# How insoluble is rhodium in nitric acid ?



## orvi (Nov 28, 2021)

Hi
this is maybe dumb question, but did anyone noticed any kind of dissolution of rhodium in nitric acid (cold,boiling, 65%..., 100%...) ? Just nitric, no added HCl or H2SO4 or anything, straight nitric. Pretty much every textbook or paper says it is completely insoluble in nitric. With platinum, many pages said that it is insoluble in nitric and hence i was unhappy to see it goes into the solution (HNO3) in not the negligable quantities.
I know and i performed the dissolution of Rh material in AR and it gone to some extent, but the Rh was reluctant to go into the solution. This give me some confidence that nitric does not anything to Rh. But after being previously skunked by textbooks, i rather ask here 
I just want to be sure that i dont gonna make another mess. Rh is in very finely divided state in the material, structurally it is close to Ranney Ni, with very high surface area. Active.
With relatively low content of Rh in the material (few % at most) im bit paranoid about accidentaly dissolving part of it, which will then be painful to recover from base metals and other PGM present (Pd mainly). 
Practical observations would be greatly appreciated.
Thanks


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## Lino1406 (Nov 28, 2021)

On the contrary, nitric acid will passivate rhodium surface, so preventing its dissolution, especially if alone


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## orvi (Nov 28, 2021)

Lino1406 said:


> On the contrary, nitric acid will passivate rhodium surface, so preventing its dissolution, especially if alone


that makes sense, thank you for the point. in these terms i am worried that platinum, which is also present in the material in few %, will dissolve into nitric solution (it will hapen) and MAYBE possibly reprecipitate on the undissolved less noble metals. but if Rh is passivated, then this will not likely to happen.


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## Lou (Nov 28, 2021)

It dissolves at 260 C and 2500+ PSI in nitric.


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## 4metals (Nov 28, 2021)

That is pretty hot and the pressure is up there. If that is what is required to break the passivation Lino mentioned, I dare say a heavy stainless pressure vessel wouldn’t stand a chance. 
What equipment is used for this digestion? And is it do able in anything but lab sample quantities? Anything like a microwave bomb used in analytics?


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## orvi (Nov 29, 2021)

very interesting numbers, Lou  im just wondering, like 4metals, how this could be done except sealed glass ampoules. not attempting to even try this on my own.
my aim is to reduce bulk of the PGM, except rhodium. after some thinking, i come up with idea to alloy PGM residue with copper or aluminium, forming uniform (hopefully not granular - with intermetallic grains of PGMs) alloy, which could be easily digested in nitric acid or NaOH (for Al), forming very fine PGM precipitate - this could be very prone to dissolution in nitric acid, i expect even a good part of Pt would go into the solution after prolonged boiling (65% nitric), but this is OK. Im only curious about that finely divided rhodium... Would be great if this pathway work. That is why i posted here, because i know there are experts in the field, which know better than textbooks.
I found online this "paper" (link printscreened on the picture) on rhodium properties, which say, that after alloying Rh with Cu, it will dissolve in HNO3... That is exactly what i wanted to do.


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## Lou (Nov 29, 2021)

4metals, it is very hot and very nasty. We have a 2 gallon C276 autoclave that goes to about 5000 psi. That's what's needed to dissolve Ir/Ru sponge via what's called a Carius Tube digestion. We would use pure quartz tubes, 37% w/v HCl and fuming nitric acid. You put that into the container, evacuate it, and then add a known quantity of CO2 from the tank and heat it until you're at pressure. They're very long and skinny. 

Last year I worked with these people to get a method to dissolve Ru/Ir but we didn't have great success at the 500+ mg scale we need to do ICP-OES on 4N+ Ir and Ru sponge and get the LOD we need. Rh would dissolve however, so I can say it's Ir>~Ru>>Rh insofar as chemical resistance is concerned with oxidizing/complexing aqueous media. Download Methods - UltraWAVE - Milestone
They have a great system but they're near 6 figures and only do about 70% of the type of work I need. I usually rely on Na2O2 as the sledge hammer. 

As to inorganic ventures (good people by the way), the problem is they collate a bunch of theory. For instance, if alloyed in Pt, it is definitively NOT attacked to any great degree by nitric acid but the aqua regia treatment they mention will get it done. Then of course the Rh must be removed via hydrolysis. That Rh(OH)4 is then cationic when it is redissolved. Rh chemistry is odd.

