Sciencemadness Discussion Board

get RHODIUM out of glassware

wildrebe - 21-3-2011 at 05:29

Hi, I am using a heterogeneous rhodium catalyst for my experiments. There is still catalytic activity left after washing in a lab washing machine (acidic and neutralizing step). To get the rhodium out, I also tried:
- aqua regia
- concentrated sulfuric acid
- sulfuric acid with NaCl
- base bath
Nothing really worked. What else can I try? How about :
- NaCl through which Cl-gas is bubbled?
- sodium bisulfate?

Thanks for suggestions!

Bot0nist - 21-3-2011 at 05:41

I would say the extended washes with warm aqua regia would be the best bet. You will probably just have to give it some time for the acid to work. Maybe change out the acid for fresh a few time.

madscientist - 21-3-2011 at 05:45

From Cotton's 6th edition of "Advanced Inorganic Chemistry":
Quote:
Rhodium and Ir are extremely resistant to attack by acids, neither metal dissolving even in aqua regia when in the massive state. Finely divided Rh can be dissolved in aqua regia or hot concentrated H<sub>2</sub>SO<sub>4</sub>. Both metals also dissolve in concentrated HCl under pressure of oxygen or in presence of sodium chlorate in a sealed tube at 125-150C. At red heat interaction with Cl<sub>2</sub> leads to the trichlorides.


What was your catalyst? What reagents were used? More information may help us devise a solution.

wildrebe - 21-3-2011 at 06:21

The catalyst is rhodium on powdered aluminia, my experiments are in water, reagents are 100uM of organic (bromated) compounds. I am only using about 1mg of Rh per L, so the Rh residues in the glass bottles are rather small. I was hoping to get the rhodium out with a solution not too expensive and not too time consuming, as I would be using (and cleaning) 2 bottles per day..

DJF90 - 21-3-2011 at 08:37

You might want to try hypochlorite bleach?

hkparker - 21-3-2011 at 14:43

Quote: Originally posted by DJF90  
You might want to try hypochlorite bleach?


Exactly what I would say. NurdRage did a video about how Ruthenium would only dissolve in bleach (not even hot conc. aqua regia), so rhodium might be the same.

http://www.youtube.com/watch?v=H7Ng4sOVkns

Fleaker - 22-3-2011 at 21:58

Bleach will not work.

Madscientist basically gave you your options.

Rhodium black and rhodium sponge both dissolve in aqua regia but it should be hot ~80C. I've recovered rhodium off its alumina support before using aqua regia, and using SO2/Cl2 in a quartz tube c. 850 C.

You must use refluxing sulfuric acid to dissolve it--this is what I use when preparing it for making a plating solution, or when I refine it. If you're not seeing white fumes, you're not hot enough. It will go brown when it begins to dissolve (presuming no organic matter remains, but even then, that will be oxidized by the hot sulfuric). It goes to a red solution in aqua regia.



wildrebe - 23-3-2011 at 07:39

thanks fleaker, you were right, bleach does not work. I'll try hot aqua regia. Can I reuse the aqua regia a couple of times or is the reaction finished when it has turned red?

Fleaker - 23-3-2011 at 09:26

Well, aqua regia turns red-orange on standing anyway due to the NOx produced as the NOCl decomposes...

I suppose you could also just wet the glass with water then sprinkle NaHSO4 on it. Heat that very hot until it forms pyrosulfate and it'll dissolve the rhodium giving a deep red color (hence the "rhod" of rhodium)