# Problem with Rhodium refining



## kjavanb123 (Feb 23, 2011)

All,

I am left with this gray mud, which is Rh. I tried Steve methods, adding lye, baking soda, heat nothing happened. I guess I am doing it wrong. How long should i heat the Rh gray mud and concentrated sulfuric acid? How much water to dilute it? i keep adding lye, swirle, but pH doesn't change at all. I tried to search the forum for Rh refining, and got too few answers which seem too complicated. I could get 3g of Pd and 0.9g of Rh from this french made cats, but haven't been able to refine the Rhodium.

Thanks for ur advise
Kev


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## samuel-a (Feb 23, 2011)

how did you drop your pgm's black powder?
how did you dissolve the Pd?

what exactly have you done with the lye, baking soda and sulfuric acid? That sound wrong....


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## kjavanb123 (Feb 23, 2011)

I dissolve Rh gray mud in hot sulfuric acid, it turned dark brownish. I have the pics tommorow. filtered the solution, added lye to it, to reach pH 2, i kept adding and pH stayed at 1. I added baking soda, and all i got was lots of those salt percipitating. I can tell I have dissolved the Rh in acid using stannous. but is there any other chemical to add to the Rh solution to drop it?

pgm black powder is from zinc percipitation of cat dissolved in AR. I tested the zinc and it has no impurities.

Thanks
Kev


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## Lou (Feb 23, 2011)

You're not adding enough base. 

Dilute the volume of the acid and add base. pH is too low.


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## Irons (Feb 23, 2011)

Use less Sulfuric next time. Since the solution is dark brown, I would think there is still some Pd in the solution.


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## kjavanb123 (Feb 24, 2011)

ok this is what happened so far with Rh percipitant in pictures.

I tried small quantity of Rh into a quartz dish with minimal amount of sulfuric and heat this is what I got



The same solution filtered into a small beaker



The filtered residue to be tested for more Pd or Rh, and the Rh solution diluted with water.



I left it there, so what to do now? so far is it ok?

Thanks
Kev


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## lazersteve (Feb 24, 2011)

I'm going to update my reply to your original thread here as you have been starting a new topic nearly everyday on the same line of questions and it's getting hard to follow, so I'm directing my reply back to your original thread here:

Original Reply to Rh Questions

Now some footnotes:
1) As Lou said, be sure you dilute the red-brown sulfuric acid solution with the Rh in it.
2) Add Sodium Hydroxide (NaOH) until the pH reaches 2-3.
3) Heat and add dry baking soda (sodium bicarbonate, NaCO3H) until pH is 6-7.
4) Slight boil or 30 minutes at pH 7 (check a few time to be sure it does not change). 
5) Cool and collect Rh(OH)3.

Here are some photos of the various stages of the footnotes above:

1) Red-Brown sulfuric acid:






Please keep track of the amount of sulfuric acid you use. 1 mL of 18.4 Molar 98% H2SO4 (concentrated sulfuric acid) contains 0.0184 moles (18.4 / 1000) of H2SO4. 

The equation for lye (NaOH) plus sulfuric acid (H2SO4) is:

2NaOH + H2SO4 --> Na2SO4 + 2H2O 

Notice the OH from the lye combines with the two H from the sulfuric acid, this is what changes the pH. Since the above equation is balanced, the pH is neutral or pH 7.

Now some math:

2NaOH =~ 80g 

therefore we need 80 grams of lye per mole of sulfuric acid to make the pH 7.

Since we know the molarity of concentrated 98% H2SO4 is 0.0184 moles per mL we can theoretically determine how much lye to add to make the pH 7 by multiplying 80 times the number of milliliters of H2SO4 we used to dissolve the Rh.

For 20 mL of H2SO4

80 g/mole x 20 mL x 0.0184 moles/ mL = 29.44 g of NaOH to neutralize 20 mL of H2SO4 to pH7.

The solubility of lye is about 1.1 grams per milliliter, so we need to add an amount of water in mL equal to the weight of the lye required or about 30 mL to keep everything dissolved. Add the acid to the water, not the water to the acid.

The directions given state to bring the pH to around 2-3 with lye so we won't need the entire 29.44 grams of lye, this number was calculated to give you an idea of how much lye you would need at an absolute maximum when performing the reaction.

Here's a photo of the pH tests at various stages of the reaction:






The pink strip on the left is the original test of the acidic diluted red-brown solution. 

The orange strip on the right is the correct color of the strip after approximately 20 grams of lye was added to the diluted red-brown solution. I started with 20mL of concentrated red-brown solution. You can see the diluted solution after the lye additions in the background of the photo above. 

Here's the solution boiling while I'm adding the sodium bicarbonate (NaCO3H):






and the photo below shows the pH test at the finish point of the neutralization reaction adding the NaCO3H:






The test strip (yellow-green) on the extreme right of the photo is the one after the bicarbonate additions are completed.

Only a few pinches of bicarbonate were required to complete the neutralization. 

If you find you have added too much lye or bicarb, simply add a drop of 1 molar sulfuric acid solution to bring the pH back down. 

Once the pH stays at 6-7 for 10 minutes of boiling, stop adding NaCO3H and gently boil another 30 minutes before cooling.

More later.

Steve


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## kjavanb123 (Feb 25, 2011)

Steve,

Thanks for your help and patience, the level of detailed explaination you go through for all of us interested in pgm refining is just unheard of. Thanks and keep you updated with Rh refining with your complete guidelines.

Kev


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## ashir (Aug 18, 2018)

very informative steve! i have a question , can i use only NaCO3H to get the pH 7? without using NaOH?


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## Iridium chaser (Dec 25, 2018)

Well,strange way to deal with rhodium..The best way to deal with cat converter material that I use since I first heard about that is by smelting dry and just crushed and roasted material with the stuff called oxone!It is sold as pool chemical under the name Aquarius oxy-sparkle!it is containing 65% of potassium peroxomonosulfate(KHSO5),20%of potassium hydrogen sulphate(KHSO4)and 15% potassium sulphate K2SO4! So it's only disadvantage is that it is quickly destroying almost any vessel that you dare to do that in-but obviously there are enough ways to minimise the vessel destruction like covering with lead or better gypsum..Anyway it is always very fast and perhaps the only way to convert every single milligram of all PGMs in their soluble forms,and unlike the aqua regia method it will consume rhodium even faster than platinum but eventually they all will be quite quickly converted!So after cooling you just wash everything with enough water to dissolve the solids,and all your PGMs will be recoverable from the filtered solution(all the insoluble stuff is not containing any PGMs and is only suitable for thermite fun :lol: )..So if someone needs-I can describe the further steps but it is really the same thing as you needed to do after converting all your material into the mix of sulphates of all PGMs plus some impurities that are trivial to dispose of!


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## kjavanb123 (Dec 25, 2018)

Hi Ir chaser

Have you tested this? Do you know the recovery rate using this method? Thanks


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