Chemical HNO3-HF

[Fijcho]

Hi
I am new to this forum and have a chemical question.
Gold can be dissolved in a mixture of nitric and fluorhydric acids, kind of alternative aqua regia?
Thanks!

 

[FrugalRefiner]

Hydrofluoric acid (aka fluorhydric acid) is extraordinarily dangerous! I would far prefer nitric and hydrochloric acid.

Dave

 

[Topher_osAUrus]

Hydrofluoric acid (aka fluorhydric acid) is extraordinarily dangerous! I would far prefer nitric and hydrochloric acid.

Dave

Yeah, i don't think i would ever entertain the idea of using HF.

Something that a drop, can sneak up on you, unnoticed...then eat away the calcium in your bones so they just snap?

I would certainly pass on that, and stick to the other traditional (still dangerous but *nothing* on hydrofluoric) methods..

I like my bones though...they've never done me wrong yet in 30 years, so i don't want to push it 8)

 

[mls26cwru]

first, hydroflouric is much more dangerous than nitric, so it wouldn't be a 'better' alternative to begin with...

second, I don't think it will work, because in Aqua Regia, its a two part reaction where the nitric attacks the gold and forms an intermediate compound which the hydrochloric come next to react to form chloro-auric acid... the chlorine that hydrochloric provides is a key step in dissolving the gold.

third, if you don't know that HF is a more dangerous acid to use, then you really need to educate yourself on basic chemistry a whole lot more before even think about starting to refine.

 

[FrugalRefiner]

second, I don't think it will work, because in Aqua Regia, its a two part reaction where the nitric attacks the gold and forms an intermediate compound which the hydrochloric come next to react to form chloro-auric acid... the chlorine that hydrochloric provides is a key step in dissolving the gold.

I hate to pick nits, but as I understand it, the nitric acid in aqua regia oxidizes the gold (removes one or more electrons) which creates gold ions (Au³⁺). The nitric does not form any intermediate compound with the gold. The gold ions then combine with the chloride ions (Cl^-) from the hydrochloric acid to form chloroauric acid.

Dave

 

[Fijcho]

Hi fellows

I appreciate your concern about my health and the dangers of HF.
My interest is only academic, but not being trained in theoretical issues about chlorine versus fluorine, I ask your advice.
No plans to do any reaction with HF.
Does anyone have an idea about the possibility to dissolve gold in that mixture?
Thanks!

 

[mls26cwru]

I hate to pick nits, but as I understand it, the nitric acid in aqua regia oxidizes the gold (removes one or more electrons) which creates gold ions (Au³⁺). The nitric does not form any intermediate compound with the gold. The gold ions then combine with the chloride ions (Cl^-) from the hydrochloric acid to form chloroauric acid.

Dave

You are correct... I should have chosen my words a little more carefully... "nitric attacks the gold and forms an intermediate compound" should have said "nitric attacks the gold which puts it into an intermediate state". The nitric doesn't actually combine with the gold and I can see how that could have been misinterpreted with how I worded it. I am pretty sure compound is also the wrong term to use as well since it oxidizes the gold to Au3+ which would still be an element and not a compound.... i hope I have it right now

 

[jason_recliner]

Purely hypothetically then, my advice would be the same as to anyone contemplating the idea of:

- Owning a pet chimpanzee
- Modifying a Honda to look like a Corvette
- Slicing your birthday cake with a chainsaw
- Using an acid so nasty it makes nitric look like dishwashing detergent, when there are simple options.

Just because you can, doesn't mean you should.

 

[Topher_osAUrus]

If your goal is purely to gain knowledge or *academic* reasons. I think that most of the halogens on the periodic table can manhandle gold to some extent. I know ive read of iodine, bromine, chlorine... So fluorine may work too... But, i wouldn't even mess with the idea.

If its plausible, maybe one of our chemists here can hit us with some knowledge

 

[nickvc]

I believe you can use HF and hydrogen peroxide to dissolve gold but can't see many applications where that would be a process of choice, if it were me I'd avoid anything that needs HF and leave it to the professionals who have the right safety equipment to handle the dangers.

 

[Fijcho]

Thanks you all!

 

[Lou]

No, it doesn't work with peroxide or nitric.

 

[Connie Saxe]

I understand this thread is very old, but the interest in the subject of HF Acid never ages. Someone needs to come to the rescue of defending the reputation of HF Acid ........ The drama never ceases when it comes to HF Acid.

As an acid, the primary reason HF Acid is somewhat different is because it is the "lightest" of all acids. The lightness is what makes HF Acid so useful in precious metal refining. If you want to know how the lightness of HF Acid applies to refining, sit down and study the chemical properties of HF Acid and you will figure it out.

I use HF and HF-Silicate Acid all the time and I am still alive and well. If HF Acid was as dangerous as all the Internet misinformation would make it out to be, it would not be sold over-the-counter.

Next if the chemist simply follows basic rules of chemical ingredient handling, all will be well.

I am more fearful of Conc. Sulfuric Acid than any other acid, why? Because Sulfuric Acid can ignite a paper towel and start your trash can on fire if just a slight amount is on the towel and is not properly diluted before disposing of the towel.

