Dissolve Gold With H2SO4 and H2O2 Peroxymonosulfuric Acid

[kadriver]

Has anyone ever tried this experiment: dissolve gold in hot sulfuric acid and hydrogen peroxide?
Thank you
kadriver (sreetips)

 

[Stibnut]

I've never tried that, but I have made piranha solution (another name for this) before and used it to get black organic crap off of lab glassware. It's such a powerful mix that it oxidizes any organic gunk or even graphite all the way to CO2. I imagine it would work for gold, but I'm not totally sure because the mix doesn't have anything that forms a good complex with gold, the way chloride does. The redox potential of H2SO5 is high enough (+1.8 V IIRC) that I expect it would put gold into solution as a sulfate anyway but I don't know for sure.

It's extremely dangerous, obviously, and I wouldn't recommend it over AR for anyone who has nitric. Of course you're very careful so I doubt you'll have any problems, but I would worry about other people seeing your video and trying it for themselves.

Add H2O2 in small increments to the acid rather than the other way around, which is the reverse of the usual order you'd add acid to water. Addition is extremely exothermic and the additions may locally boil and spatter a bit of acid, but this is better than potential explosions if you do it the other way. Don't exceed a 3:1 ratio of H2SO4 to 30% H2O2 as the mixture can be explosive if stronger in H2O2. Keep any organic solvents far away.

 

[Lou]

Caro's acid has no synthetic use insofar as gold refining is concerned.

You end up with gold in much finer particle size. Probably a mix of Au2O, Au2O3, Au(OH)3.
If evaporated to dryness in concentrated sulfuric, gold (II) sulfate is obtainable.

 

[orvi]

Caro's acid has no synthetic use insofar as gold refining is concerned.

You end up with gold in much finer particle size. Probably a mix of Au2O, Au2O3, Au(OH)3.
If evaporated to dryness in concentrated sulfuric, gold (II) sulfate is obtainable.

Evaporating to dryness from concentrated sulfuric acid sounds like a lot of fun

First time hearing about gold in +II oxidation state. Very interesting.

As you say, too unstable, too uncompatible with anything and too unpredictable. For cleaning dirty glassware - choice of last resort. For refining... no.

 

[Stibnut]

Well, you've done the experiment now and it was pretty cool even if you didn't get what you wanted. Interesting that it didn't dissolve but also didn't break into smaller particles - quite the opposite in fact, it glued itself into three larger chunks. I had wondered before Lou set me straight whether sulfate would complex with it a little bit to put it in solution, or whether the high redox potential of Caro's acid would overcome the +1.5 V of uncomplexed Au(III) and put it into solution despite the lack of a complexing agent.

For Lou and anyone else who would know, under what conditions can gold be put into solution without something to form a decent complex with it? Do you make the hydroxide by adding NaOH to HAuCl4 and then hit it with something like perchloric acid?

edit to add youtube link:

 

[slsmp40]

Evaporating to dryness from concentrated sulfuric acid sounds like a lot of fun

First time hearing about gold in +II oxidation state. Very interesting.

As you say, too unstable, too uncompatible with anything and too unpredictable. For cleaning dirty glassware - choice of last resort. For refining... no.

Evaporating to dryness Piranha solution. Just what you never want to do. As the heat would rise first you would loose the water, raising the concentration of peroxide or causing its decomposition. Do you like the explosion hazard or the possibility of a hot foaming liquid that will literally set your flesh on fire. I don’t think it’s even doable unless you are doing a vacuum distillation. I think it’s safer to work with the cyanide complexes than to purposely concentrate hydrogen peroxide around any metal ions. You know that a fine mesh silver screen causes decomposition extremely rapidly in peroxide. It’s how jet packs work. I wish you luck, but I think you might do better if you just use other chemicals. If an upside exists in this endeavor hell if I can find it.

 

[Yggdrasil]

Evaporating to dryness Piranha solution. Just what you never want to do. As the heat would rise first you would loose the water, raising the concentration of peroxide or causing its decomposition. Do you like the explosion hazard or the possibility of a hot foaming liquid that will literally set your flesh on fire. I don’t think it’s even doable unless you are doing a vacuum distillation. I think it’s safer to work with the cyanide complexes than to purposely concentrate hydrogen peroxide around any metal ions. You know that a fine mesh silver screen causes decomposition extremely rapidly in peroxide. It’s how jet packs work. I wish you luck, but I think you might do better if you just use other chemicals. If an upside exists in this endeavor hell if I can find it.