One way to get bulk rhodium soluble is crush it and then to alloy it with Cu, Zn, Al (one of them), digest away those metals, then fuse it with NaOH/Na2O2. That product--which may be pyrophoric or at least smoke on standing-- is then soluble in HCl and gives the characteristic anionic wine red chlororhodate species. Nitre can be substituted but it decomposes into nitrite at temperature and that may cause problems for aqueous work up depending on where the refining is going and what else is in it.

Generally many analytical labs will do the Cl2+NaCl method which I've already shown on this forum, years ago.


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## Yggdrasil (Nov 29, 2021)

Thanks for yet another informative post Lou.
I guess the Carius tube digestion are impractical for other than analytic work?
Is Oxone (Potassium peroxymonosulfate) usable as fusing agent in these scenarios?

What function has the NaOH with the Na2O2? Forming Rhodium Hydroxide?

Regards Per-Ove


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## Lou (Nov 30, 2021)

Oxone gives up its oxygen readily and would probably end up being just like melting it with bisulfate, where the active oxidizing agent is mostly SO3. As for Carius...guess it depends on the size of the autoclave?? Usually the big issue with Ir is getting it fine enough to dissolve under those conditions without contaminating it with the media used to comminute it. This is why many people press pellets and do spark-OES or melt with UHP indium as a binder and do GD-MS.

I think it's sodium rhodite/rhodate that forms. Palladates, rhodates, iridates...they all do that. They all seem soluble in aqua regia or very concentrated hydrochloric acid.


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## goldandsilver123 (Nov 30, 2021)

That autoclave method is so interesting, I've searched for it, but didn't find much about it.

If the quartz ampoule sealed? or the CO2 is poured inside the autoclave with the quartz tubes open?

Does Rh(OH)4 turns to Rh3+ on boiling the HCl solution? First time seeing Rh4+

The method that Freechemist posted with bisulfate and NaCl does work, but it's too much expensive and time consuming...
How long it would take for total dissolution of rhodium?


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## Lou (Nov 30, 2021)

The tubes can be open or sealed. If open, enough gas (in this case, nitrogen) is introduced to keep sufficient over pressure to prevent boiling of the acids. If sealed, CO2 is added to reactor.

Rh in the tube is done in 30-60 minutes.

Check out the ultraclave. For Rh for plating solution quantities (say 20 g per hour) it may be all you need.


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## orvi (Dec 1, 2021)

Lou said:


> 4metals, it is very hot and very nasty. We have a 2 gallon C276 autoclave that goes to about 5000 psi. That's what's needed to dissolve Ir/Ru sponge via what's called a Carius Tube digestion. We would use pure quartz tubes, 37% w/v HCl and fuming nitric acid. You put that into the container, evacuate it, and then add a known quantity of CO2 from the tank and heat it until you're at pressure. They're very long and skinny.
> 
> Last year I worked with these people to get a method to dissolve Ru/Ir but we didn't have great success at the 500+ mg scale we need to do ICP-OES on 4N+ Ir and Ru sponge and get the LOD we need. Rh would dissolve however, so I can say it's Ir>~Ru>>Rh insofar as chemical resistance is concerned with oxidizing/complexing aqueous media. Download Methods - UltraWAVE - Milestone
> They have a great system but they're near 6 figures and only do about 70% of the type of work I need. I usually rely on Na2O2 as the sledge hammer.
> ...


Thanks for very interesting information. I appreciate the expertise always given in your posts. When I started at the university as organic chemist, i thought that inorganic chemistry is something what starts to be boring like year after doing so, but i was horribly wrong  in next few years i worked with transition metal catalysts (with funding that we "have", all made on my own from basic, mostly PGM salts) and practically i was more like inorganic chemist 
As you start to add more and more elements to the mixtures, much more is going on, and it started to fascinate me everyday i stumble across some unexpected results from XRF or how you cannot separate 6 elements in 21. century in some easy and elegant fashion  
Started to doing some refining, as a side "job", picked up the most difficult category of metals, definitely sure that with level of my knowledge it would be easy and straightforward... haha  wrong

But in the next few days, we are planning to conduct few experiments, in "analytical manner-XRF backed", so if some at least somewhat interesting firures could be made out of it, ill post it here


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## Yggdrasil (Dec 1, 2021)

Lou said:


> Oxone gives up its oxygen readily and would probably end up being just like melting it with bisulfate, where the active oxidizing agent is mostly SO3. As for Carius...guess it depends on the size of the autoclave?? Usually the big issue with Ir is getting it fine enough to dissolve under those conditions without contaminating it with the media used to comminute it. This is why many people press pellets and do spark-OES or melt with UHP indium as a binder and do GD-MS.
> 
> I think it's sodium rhodite/rhodate that forms. Palladates, rhodates, iridates...they all do that. They all seem soluble in aqua regia or very concentrated hydrochloric acid.