In terms of precious metal refining, I find HF Acid and HF-Silicate Acid invaluable tools for among many reasons, in analyzing ore without having to take the hammer and chainsaw approaches of finding out what is inside of quartz. Just throw your sample in the container along with HF Acid - come back the next day, wash away the HF Acid and you've got a complete picture that can be examined microscopically - minus quartz and many disruptive base metals and debris. Absolutely effortless.

 

[Yggdrasil]

I understand this thread is very old, but the interest in the subject of HF Acid never ages. Someone needs to come to the rescue of defending the reputation of HF Acid ........ The drama never ceases when it comes to HF Acid.

As an acid, the primary reason HF Acid is somewhat different is because it is the "lightest" of all acids. The lightness is what makes HF Acid so useful in precious metal refining. If you want to know how the lightness of HF Acid applies to refining, sit down and study the chemical properties of HF Acid and you will figure it out.

I use HF and HF-Silicate Acid all the time and I am still alive and well. If HF Acid was as dangerous as all the Internet misinformation would make it out to be, it would not be sold over-the-counter.

Next if the chemist simply follows basic rules of chemical ingredient handling, all will be well.

I am more fearful of Conc. Sulfuric Acid than any other acid, why? Because Sulfuric Acid can ignite a paper towel and start your trash can on fire if just a slight amount is on the towel and is not properly diluted before disposing of the towel.

In terms of precious metal refining, I find HF Acid and HF-Silicate Acid invaluable tools for among many reasons, in analyzing ore without having to take the hammer and chainsaw approaches of finding out what is inside of quartz. Just throw your sample in the container along with HF Acid - come back the next day, wash away the HF Acid and you've got a complete picture that can be examined microscopically - minus quartz and many disruptive base metals and debris. Absolutely effortless.

Any of the acids we use in refining, are safer than HF.

We at most use 90-98 % Sulfuric for the Sulfuric de plating cell and as long as it is not too hot it is safe enough.
It will not ignite much if at all.
Even drops on your skin will not do much damage as long as it is washed off within a reasonable time.

HF on the other hand is in a different level of Toxic.
As acid it is a weak acid but the "only" that will dissolve Glass/Ceramic.
It has long term damaging effects on bones and soft tissues in the body if you get too much on the skin.

It is how ever a much used Chemical in different industries and is relatively easy to get hold of, at least still at this time.
I believe that if it was replaceable it would have been replaced a long time ago.

One can safely work with it as long as one respect the dangers and use proper protocols for handling and use.
As with much other things we use.

 

[4metals]

In terms of precious metal refining, I find HF Acid and HF-Silicate Acid invaluable tools for among many reasons,

Truth be told you are not actually doing any precious metal refining, you are simply dissolving the silicates to expose more of the precious metals in the sample.

Still it is a nasty, unforgiving, acid and if you are hell bent on using it, keep some calcium gluconate around to neutralize any if it contacts your skin.

 

[4metals]

From what I posted above, it may sound like I am down on using HF in a refinery. Actually that is not the case. I get involved with refiners doing a process called chemical stone removal where the goods are refined in aqua regia by a typical aqua regia process and the stones which are subsequently cleaned and sorted, colored stones from diamonds. At this point an easy way to differentiate the diamonds from CZ's is by using HF. This treatment is also not refining but it helps a sorter to pick out the frosted stones from the real diamonds (and lab grown diamonds) quickly. The HF is used cold and is very effective.

Still that does not stop me from telling the refiners the potential horror stories about HF and what precautions need to be taken. I also strongly suggest they purchase a HF spill kit and a HF burn kit to have on hand. The application I use does not require heat and the actual reaction is not even visible to the eye. Still goggles and gloves are a must.

The biggest screw up I see, despite many warnings, is refiners using the HF on diamonds in a glass beaker. They truly experience a WTF moment when they come back to a beaker which has no bottom and is sitting in a puddle in the hood. HF eats glass! It needs to be used in plastic and stored in plastic. One refiner dumped the spent acid down the toilet bowl and was shocked to see the residual HF ate the porcelain coating and dissolved the toilet bowl in time. Another added it to his waste stream only to find out it also eats the glass calomel pH electrodes controlling the waste treatment. So yeah, the stuff keeps on working. The most effective method I have found to treat the used acid is to have a plastic pail with broken glassware in it to pour the spent acid into and let it have it's way on the glass until it reacts no more. If anyone can suggest an easier low tech effective method I am all ears!

So if you use it, be careful!

 

[Marcel]

Please remember that many members of this forum may lack the proper equipment, handling skills, and awareness of the potential hazards associated with hydrofluoric acid (HF). I seriously doubt that most users are equipped to manage its risks safely. With that in mind, please steer clear of using HF for gold refining. If you have any material—even quartz with microscopic amounts of gold—leave it to a professional refinery. End of discussion. For me at least....

 

[orvi]

I lost my very good friend (chem engineer with PhD and decade of experience) most probably due to HF or any kind of fluoride salt. You are hero until you aren´t... Same with cyanide. Same with myriad of compounds.

I am organic chemist. Working daily with much more frightening compounds than HF or hydrogen cyanide. Compounds with LD50 of 2ppm or lower. I am still alive - does that mean these are harmless ?

There is nothing more effective for cleaning virtually any stainless surface than nitric-HF combo. Would I use that on regular basis to clean my pans and pots in the kitchen ? No. Would I make YouTube short video about how I clean my old greasy pot with HF/HNO3 mix and post it as "life hack" ? No.