"Bromate Hydrolysis" Revisited

[cuchugold]

Re-reading this thread to reach 3 conclusions: Bromate use is not essential (replace with Chlorine sparging), removing all base metals substantially reduces hydrolisis supervision time, and done properly no flocculant is needed at all.

Q for Lou: Are these conclusions correct?.

Once again, my experience with this process is only a couple of Oz T at a time, and never repeated the exact same process once in the 7 times I've done it. I'll probably never do it again either.

 

[Yggdrasil]

I'm a bit reluctant to post in this thread, but due to relevance, I will do it anyway.
If someone find a better space for it, let me know and I'll ask the mods to move it.

Well here it is:

As a preparation to make my own Sodium Chlorate and Sodium Bromate, I rediscovered this nice thread.
There is however a couple of questions that still hangs in the air.
Chuchugold made 3 "conclusions" he asked Lou to confirm.
As I see, the one about flocculant has been confirmed by Lou and others already earlier in the thread.

The less Base Metals the less supervision and time is needed, seems logical, but is this statement accurate?

Reading between the lines from Lou it seems that any sufficiently strong oxidizer present during hydrolizing will keep the PGMs in its correct oxidizing state and thus keep Platinum in solution while the others will come out as their hydrated dioxides.
Is this correct?
If so, does this mean that Sodium Chlorate can replace Sodium Bromate?
What about Potassium Chlorate/Bromate?

Can an equilibrium complex of Sodium Chloride - Sodium Chlorate substitute Freechemists "preferred" method of Sodium Bromide - Sodium Bromate or is the Bromate the only way to go here?

 

[Lou]

Platinum is so cheap I've not bothered doing a hydrolysis in a long time. Even then, a lot of stuff I see has W, Mo, Re in it so hydrolysis only gets rid of cationic impurities and the other PGMs, to a certain extent anyway.


I never saw Cuchugold question or I would have answered him. As when selecting any procedure, the better part of valor is knowing when the hell to jump ship and do something else.

1. Less base metals means less hold up of platinum in the hydroxides produced by the process. By hold up, I mean you can rinse a lot of assay off but you'll still have Pt in the filter cake. Ordinarily the hydrolysis is like a finishing step done upon the "refinery" Pt sponge made from the precipitation of a salt. It's nice in that in gets rid of PGMs (iridium is hard to remove) and cationic base metals at the same time.
2. The reason why bromate is used is manifold...it raises pH slow and gives more defined easily filtered hydroxides, it removes Ru as RuO4 (heads up fellas!), it also doesn't have that really annoying *** tendency that chlorate has to make chlorine dioxide and y'know, explode or pop. I hate chlorate for that reason. Chlorine gas and (dilute) caustic is the best to use if you're doing hydrolysis on the cheap and have the setup to handle chlorine safely.
3. Don't use potassium anything with platinum unless you want a K2PtCl6 precipitation and other weird crap as the pH goes up.

 

[Yggdrasil]

Thanks Lou.
Enlightening as always

 

[orvi]

Hi
Maybe trivial question to ask... But:

Gilchrist in his original publication describes that pH is measured by series of acid-base indicators (if i remember correctly), precisely describing the slightest color changes.

Solutions of PGMs as chlorides are extraordinarily colored. Mainly in acid and near-neutral pH range, it is difficult to measure pH of these solutions using pH paper strips. I was wondering how experienced guys here determine the pH of the solution precisely.
I have a good pile of various acid-base indicators from prehistoric ages in the lab but missing some that Gilchrist mentioned in his paper.
Is there some trick how to use classic pH paper strips, or you use some specialized strips ? I also have a pH meter in hand, but it does not feel right to test the solution of precious metals (acidic on the start of hydrolysis) with some electrode meter (plating/corroding/deposition of metals on the sensor messing it up).
Maybe it could be sufficient for me to know how to reach pH 7,5 (and be certain that it is pH 7,5), if there are some specialized methods used in industry, which couldn´t be passed to public

 

[goldandsilver123]

I've the same question, what's the proper pH - ORP probe for many specific solutions.

I never spent much time searching for this, but when I measure the pH of concentrated Pt solutions it's clearly visible that Pt is precipitating in the small fiber connection of the probe. I try to limit this by measuring quickly and DI washing after.



It's been quite a while after my graduation, so maybe I’m wrong, but I think it's possible to change the probe electrolyte from KCl to NaCl, probably it will have an offset, but should be usable. Never had time to try this.



Ammonia solutions are another problem, they dissolve the AgCl over the silver electrode and ruin the probe.



And I'm still searching for a probe designed to be immersed in solution 24/7, for the fume scrubber.

 

[Aurumlife]

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.

I have a question. If original material contained gold, so does it have to be separated before hydrolysis? If so, what is the sequence of the reactions in that case? I thought about Sodium Nitrite for gold and copper (partially) as it separates gold well from platinum group. Looking forward to a guidance here. Thanks.

 

[orvi]

Gold will stay in solution to the quite basic pH, I think that above 7 as well. So it won´t be removed by hydrolysis. You will need to drop it first, but you will need to plan the drop as quantitative as possible. Otherwise it will be carried with platinum. Selection of reducing agent - I will opt for one that won´t make trouble in the next steps. In the case of nitrite, I will not like to pollute my platinum solution with nitrogen oxides, which will complex with it (and other PGMs as well) and completely alter the chemistry and coordination things. Also, SO2 is able to complex to PGMs, so I will also think about SMB twice. Oxalic acid leaves only CO2 as byproduct, so this can work.

I am just thinking out loud. I never tried to recover PMs (except gold and silver) in 999+ purity, as it added no value to them in my situation.