Thanks again Lou.

In your initial post you implied that it was not viable to use bisulfate, is that due to price/time or speed and efficiency?
Bisulfate is cheap and readily available, Sodium Peroxide is hard to get and expensive.

Are the sealed Carius tubes flexible enough to not crack if the differential pressure get too high?
And why CO2?
Will N2 or Ar be too expensive or do CO2 participate in the reaction?

What about Oxone in the Carius tubes?

Many why's here but I got curious


Thanks again for your excellent posts Lou.

Regards Per-Ove

Edited for clarity.


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## goldandsilver123 (Dec 1, 2021)

Lou said:


> The tubes can be open or sealed. If open, enough gas (in this case, nitrogen) is introduced to keep sufficient over pressure to prevent boiling of the acids. If sealed, CO2 is added to reactor.
> 
> Rh in the tube is done in 30-60 minutes.
> 
> Check out the ultraclave. For Rh for plating solution quantities (say 20 g per hour) it may be all you need.



I did find the ultraCLAVE, it seems great, but 6 figures after customs tax and everything will be in the 7 figures range, sucks to be so far away and have high import taxes.

Now I'm modifying my furnace for a 55 mm diameter 300 mm long tube, for the freechemist fusion.

In the future I will try to buy a Cl2 cylinder and try to dissolve the rhodium powder with HCl on a round bottom flask.



Yggdrasil said:


> Thanks again Lou.
> 
> In your initial post you implied that it was not viable to use bisulfate, is that due to price/time or speed and efficiency?
> Bisulfate is cheap and readily available, Sodium Peroxide is hard to get and expensive.
> ...



I never saw this procedure, but I imagine like this:

The sample + acids is added in the quartz or borosilicate tube, the tube is closed with a flame and put in the heating vessel, normally the tube will handle the pressure, but the heating vessel is designed to handle the eventual explosion. Perhaps CO2 is added outside (inside the heating vessel) to diminish the pressure difference experienced by the tube.

They are not flexible.

To my knowledge CO2 doesn't participate, much less Ar or N2

In my view sodium peroxide is used for analytic work when you must dissolve 100% of the sample (otherwise there would analytical error), for other purposes having less dissolution rates are acceptable.


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## Lou (Dec 1, 2021)

The reason for not using CO2 in open digestion is because it will dissolve under pressure in the liquid media and may cause sample loss as it changes phases/states. For open digestion, nitrogen or argon are much less soluble in the acid and can suppress the boiling. The CO2 on closed tubes or N2/Ar on open tubes serves to counter the vapor pressure of the acid mixture and keep the tubes from exploding.

10 mm quartz tubes we would use are here:








10.5x15.8 • Technical Glass Products


The standard length for this product is 4 ft. Custom lengths available.




technicalglass.com





Typically it is 1 to 5 parts red fuming nitric acid to as high a concentration of HCl as possible. 25 mL can be frozen with LN2 and have 1000-500 mg of iridium (or whatever) sponge, evacuate and flame seal the other end.

We like sodium peroxide for analytical and for production fusions because there is no nitrite produced and less waste treatment concerns. In bulk, it's about $15000/ton. Relative to how much RuO2/IrO2/Rh2O3 it can oxide, it's cheap.

For Rh, better off to chlorinate with salt at 700 C to get Na3RhCl6, dissolve that in boiling water, filter unreacted Rh, add KOH, re-filter the hydroxide and either repeat it to lower alkali or dialyze it.

As for bisulfate/pyrosulfate fusions...sure they work, even better when NaCl is added. It's a temperature thing. Very very hot, concentrated sulfuric acid will dissolve Rh black in hours timescale. It's frightening, with lots of fumes but it will dissolve.


