"Bromate Hydrolysis" Revisited

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RaoOvious

Well-known member
Joined
Mar 28, 2012
Messages
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Does any one know exactly what was the total and individual weight of all six pgm's in the experiments conducted by Gilchrist & Wichers in the known article "A Procedure for the Separation of the Six Platinum Metals from One Another and for
their Gravimetric Determination"
 
sure bromate is an oxidizer but I m referring to Sodium bromate here, used in specific hydrolysis of Pd,Rd & Ir thus leaving behind highly pure Pt sol.,those who deal in this know this.
 
I stumbled on the document you are refering to (I think jimdoc posted it in the books forum) and was amazed at the apparent simplicity of the process.

I was wondering if the Pd should be removed first with nitric before starting the hydrolysis, or is it easier to get the Pd out after getting the Pt.

It looks like something ka could do!
 
Hey kad,

The best would be to do it on impure platinum sponge (after precipitating Pt with NH4Cl and reducing it to sponge),although it can also be performed on whole pgm blacks but that would be inefficient.Regarding the weight of individual metals in the specimen,its not mentioned in the published article of Gilchrist and Wichers.

And removing Pd from mixed bag through Nitric is also severely inefficient,there are ample other options to do the task with minimal hassle.

Hint:Drop Pt and Pd through orthodox methods and then go after specialized tools to get high purity.

By the way nice to hear from u after so long,whats going on lately?
 
Hi RaoOVius,

About the subject of hydrolytic reactions in analytical separations of different PGM's from platinum in solution there exist several publications (Gilchrist, Wichers, and others), but the one you mention contains no details about preparation and quantities of individual PGM's dissolved, Pt included, of the solutions to be examined. There are however two important citations of work, done by german or austrian researchers on the subject of combined bromide/bromate-hydrolysis:
Quite recently, Moser and Hackhofer have reported on the separation of iridium from platinum, and Moser and Graber on the separation of rhodium from platinum, by a hydrolytic procedure in which the alkalinity is fixed by the reaction between bromate and bromide ions. This reaction, however, appears to come to equilibrium so slowly that prolonged boiling and digestion is required to complete the precipitation.

L. Moser and H. Hackhofer, Monatsh., vol. 59, p. 44, 1932.
L. Moser and H. Graber, Monatsh., vol. 59, p. 61, 1932.

In my practice this bromide/bromate-hydrolysis became a valuable tool, especially working up Pt/Rh and/or Pt/Ir-scrap of relatively low Rh-, Ir-percentage respectively, aiming for pure platinum. The chemical reactions, formulated for Iridium, are the following:

Hydrolysis: IrCl4 + 4 H2O ==> Ir(OH)4 + 4 HCl. For completion the generated acid has to be neutralized.

Reaction of sodium bromide (NaBr) with sodium bromate and acid forms elemental bromine (Br2).
5 NaBr + NaBrO3 + 6 HCl ==> 3 Br2 + 6 NaCl + 3 H2O. This reaction uses up slowly the acid formed in the hydrolysis-reaction above, while prolonged boiling leads to volatilization of elemental bromine formed, thus driving the combined reactions to completion. Even a great excess of added stoichiometric NaBr/NaBrO3- mixture doesn't matter. If once iridium is precipitated completely, no additional acid is formed, and evolution of elemental bromine stops.

Regards, freechemist
 

Attachments

  • Separation_and_Gravimetric_Determination_of_Pd_Pt_Ir_Rh.pdf
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The most important aspects of bromate hydrolysis are:

1) slow pH rise. Most of the base metals are out before the Ir and Pd start to precipitate. Go too fast and they will not settle well and will retain more of the Pt mother liquor.
2.) constant presence of oxidizer to insure all PGMs in highest ox state.
3.) solution is free of (NO2)2PtCl6 by boil down. If it isn't, you won't effect as clean a separation of the PGMs.
4.) Rinse hydroxide cake with pH 7.5 or higher bicarbonate buffered water.

If the material is over 99% Pt at start, it's possible to just add caustic to the purified solution and then reduce with hydrazine and calcine. Iridium often needs several separations.

For high grade powders (ie 999%+ platinum such as Steve produces, though his is better in some instances), 8M HCl and chlorine sparging are pre-eminent. At 70 C, the powder will dissolve within 6-8 h. I prefer this over AR because the nitroysl complexes aren't there.
 
Lou,

You are a man after my own heart when it comes to Platinum refining (and purity) :) .

I still want to set up a bromine rig one day and give it a go, just to say I did. My biggest problem is too much work and no free time to explorer new possibilities.

Steve
 
lazersteve said:
I still want to set up a bromine rig one day and give it a go, just to say I did. My biggest problem is too much work and no free time to explorer new possibilities.

Same here... i wish we had just few more hours in a day....

Thank you guys for the interesting posts.
 
If I could just log on the dang forum with my computer I would post up a video or pictures of the process!!!!!!


Very frustrated.

Edit language :twisted:
 
Appreciated Freechemist.

The beauty of the work of Gilchrist and Wichers is that inpite of being open ended in tools used(if you look minutely),the core of the subject is accomplished.With slight acute modifications the task can be done even more satisfactorily.

Nice modifications Lou.


Rao
 
An acute observation for efficient hydrolysis is the crucial Ph control which is undoubtedly the most critical aspect.For this minimize the presence of HCL after complete elimination of NOx otherwise much Bicarb would be needed to attain the required PH's,which ultimately would increase the volume of Pt mother liquor,a highly inefficient scenario.

Moist dry the original solution,acidify with minimal Hcl,hydrate and then start hydrolysis.

Rao
 
That's what we do, make a slush of it, add maybe 3 cc conc HCl for every t oz and then 0.6 L boiling distilled water. The bromate is added in three portions. If the bulk of the impurity is other PGM, it is best to add the major portion from 4.5-6.

Done correctly, no flocculant is needed.
 
There is another crucial aspect,always do hydrolysis in two patches,one at PH 6 or around and another at PH almost 8(Because some try to maintain 6 or 7.5 solely,another inefficiency) to get total segregation.Yes if done correctly no need for any flocculant.

There is a post by another member where main deficiency is the magnitude of mother liquor which is highly crude even if one uses a bit high intensity neutralizer such as carbonate.So the thing boils down to the volume of the main liquor and its manageability with ease.

Rao
 
Lou said:
1) slow pH rise. Most of the base metals are out before the Ir and Pd start to precipitate. Go too fast and they will not settle well and will retain more of the Pt mother liquor.
Silver seems to also come out completely before pH 7, which makes this process also useful to super clean gold solutions, before precipitation.
Thanks to all, for all the nice tips.
 
This is OT but can you go into your hydrolytic gold method, HAuCl4.

What base are you using?

I just want to state that no one here should ever add ammonia past pH to gold solutions--a yellow to yellow brown unstable precipitate is formed. Dry, it is very friction sensitive and will deflagrate with great violence and purple smoke. It is NOT a novelty item!


I would imagine KOH doesn't make it, missing the N atom.
 
NaOH
http://goldrefiningforum.com/~goldrefi/phpBB3/viewtopic.php?f=61&t=14808&p=151128#p151128
This does not attempt to separate PGMs with this "gold hydrolysis", because Pt will stay in solution no matter what. This cleans the solution from base metals and silver (main contaminant usually).
 
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