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hydrofluoric acid

Posted by Albert Russ  
G. Evans
Re: hydrofluoric acid
April 10, 2008 02:41PM
As a qualified Inorganic/Organic chemist (BSc/PhD) I find the whole discussion on the use of acid very pedestrian. What I could tell you about the cleaning products you find under the kitchen sink would scare the pants off you, and most would make go down to the local stream to wash by beating their clothes against a tree. Every chemical based substance you can buy at the supermarket, petrol station or drug store has the potential to cause great harm. As a chemist, now retired, I lived with these risks every day and used substances more lethal than the common mineral acids. Most kids get to use hydrochloric, nitric and sulphuric acid by the first year of senior high. The issue is reasonable risk and safety. Use gloves, safety glasses and a well-ventilated area. Do a web search on undergraduate chemistry courses, most Universities have lots of practical info available for download, consult a text like Vogel and go and speak to the Science teacher at the local high school. Can I guarantee that all will go well, well of course not, no more than when I say goodbye to the wife when she goes shopping - accidents do happen, common sense and knowledge will always help to minimize the risks.
Re: hydrofluoric acid
April 14, 2008 03:57AM
What about ammonium bifluoride? I have crystals of hubnerite coated with quartz that would be quite attractive if the quartz could be removed. What safety precautions should be used with this chemical? How effective is it? Will it remove kaolinite? Will it dull the quartz crystals?

Any help would be appreciated.

avatar Re: hydrofluoric acid
April 15, 2008 09:19AM
If the coating of quartz on your hebnerite is very thin, ammonium bifluoride may do the cleaning you desire, but if it is of any thickness you will need to consider that perhaps only hydrofluoric acid will clean it properly. Most if not all of the hubnerite specimens from the Adams mine have been treated in HF to remove the natural quartz coating. Also most of the twinned ferberites from the San Cristobal mine in Peru, have also been treated in this fashion. I don't think you are going to find anyone on the board here willing to discuss the use of this acid for cleaning with you on line. If you can demonstrate that you know something about chemicals and proper safety procedures, contact them off the list and make a good clear case of what you want to do, I think there may be knowledgeable people here that may be willing to discuss it with you. The liability issues are considerable.
Re: hydrofluoric acid
April 16, 2008 03:27AM

I'm neither qualified nor equipped to work with HF. That's the reason for my interest in ammonium bifluoride. I have some amethyst scepters with a coating of some kind of thin, but dulling silicate that would benefit from a cleaning in addition to my hubnerite. Additionally, I have some quartz after calcite rhombs to six inches that are coated with something that dulls them. Maybe. They may be etched by Hf from dissloved fluorite in that vein, I'm not sure. Trying ammonium bifluoride can't hurt. But what are the safety ramifications. I live at the end of the road in the San Juan Mountain foothills with plenty of open space, for what that's worth.

avatar Re: hydrofluoric acid
April 16, 2008 04:11AM
Open space is not the issue here. It is what HF can do to a person's body in very short order. Proper equipment and training is needed to be sure you aren't an EX-mineral collector.
avatar Re: hydrofluoric acid
April 16, 2008 01:51PM
Ammonium bifluoride isn't much safer than HF. See MSDS (especially Potential Health Effects):
avatar Re: hydrofluoric acid
April 16, 2008 03:58PM
Fluorine ions are not referred to as the "Tiger of Chemistry" without reason. Fluorine in it's free state is EXTREMELY reactive and anything that provides it has the potential to severely damage human tissue. The insidious thing about the process is that one is one aware of the exposure until after the damage has been done. Even if you don't manage to hurt yourself, if you do not understand the chemical reactions involved with what you are doing, there's a very good chance you could damage or destroy your specimen in the process.

In actuality, most coatings on mineral specimens are best removed by mechanical means, i.e.: an air abrassive unit. Yes, they cost money, but what is your health and safety worth? Unless someone is an experienced laboratory chemist, I would strongly recommend staying away from chemical cleaning and investing the money on one, or paying someone who has one to clean your minerals for you. A less expensive, thouth not nearly as effective alternative is a high pressure water gun.
Tom Eden
Re: hydrofluoric acid
September 21, 2008 12:01PM
My problem is that I have gold jewelry which is not marked to identify its K.
I'd like to seperate the gold from its accompanying alloys (if any) and was told to
soak it in HNo3 for about a week. I was told the HNo3 would dissolve everything
except the gold. Is it really that simple? Or is there other things involved?
Re: hydrofluoric acid
September 21, 2008 06:23PM
The alloying elements used in gold jewelry are all soluble in nitric acid. However, if the gold is reasonably pure, the metals on the outside might dissolve without leaving enough pores for the acid to reach the inside, and so it might take a really long time to remove all of the other stuff. If there is not a lot of gold, I would imagine that this method would work well: a similar process is used to make Raney nickel from a nickel-aluminum alloy.

One common method (Wohlwill process) of purifying gold is electrolytic, but you need pretty pure gold to start with, and gold chloride for the electrolyte.

I found a patent describing an electrolytic process using ammonium chloride as the electrolyte. If it works, this seems like the best method.

