How insoluble is rhodium in nitric acid ?

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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?
 
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.
 
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.
 
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.
 
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?
 
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.
 
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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