Simple method of parting Platinum from Rhodium from thermo couple wire

[Marv the assayer]

Hello Everyone, I am Marvin Tanner, owner of Gem State Gold and Silver in Boise. I am new to the group. Can someone share a very simple way to part Platinum and Rhodium from wire that is 93% platinum and 7% Rhodium? I have 13 ounces of the wire and the refineries lose , steal, or are just incompetent with Rhodium. Thanks, Marvin

 

[Lou]

Unless it is type B thermocouple (pure Pt vs less dense leg of Pt80Rh20)) it is unlikely to be that high in Rh. Most of the more common Type S has a leg that is only ten percent Rh.

To separate it, I have found it’s easiest to alloy down with more platinum, melt it and flatten it and then dissolve it in HCl/Cl2. The Rh colors the otherwise orange Pt solution red and can be separated as nominally “Rh(OH)4” from the neutral boiling solution left from bromate (or hypochlorite) hydrolysis. At that point, that’s where the real fun beings as it needs separated from residual Pt and base metals.

Anyway, presume you separate it. What then? Rhodium isn’t exactly easy to sell.

From the refiner’s perspective (having refined a lot of TC wire), I’d say it’s a lot of work that most “refiners” sub out to companies that do Rh it on the regular. They aren’t actually refining it, but someone is,,,

 

[Pen Cen]

please help me

 

[Pen Cen]

Unless it is type B thermocouple (pure Pt vs less dense leg of Pt80Rh20)) it is unlikely to be that high in Rh. Most of the more common Type S has a leg that is only ten percent Rh.

To separate it, I have found it’s easiest to alloy down with more platinum, melt it and flatten it and then dissolve it in HCl/Cl2. The Rh colors the otherwise orange Pt solution red and can be separated as nominally “Rh(OH)4” from the neutral boiling solution left from bromate (or hypochlorite) hydrolysis. At that point, that’s where the real fun beings as it needs separated from residual Pt and base metals.

Anyway, presume you separate it. What then? Rhodium isn’t exactly easy to sell.

From the refiner’s perspective (having refined a lot of TC wire), I’d say it’s a lot of work that most “refiners” sub out to companies that do Rh it on the regular. They aren’t actually refining it, but someone is,,,

Lou!!
Can you help me more?
I completely dissolve TC/ Wire in HCl and H2O2; Now my solution is perfectly very clear and concentration!!

for test !! I add NH4Cl and precipitate Pt but this method doesn’t work 100% because some of Pt doesn’t precipitate and some of Rh precipitate with Pt !!!

again for test I add KCl and precipitate Pt but this method doesn’t work 100% because some of Pt doesn’t precipitate and some of Rh precipitate with Pt

can you help me and say how can I precipitate my Pt 100% without precipitate any of my Rh?

 

[Lou]

You can't get 100% Pt precipitation without taking some amount of rhodium. There will always be a modicum of Pt entrainment and vice versa. There's another thread, that orvi is posting in, where he details some of the same issues you are having except he is having it from a catalyst leach solution that contains Pt/Pd/Rh. I have trouble believing H2O2 and HCl alone were able to dissolve TC wire... usually that is taking quite a while and best done in refluxing AR or in HCl/Cl2 for a while.

We can talk about it here or we can talk about it there but the gist of it is this:

ammonium hexachlororhodate is much more soluble than ammonium hexachloroplatinate especially if the solution is not hot or boiled (it can pickup a water molecule and then its much less soluble and more contaminating of the platinum salt) Often times, the precipitate from Pt with Rh in it has a dirty greenish coloration.

Traditionally, what many people find easiest is to precipitate the platinum rhodium solution with a gross excess of ammonium chloride solution. The filter cake of ammonium hexachloroplatinate gets rinsed with a 5% wt ammonium chloride solution with a bit of HCl added to make it acidic. The bulk of the Rh stays behind in the mother liquor. A very good precipitation will leave maybe 70-100 ppm Pt in the mother liquor with probably 96+% of the Rh staying in the liquor. The ammonium hexachloroplatinate can be dissolved back into solution with aqua regia, evaporated into a syrup and then treated with hypochlorate/bromate/whatever to remove traces of the other PGMs. In this way, a pure platinum solution can be produced and a platinum contaminated rhodium stream can be concentrated.

Hate to say it, but when you have mostly Rh with traces of Pt, the best bet is to make it 6 M in HCl, add peroxide, reflux it and then extract away the Pt with tributylphosphate/kerosene leaving the Rh behind in the aqueous as the unextracted [RhCl6]3- Then the Rh can evaporated down, digested in ammonia that salt filtered off and then worked up in the usual way to high purity.

 

[orvi]

Why you want to refine ? Just for the process or for premium ? I was struggling with selling low Rh material, so we needed to figure out how to bring the content from 0,5-2% to >15% in melt. It took one yeatr of my research on how to do it at sane ammount of steps and overall effectivity more than 93% to the enriched fraction. Yes, it could be certainly done very elegant way, and all PGM industry will laugh at my approach straight away... But with practically no exact informations from the literature or other sources, such as this forum, I am actually proud that I achieved it.

Refining Rh to more than 99% purity to chase premiums is another league to do right, and not in very complicated way. Yes, you can relatively easily make 99% Rh with traditional and conventional methods, but the overall efficiency of the process is not great. Espetially if you start with low Rh feed, as I was struggling with (0,5-2% Rh in PtPd). You could easily end up in several concentration and retrieval cycles to get the content up to 20% from startin 1%. Very tiring to do it only with ammonium chloride, altough it can be done.

Sharp separation could be done with hydrolysis. Oxidative conditions and enough boiling can produce nice packed precipitate. But this become tedious if the content of Rh gets higher - big big volume of voluminous precpiptate, sometimes harder to filter, but essentially OK.

If you are more interested in NH4Cl method, be aware of partial hydrolysis, as Lou mentioned. Platinum and rhodium in solution have both octahedral coordination sphere, where Cl anions could easily replace with OH or H2O ligands. If you do this only in plain water, non-acidified, you can easily loose the Cl ligands (as all complex molecules are in equilibrium in presence of other ligands - here, it is water) and make Rh less soluble. Also Pd behave similarly. On the other hand, in more concentrated acid solutions, separations are much less sharp and drag of other PGMs with precipitate is much bigger.

Lou described much more user friendly process how to do this. You will always be left with some mixed fractions of this and that, that need to be resolved, or better added to another batch. This is most tedious thing in my opinion, processing all various fractions of various ratios of PGMs contained, in various chemical forms (metal ppt, salts, oxides, chlorocomplexes...).
That is where skilled chemist must optimize the process of refining to cut the ammount of mixed fractions and cut the number of operations to minimum to save precious time.

With PGMs there anr numerous methods of purification and extraction, conventional precipitations, solvent extractions, selective resins etc. There is immense number of possibilities how to combine the steps required to afford 3N metals at the end.