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## Yggdrasil (Dec 1, 2021)

Lou said:


> The reason for not using CO2 in open digestion is because it will dissolve under pressure in the liquid media and may cause sample loss as it changes phases/states. For open digestion, nitrogen or argon are much less soluble in the acid and can suppress the boiling. The CO2 on closed tubes or N2/Ar on open tubes serves to counter the vapor pressure of the acid mixture and keep the tubes from exploding.
> 
> 10 mm quartz tubes we would use are here:
> 
> ...


Thanks again Lou, for the clarification.
I'm grateful whenever you share your knowledge with us.

Regards Per-Ove


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## Abdoulapapatte (Jan 23, 2022)

bonjour afin de répondre au mieux à votre question, nous pouvons dire un peu plus sur la forme de votre alliage s'il vous plait, poids quantité forme, pureté analyser au spectromètre recommandé merci.
par la suite je vous explique la meilleur méthode merci


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## Abdoulapapatte (Jan 23, 2022)

Lou said:


> 4métaux, c'est très chaud et très méchant. Nous avons un autoclave C276 de 2 gallons qui atteint environ 5 000 psi. C'est ce qui est nécessaire pour dissoudre l'éponge Ir/Ru via ce qu'on appelle une digestion par tube de Carius. Nous utilisons des tubes de quartz pur, 37 % w/v HCl et de l'acide nitrique fumant. Vous mettez cela dans le récipient, vous l'évacuez, puis vous ajoutez une quantité connue de CO2 du réservoir et vous le chauffez jusqu'à ce que vous soyez sous pression. Ils sont très longs et fins.
> 
> L'année dernière, j'ai travaillé avec ces personnes pour obtenir une méthode pour dissoudre le Ru/Ir, mais nous n'avons pas eu beaucoup de succès à l'échelle de 500 mg et plus, nous devons faire de l'ICP -OES sur une éponge 4N+ Ir et Ru et obtenir le LOD dont nous avons besoin. Rh se dissoudrait cependant, donc je peux dire que c'est Ir>~Ru>>Rh dans la mesure où la résistance chimique concerne les milieux aqueux oxydants/complexants. Méthodes de téléchargement - UltraWAVE - Milestone
> Ils ont un excellent système, mais ils sont près de 6 chiffres et ne font qu'environ 70 % du type de travail dont j'ai besoin. Je me fie généralement au Na2O2 comme marteau de forgeron.
> ...


Hello, you look very knowledgeable in therm and technical knowledge, I am in metals for 2 years and a half and for the rhodium I never had much stock to treat because, except in the catalytic converter, the thermocouple file, the WEEE in small quantity I don't see where to get it but I can already tell you several things and how to get a high grade 85%//95%// or 9985/1000 if you are meticulous, careful and organized in your work, if you work cleanly, avoiding especially to contaminate your glassware during the manipulations, to contaminate your metal (during the melting), or to contaminate your solution (bad respect of the rules.
as said directly on the post, to better answer the question you need to have the weight and the % of the alloy and the metals present.

if the precious metal is gray (platinum) I advise to make a quartation with silver, or lead
ratio rhodium / alloy: 300/1000 see less concentrated (250/1000) ideal
1) shot blasting
2) nitric acid treatment, - ------>filtration, recovery of solids (sludge, bottom deposit)
3) removal of palladium from the filtrate (DMG)
(if no nickel, otherwise muriatic acid before to remove this and other parasitic metals)
4) filtration complex DMG/palladium)
5) take a small portion of the solution in a tube and test the solution for the presence of Agcl,
if Ag is present ------->precipitate with hcl
6) filtration / isolation of agcl.
End of step 1
you still have :
the liquid of your filtration
-isolated agcl
-palladium in sponge (complex dmg)
the rest solid :
trace Aegent?, palladium? and probably (let's assume):
-or,
-platinum,
-rhodium
Step 2:

1) take the remaining solids from the filtration: everything that has not been digested by your nitric acid
2) make aqua regia
3) heat / then filter
4) repeat 2) and 3) as much as necessary.
5)filtration------> , take out and isolate the waste (black sludge, metallic remains).
6)use sodium metabisulfite (SMB FOR GOLD) -----> gold precipitation, rinse with water, rinse with hcl, boil a little, refil, wash with water then melt gold 9985/1000
7) add ammonium chloride in your filtrate (filtered liquid) and finally precipitate the platinum.
8) filtration -------> isolation of the platinum in spongy form.
9) take the remaining liquid, refilter for safety
10) take the liquid (filtrate of the aqua regia from which the platinum has just been removed)
10) put this liquid in a beaker and add zinc powder, stir and like magic the rhodium saved
11) after waiting for a complete sedimentation of the rh particles, filtration
12) wash the rh powder, several times.
13) Rinse the rh powder with reduced hcl acid (20 to 30% hcl /// 70% water) to remove the zinc