And you have not even mentioned the sulfuric acid. The Peroxide will decompose reasonably fast, but when will Sulfuric evaporate/decompose and at what temperature. Boiling sulfuric at 330+ centigrade, bad enough at room temperature.
It may be safer to wash your hair in Cyanide solution... Make no mistake, I do not recommend that either.

 

[slsmp40]

And you have not even mentioned the sulfuric acid. The Peroxide will decompose reasonably fast, but when will Sulfuric evaporate/decompose and at what temperature. Boiling sulfuric at 330+ centigrade, bad enough at room temperature.
It may be safer to wash your hair in Cyanide solution... Make no mistake, I do not recommend that either.

It’s funny that you mention that. I didn’t mention the sulfuric acid because I don’t see the distillation of H2SO4 as a hazard. It’s done to purify the acid all the time in a laboratory environment. I know it is actually really dangerous if not done properly, but it’s done safely all the time. You are correct that it is dangerous. But it’s doable. In fact under vacuum it’s almost easy. But you best know your material. If not it will probably teach you to respect it in a not so friendly way.

 

[Lou]

Even under vacuum sulfuric is annoying. It’s very dense and an all quartz apparatus is used.

What I meant by smaller pieces refers to making gold anodic in sulfuric stripping cell.

This reaction Kadriver is trying to show is very left leaning in its reaction equilibria. This is why at or around the Nernst diffusion layer in a gold cell these odd solvated gold species form then decompose into fine gold aggregates.

 

[silver1]

This reaction Kadriver is trying to show is very left leaning in its reaction equilibria. This is why at or around the Nernst diffusion layer

For those that want to understand things more in depth, researching what Lou has posted is a very interesting read.

 

[orvi]

For those that want to understand things more in depth, researching what Lou has posted is a very interesting read.

If person do not have basic chemical understanding, it´s a deep-dive to the universe of complete unknown phase-interfaces... what a field in chemistry.

https://en.wikipedia.org/wiki/Fick's_laws_of_diffusion#Fick's_second_law
This is closely tied to the mentioned topic.

 

[Lou]

It’s a local phenomenon (dissolution of Au by the nascently formed peroxo-sulfate species) and is diffusion-controlled.

The potentials and acidity required to maintain Au in such a state are not easily maintained in aqueous solutions.

 

[Alondro]

It makes the gold powder form lumps... hmmm. You know, this might be a similar process by which gold nuggets are formed in hydrothermal deposits in the first place: highly acidic, high-temp environment with lots of sulfur. Add in really high pressure, and I can see how the dilute quantities of gold in original rock would get cemented together.

Does it look like this might be good in small quantities to make ultra-fine gold stick together... maybe a method to get fine gold out of black sand concentrates by turning it into larger lumps?

 

[Rob2069]

I've often wondered how it would do for cleaning up that black mess you get trying to process IC chips. Ash them grind them up real fine and then pan them out versus turning all of that carbon into CO2 and then just let it drift away in the atmosphere leaving behind some cleaned up gold after all if it can eat a diamond I'm sure it will have no problem with graphite and other less stable forms of carbon and it's about an order of magnitude cheaper than nitric acid besides when you're done can't you just throw salt in it convert it into hydrochloric acid and the addition of much less nitric acid than you were going to use before and be well on your way to chloroauric acid or whatever it is (gold chloride solution)?
Maybe I've just committed another foolish noob error but that's why I'm here isn't it?
And with that l step back and wait for the answer men to fill in all of this stuff I got wrong, and please take it easy on the new guy, as I still have yet to do this for the first time outside of my head. I'm certainly no chemist I never actually finished the 9th grade so big words are fine as long as you explain what they mean and never underestimate the ability and quality of the self education because missing High School effectively just means I missed out on all the social programming everyone else got and I don't consider that a liability at all.
P.S. as far as adding to the atmospheric CO2 levels I'm actually all for that (see what I mean about being deficient in the politically correct / socially acceptable norms LMFAO, or maybe it's just an INFJ thing), but either way I'm pretty good at it (depending on your perspective). Still having a hard time spotting that warming problem historically speaking so I wouldn't worry about it too much and neither should you because I grabbed that screenshot directly from the climate.gov website (go figure), I believe they call that cognitive dissonance or Dunning Kruger effects or even just a severe rectal cranial inversion depending on what you figure the underlined Dynamic is. Now as I'm sure now that I've said more then I should have I will shut up now...

So what do the experts think ???