With either dissolving or electrolytic methods, the gold that you get out will be finely divided (powder) rather than a solid mass. In either case, you might also want to consider reprocessing the solution to recover silver and (if you process white gold) palladium. Silver can easily be removed as the chloride with the addition of sodium chloride solution or hydrochloric acid (remove the gold before adding any chloride, or you will get aqua regia, which will eat the gold; adding chloride will also precipitate lead, but this shouldn't be present to any large degree).

You might also consider cuppelation - a method that involves blowing chlorine gas over molten gold is used industrially, but would obviously be very dangerous and nearly impossible to do without specialized equipment.
avatar Re: hydrofluoric acid
September 25, 2008 09:21AM
Thought you description of the various acids was quite good. Why don't you turn it into an article that we could post in the sticky message at the top of the Cleaning bulletin board? My experience in using HF on cleaning specimens is not extensive, but I will be glad to share what I know off line.

Rock Currier
Crystals not pistols.
Re: Regarding Original Post about HF
January 02, 2009 05:10PM
Albeit an amateur mineralogist, I have a persistent question regarding the nature of this particular thread.

What is the motivation behind all the authors who insist on publishing their own sometimes rational, sometimes irrational fears, INSTEAD of answering the original question, which had to do with

*) How to properly or effectively use HF in the structural & artistic transformation of Silicon Dioxide in the form of Quartz?

It seems obvious to me, and perhaps the original author, that HF is available to whomever seeks to find it. That being the case, it seems that one stern warning is enough, and I have faith enough in OSHA labels that this warning is already apparent to the buyer.

So do I really need 75 or more posts telling me about the dangers, some real and some made-up?

Sharing a humorous tale from my childhood - My sister was a chemistry professor when I was a child. I quickly, through charm enough of my own, grew to be very adored in the lab where she worked. The chemistry director befriended me especially when I said I always wanted a chemistry set for christmas. Instead of a lousy rusty-boxed set, I ended up receiving lab chemicals from the department, in boxes. I remember, probably to the ghastly vehemence of most of the fishwife posters here, playing with hydrochloric acid, sulfuric acid, ferrous cyanide, mercury (yes, the shiny liquid metal), along with countless others. The most delightful, now that I read this entire board, yes, was the infamous 'HF.' I'm not denying that I may be alive for very miraculous causes, however, I sit here wondering how many of the authors realize that one warning is enough.

I enjoy the memories from my past, I enjoy remembering the conversations I had with very intelligent and kind professors who taught the dangers as well as the beauties of science, so that I didn't act afraid, but was taught to think and act responsibly.

If you ever remember being a child, explaining what you know about a subject may prove the more appealing offering. One plays with minerals from curiosity, and even though some cats have unfortunate experiences, it seems like the original authors on this board are seeking to temper their curiosity with knowledge, not fear.

Franz Neuhold
Re: hydrofluoric acid
January 02, 2009 06:09PM
Dear Miko!

Yes, we need 75 or maybe more posts on this issue. Your post is an example for irresponsibility and arrogance, which can be misleading and very dangerous for other inexperienced people. Your main argument is that you are not dead. This does not convince me.

In my opinion it is careless and stupid to give HF to a child or use it outside a lab with the necessary facilities.

Best regards,
avatar Re: Regarding Original Post about HF
January 02, 2009 06:17PM
Perhaps it is because not everyone who wants to use HF to etch stuff out of quartz has a background in chemistry, nor toxicology, nor hazmat response, and especially because not everyone reads the included Material Safety Data Sheet (or can understand it).

If you wish to get nekked and roll around in plutonium, feel free. My ethical obligation (if any) ends with pointing out that its probably a very imprudent think to do. However, if I explain to you how to get plutonium, or how to roll around it in, the current legal climate can result in my facing potentially serious legal consequences. (I ain't saying its right, I'm just saying its so. I much prefer the simpler logic of Natural Selection... anyone who wishes to get their Darwin Award, the line forms on the right! Apply early, and apply often!)

You say "If you ever remember being a child, explaining what you know about a subject may prove the more appealing offering." This is precisely why harping on the safety issue involved in HF is important.
avatar Re: hydrofluoric acid
January 02, 2009 11:44PM

> I'm neither qualified nor equipped to work with
> HF. That's the reason for my interest in ammonium
> bifluoride.

You need to take the same precautions with ammonium bifluoride as you do with hydrofluoric acid. Ammonium bifluoride is less reactive and less prone to produce fumes, but perfectly capable of causing tissue damage. I believe Rock is right and that this boards suffers of too much fear mongering with respect to chemistry.
But you do the right thing, ask for advice, when you don't know. Until you have a good understanding of chemistry and working experience with other chemicals, I recommend you for not use hydrofluoric acid, nor ammonium bifluoride.

That said, both have their proper use but more often than not, specimens are ruined. When you visit mineral shows, you invariably see Chinese and (particularly some years ago) Pakistani & Afghan specimens that got the good old hydrofluoric acid rinse ... and were completely ruined.