I specify here that step 1 and 2 are used if you have a lot of precious metals together.
IMPORTANT ++++
everything depends on the shape of the rhodium and the state of the rhodium:
If you make a 250/1000 rh/aliasing quartation (rh 250/750 cu ) then no problem, the powder will be able to dissolve easily in hot water +++.

If you take pure rhodium powder and put it in the aqua regia, good luck for it to attack ........ it would take forever .......

last useful choice :
3 interesting videos on rhodium refining:


dernier choix utile :
3 vidéos intéressantes sur l'affinage du rhodium : 





**


bonne chance mec
Vincent


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## cGrem (Apr 7, 2022)

Hello,

According to my experience , after precipitating rodium black with pH14+Ethanol , little amount of rhodium can be dissolved with nitric acid or hydrochloric acid. I don't understand why it is, but I verified it with my ICP-OES analysis. Also when you have an alloy of 95/5 Ag-Pt alloy you can dissolve that alloy with nitric acid.

Çağrı


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## orvi (Apr 7, 2022)

cGrem said:


> Hello,
> 
> According to my experience , after precipitating rodium black with pH14+Ethanol , little amount of rhodium can be dissolved with nitric acid or hydrochloric acid. I don't understand why it is, but I verified it with my ICP-OES analysis. Also when you have an alloy of 95/5 Ag-Pt alloy you can dissolve that alloy with nitric acid.
> 
> Çağrı


I observed this behavior only with alloys or mix of PGMs. When we once treated PtPdRh solution with zinc to obtain workable cement - this cement when treated with 65% nitric will dissolve not only Pd but also awful lot of Pt. After 3-4 days at 100+°C it become to dissolve Rh too. 
PdPt alloy with few % of Pt is also easily dissolved in nitric. This I know from processing old MLCCs. Final button of metals is easily digestible in hot nitric. Most commonly, silver is used as collector metal, so the dissolution is a lot quicker and yields are better. With silver, it goes to the solution pretty much by itself.


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## Geo (Apr 12, 2022)

orvi said:


> I observed this behavior only with alloys or mix of PGMs. When we once treated PtPdRh solution with zinc to obtain workable cement - this cement when treated with 65% nitric will dissolve not only Pd but also awful lot of Pt. After 3-4 days at 100+°C it become to dissolve Rh too.
> PdPt alloy with few % of Pt is also easily dissolved in nitric. This I know from processing old MLCCs. Final button of metals is easily digestible in hot nitric. Most commonly, silver is used as collector metal, so the dissolution is a lot quicker and yields are better. With silver, it goes to the solution pretty much by itself.


Did you roast the cemented powder before leaching in nitric acid?


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## Lou (Apr 12, 2022)

That roasting will change its solubility!


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## orvi (Apr 12, 2022)

Geo said:


> Did you roast the cemented powder before leaching in nitric acid?


I never roasted the powders, so I cannot say. Only thing that comes to my mind is that you will sinter some of the sponge and (big MAYBE) create a less reactive material. Just seems logical to me, but it is just a guess.


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## Geo (Apr 12, 2022)

Roasting cemented metal to red heat does two important things that I can think of. It tempers the metal and removes residual acids. It does make most metals more resistant to oxidation. It may help with Pt dissolving in just nitric acid.


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## Pacin (Aug 12, 2022)

Hi, I have a question to all off you. I'm working for 2 years with different tyle of Rh scrap, mostly e-scrap and rhodium plated scrap. In the begin I need to tell I'm not a chemist but simple electric who build few different type of furence and I really like to absorbing knowlege.
All of you alredy know that Rh is tuft to perticipate to metalic form without using a big ammount of acids and it's hard to melt in most of Al2O3 crucibles. After a lot of work I find out that if I get form of Rhodium hydroxide and dissolve most of it in H2O+NaCl we can do the perticipation using simple portland cement and then wasch it few times witch dem water.


