrasound dross off the particles very effectively 

There are many good collector metals for rhodium in terms of capacity and melting point depression. Alminium and bismuth being accessible and working to solubilize the Rh in the metal melt. Lead is very inefficient for this. Copper works OK, nickel is also good, but depression in melting point is not that great. Mentioned gold as collector for Rh is also nice, but mostly in terms of later workup. Aluminum is giving nice possibility of inquartation in strong NaOH solution, leaving metallic Rh as sponge (similar to gold inquartation, I have done this with PtRh alloys several times). But you need to alloy it at higher than 18-20% PGM or other insoluble metals, otherwise it forms very hard to settle and agglomerate nano-suspensions. 

Then, on the other hand, it is also important to get the Rh out - and for that, not that many metals stands out  With copper, dissolution in AR (assuming no Pb and Ag contamination) is relatively OK, if the alloy is not very high Rh content. Bismuth permanently cause issues in later treatment, as with Rh - it cannot be completely cupelled out, and aqueous bismuth chemistry is a nightmare 

Lastly, if you manage to get insoluble rhodium powder, many refiners gladly take this - no need to melt it. It gave them trouble afterwards, as they will eventually need to re-refine and purify it, and dissolution of Rh in bulk is much more tedious than dissolution of fine powder.


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## sayf (Dec 17, 2022)

orvi said:


> If you manage to get rhodium in solution, you already partially won  But I found that no matter what you do, when you aim to dissolve just Pd from PtPdRh mixture as cemented powders with nitric acid, all three dissolve to some extent. Even rhodium after some time. Not very good separation technique.
> 
> Actually, if you manage to attack the surface of the metal with layer of deposited Rh, you can dross it off  Acid will undermine the largely insoluble Rh particles and make them fall off the matrix. Very convenient is the use of ultrasonic cleaner to accomplish this. Ultrasound dross off the particles very effectively
> 
> ...


Thank you very much orvi, can you give me more details about the ultrasonic cleaner such as the needed frequency, and will it make all the PGM metals in the MCC fall ?
Will these ones in the attached photo work?


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