All the best


Claus Hedegaard
Google me to find me!
avatar Re: hydrofluoric acid
January 03, 2009 10:33PM
When I worked for a manufacturer of clinical analysers, we routinely needed to etch the glass membrane of one of the ion-selective electrode assemblies. The reagent used was a mixture of an acid and a fluoride (and no, I'm not saying which). The concentration was the lowest that would do the job and the bottle size (150ml) was calculated to be less than the F25 for adult human (i.e. consumption of the bottle would kill less than 1 in 4 people).

Shall we say that I have a healthy respect for any soluble fluorides.

When you invited me to see your etchings, I didn't expect to
see so much degraded quartz. Really.
Re: hydrofluoric acid
March 22, 2009 12:38AM

In household detergents? One hopes they are combining it with something else to make a final compound other than HF but, in that case, why not do it at the source, to eliminate the need for moving tons of HF along the public roads?
avatar Re: hydrofluoric acid
March 27, 2009 01:43PM
"Whoever believes in everything he's reading should better stop reading at all."

A newspaper article is certainly not the best source to learn something about chemistry. Whatever they wanted to say, they screwed it up.

It is true that HF is used as a raw material in the synthesis of particular surfactants (perfluorinated surfactants). Surfactants, on the other hand, are used in a whole array of different products, among which also are household detergents (note that a detergent is defined as a formulation that contains a surfactant). It is not true, however, that these particular surfactants are used in household detergents. Perfluorinated surfactants are chemically extremely stable and that there is no risk of setting fluoride free in normal use (deliberately burning them would not be a good idea, though). They are toxic, but for different reasons.
So, if you google for products that are manufactured from HF, you may find surfactants. If you google for the applications of surfactants, you probably find household detergents. Linking one to the other may appear logical (well, logics again !) if you don't know that "surfactant" is not a chemical classsifier but just refers to an obscure physico-chemical property that is met by hundreds of thousands of molecules.

HF is also used to produce hexafluorosilicate 2-, which may be used as a disinfectant. Again, hexafluorosilicates are very stable compounds.
Re: hydrofluoric acid
August 17, 2010 10:09PM
I need the complete process of Chemically polishing Quartz crystals, If somebody have the complete process of chemically polish quartz crystals with ,please share it with ammonium bifluoride me.The ratio of mixing ammonium bifluoride with distilled water.
Re: hydrofluoric acid
August 17, 2010 10:47PM
If this polishing you want to do is related to the problem you reported in your other post (ie. lost luster on quartz crystals by overcleaning with HF), then using ammonium bifluoride will only exacerbate your problem, because NH4-bifluoride attacks quartz the same way HF does, just more slowly. Too bad that you ruined the quartz with HF, but that quartz is going to stay ruined; can't put spilled milk back into the bottle.

Edited 1 time(s). Last edit at 08/17/2010 10:48PM by Alfredo Petrov.
Re: hydrofluoric acid
August 18, 2010 03:48AM
Hi all!

Albert,even if you (obviously) are an experienced scientist,you'd better not use it.

I will answer randomly,since many replies are present.

HF burns can be noticed immediately or after a while.The burns are still burns,however,the acid,by absorbing Calcium can attack the neural system and thus the brain cannot realize the pain.

This is very dangerous,since the therapy is delayed.

Calcium gluconate gel is not enough in most case.One needs pills or even injections.It depends on the skin surface attacked.Gel is better than nothing,but not enough.

From my personal experience:

I have a couple of friends who used to use the acid.One of them used to use it with bare hands and no mask.He never had burns dipping his hand to the elbows inside the solution.He suffers from heart failure (probably due to the acid).He has been a miner and a person always living at a fresh air mountain site with healthy food and lifestyle.

The other one used to use gloves but no mask.He didn't notice the glove had a hole and he lost tissue to the bone of his finger.The doctors treated well the necrosis and the tissue was restored.However,no calcium gluconate was applied and he will have some organ failure in the future.

Note that both of them lead a perfect lifestyle!A smoker junk food eater with an office job will have much more serious problems!

Even if an accident doesn't occur,improper equipment will allow the acid to penetrate the skin and lungs and will cause health problem in the future!

All this for removing Quartz.

Even thinking financially,the use of the acid can provide you a good specimen that would be as expensive as 10.000 USD maybe?A laboratory can do it for you for some hundreds of USD.

An accident will cause you health problems that eventually will cost you much more!

I'm not sure if it right not to provide information on using the acid.There are people who won't believe until it happens to them and will use the acid.

Now,Albert,what do you mean by getting an interesting structure?seen specimens treated to remove a second generation and reveal the crystal color,but have you seen the result?Removing Quartz off Quartz?

You say you want to etch to get interesting structure.Do you want to get an etched crystal?What for?

With just a dip in low concentration (2-3 %? I have no idea) you will get the outer surface of the crystal with a look of surface cracking.

This is a fake to me.Removing Quartz off some other species would be ok,but Quartz off Quartz means both generations or crystals will be affected so this as valuable as polished specimen and even uglier!

Please post a photo,so we could understand what you intend to do.


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