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## Yggdrasil (Aug 12, 2022)

Pacin said:


> Hi, I have a question to all off you. I'm working for 2 years with different tyle of Rh scrap, mostly e-scrap and rhodium plated scrap. In the begin I need to tell I'm not a chemist but simple electric who build few different type of furence and I really like to absorbing knowlege.
> All of you alredy know that Rh is tuft to perticipate to metalic form without using a big ammount of acids and it's hard to melt in most of Al2O3 crucibles. After a lot of work I find out that if I get form of Rhodium hydroxide and dissolve most of it in H2O+NaCl we can do the perticipation using simple portland cement and then wasch it few times witch dem water.


This is a procedure I never heard of.
Where did you find this procedure?


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## Pacin (Aug 15, 2022)

Yggdrasil said:


> This is a procedure I never heard of.
> Where did you find this procedure?


I done this by the mystake. Once when I strips the silver plating from my scrap by the electrolysis using salt water and steinless stell cathode i find out that my silver scrap has a Rhodium plating lyer on top becouse it's left the dark yellow sediment before silver plating came off. Then I remember the moment when I use Portland cement to remove impuritys from my beads (after smelting in oxidation flame) on Portland cement all of my Rh was dissapered but on the top of my used cement forms strenge shiny dark grey to black lyer. Then I realize it's make the reaction with the alcali metals from the cement becouse it's contein Mg and Ca minerals. So to the point, after read all liberary about Rh behavior, Rh catalitic proporties and all what I can get about it I came with a thing that Rh need the alcali metal as flux to melt. So if we get the rafined Rh from cementation on Zinc or other method like a hydrazine or formic acid we will go to the step where we melt it. Of corse if we have fine metalic powder and melt it in a vacum arc furence under presure of hydrogen and argon gas we can get success but the solvation for ouer problem has different path. So i take the risk and I add Portland cement to my solution of dissolved Rhodium Hydroxide at 60'C and magnetic stear, adding cement to solution with really small doeses, leave it over night to seatlle and after this wash it few Times with dem water. The XRF mesure on powder after drying showing only Mg and Ca but when I take the quartz+Zr/Al2O3 crucible and melt it with oxy/acetylen torch it's melting smoth and nice whitout taking reaction with crucible and carbon. So in my opinion rafined Rhodium need alcali metals at participation step and then need it at melting step.


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## Yggdrasil (Aug 15, 2022)

Pacin said:


> I done this by the mystake. Once when I strips the silver plating from my scrap by the electrolysis using salt water and steinless stell cathode i find out that my silver scrap has a Rhodium plating lyer on top becouse it's left the dark yellow sediment before silver plating came off.
> 
> *Rhodium plating will come off as very thin shiny flakes.*
> Then I remember the moment when I use Portland cement to remove impuritys from my beads (after smelting in oxidation flame) on Portland cement all of my Rh was dissapered but on the top of my used cement forms strenge shiny dark grey to black lyer. Then I realize it's make the reaction with the alcali metals from the cement becouse it's contein Mg and Ca minerals. So to the point, after read all liberary about Rh behavior, Rh catalitic proporties and all what I can get about it I came with a thing that Rh need the alcali metal as flux to melt. So if we get the rafined Rh from cementation on Zinc or other method like a hydrazine or formic acid we will go to the step where we melt it. Of corse if we have fine metalic powder and melt it in a vacum arc furence under presure of hydrogen and argon gas we can get success but the solvation for ouer problem has different path. So i take the risk and I add Portland cement to my solution of dissolved Rhodium Hydroxide at 60'C and magnetic stear, adding cement to solution with really small doeses, leave it over night to seatlle and after this wash it few Times with dem water. The XRF mesure on powder after drying showing only Mg and Ca but when I take the quartz+Zr/Al2O3 crucible and melt it with oxy/acetylen torch it's melting smoth and nice whitout taking reaction with crucible and carbon. So in my opinion rafined Rhodium need alcali metals at participation step and then need it at melting step. *Remember Rhodium melts at almost 2000C so it would be hard to get it molten even with a OxyAcetylene torch. The missing Rh in the XRF could be a tell, since Rh and Ir are typical false positives.*


I’m pretty sure this is not entirely correct. There might not be any Rh at all.
Lou or others may chime in on this.
See my comments in red.


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