Sciencemadness Discussion Board

Concentrating HF solution

Db33 - 7-12-2016 at 17:29

Whink Rust Stain Remover thats available in most grocery and hardware stores is 1-2% Hydroflouric Acid. I was wondering if there is a way to create something like a 40-70% concentrated solution from this? Would boiling away the water help? Or distillation?

j_sum1 - 7-12-2016 at 17:45

This request scares me.

Without a really good and intimate knowledge of HF including all its properties and handling procedures, you don't want to come anywhere near 40-70%

Db33 - 7-12-2016 at 17:52

im just curious, i am nowhere near set up at the moment to do it, but understanding how to do it, nothing wwrong with that. Same thing with Cyanide salts. Im very interested in them however i would never make them and if i did it would have to be in a lab with alot more capablities than i have at the moment. But yeah what would be the process of concentrating the HF?

DraconicAcid - 7-12-2016 at 17:56

1) I agree with j_sum1. HF of any reasonable concentration is nothing to play with.
2) You can't concentrate a solution of HF by boiling off the weater, since the boiling point of HF is so very low. You'd probably be better off mixing a source of fluoride with a non-volative acid and distilling HF from that.....or better yet, finding a safer project.

woelen - 7-12-2016 at 23:48

I also have to second DraconicAcid and j_sum1. HF is one of the few chemicals which really scare me. E.g. if you spill 40% HF on your clothes and more than appr. 100 cm² of your skin is covered, then it may kill you. At least you will have a VERY bad time. Just to get you informed, open the Google search page and type "hydrofluoric acid burn" and select the images of this. Not for the faint of heart!!

Even 96% H2SO4 and 68% HNO3 are child's toys compared to 50% or so HF!

DDTea - 8-12-2016 at 04:36

This is more work than it's worth. Probably the easiest way to do this would be to quench it with CaCO3 or MgSO4, filter, and then react the solids with H2SO4 and distill. Or you could just start with CaF2 or MgF2 from the get-go. But really think it through: how comfortable are you heating up hydrofluoric acid in a glass distillation pot? I'm definitely not.

In my experience, hydrofluoric acid isn't as terrifying as people say but it does require an appropriate setup. I've worked with quite a bit of 50% solutions to prepare solutions for elemental analysis. We used teflon digestion vessels and good fume hoods the entire way. I wouldn't dream of using it without ready access to calcium gluconate gel. And I've heard 70% solutions are another animal entirely. Also, HF gas is about as irritating as chloropicrin. It just causes a faster reaction than the latter, so you can't easily take a big whiff.

I know a guy who spilled some 50% HF on his hand. I looked at him in disbelief, amazed he still had all 10 fingers. "It just hurts real bad, like getting hit on the finger with a hammer." Your luck may vary.

Chlorine - 8-12-2016 at 05:55

I'd highly suggest you stay away from HF, extremely scary stuff. This makes nitric/sulfuric/hydrochloric look like child's play.
If you have to ask the question if it's possible, you don't have the insight necessary to safely handle this chemical.

RogueRose - 8-12-2016 at 06:06

I've always been curious about HF and would only work with it if a train professional were assisting (I was watching). Can it be made like other acids by taking a salt like fluorspar (CaF2) and mixing with H2SO4 to give 2HF + CaSO4?

I know HF can be pretty harsh on some substances so what kind of beakers or containers would be acceptable for HF? I thought PTFE was one of the only substances that resists HF.

ave369 - 8-12-2016 at 07:28

Quote: Originally posted by RogueRose  
I've always been curious about HF and would only work with it if a train professional were assisting (I was watching). Can it be made like other acids by taking a salt like fluorspar (CaF2) and mixing with H2SO4 to give 2HF + CaSO4?


Yeah, in this respect it's just another volatile acid. Use a cast lead retort and a copper coil to distill it. A FUME HOOD is mandatory.

For the topic starter, Whink is enough. Whink is the only form of HF that can be called reasonably safe.

PirateDocBrown - 8-12-2016 at 07:32

As a professional, I have handled HF.

I used a strong fume hood, and was making YbOF2. I double gloved (the top gloves were gauntlets to the elbow), had a splash shield over my face, and wore a smock, rubber apron, and a lab coat.

The fumes somehow got out of the hood. They had a smell like HCl, but a hell of a lot stronger. The impact on my nasal mucosa was ferocious.

I held my breath, set down the work, turned on the room ventilation, and evacuated until it was clear.

I felt like I had been punched in the face.

I never used it in the hood again, dry box only.

Do yourself a favor and don't mess with HF. That shit will kill you.

If you must fluoridate, consider KHF2?

[Edited on 12/8/16 by PirateDocBrown]

PirateDocBrown - 8-12-2016 at 07:46

I remember also seeing video of an experimenter dangling a chicken leg into a vessel of HF. It was left overnight.

By morning, it was as if the leg had been sheared off at the waterline. Bone, muscle, fat, and skin and been completely solubilized, leaving only a stump. On the stump, the vapors had bleached everything to a dead white, like zombie flesh.

HF penetrates the skin, directly attacking bones. It can travel along nerve channels, killing as it goes, until it reaches the heart, when it kills you. Since it kills nerves, you often don't even feel it attacking you. People have lost hands from pinholes in gloves.

I am no slouch, I have handled boranes, molten white phosphorous, liquid cyanogen, and many other kinds of oxidizers, corrosives, toxins, and explosives. I won't touch HF, not if I can help it.

I laughed out loud when I saw it portrayed on "Breaking Bad".

DraconicAcid - 8-12-2016 at 08:24

Quote: Originally posted by RogueRose  
I've always been curious about HF and would only work with it if a train professional were assisting (I was watching). Can it be made like other acids by taking a salt like fluorspar (CaF2) and mixing with H2SO4 to give 2HF + CaSO4?

I know HF can be pretty harsh on some substances so what kind of beakers or containers would be acceptable for HF? I thought PTFE was one of the only substances that resists HF.


Yes. One of my old, old texts has a demo for etching glass with it- take a watch glass, coat it with wax, scrape off the wax from the part you want etched, and use it to cover a plastic beaker holding sulphuric acid and (toothpaste? An old tooth? My memory fails me) overnight.

Amos - 8-12-2016 at 08:42

Treating calcium or barium fluoride with chilled aqueous sulfuric acid and filtering off the precipitate through cotton or polyester in a plastic funnel is a good poor man's way. Unless you have some really solid experience with HF at low concentrations behind you already though, I don't advise you try this. If you've seen how volatile hydrochloric acid is, hydrofluoric acid is only more so, and it doesn't smell terrible enough to convince you you're being poisoned while in vapor form. Do also keep in mind that burns from hydrogen fluoride, whether from the gas or solution, often don't present themselves with pain or visible skin damage until much later. Proceed with extreme caution.

RogueRose - 8-12-2016 at 10:04

Wow, the wax thing is pretty interesting. Is HF one of the most common glass echants or are there better (easier or safer) ones? Could it be used on iron or steel like a steel chain (thinking of dramatic movies where an acid is dissolving away something) to dissolve it away (or minimally to etch it as well). Would there be something better to etch away a fair amount of steel (thinking for some specialty knife/sword work where lasers aren't an option).

PirateDocBrown - 8-12-2016 at 10:25

For metal etching, HF would be a poor choice. The fluoride ion will react with many metal surfaces, creating an unreactive layer.

For either ferrous or cupric metals, a far better choice would be a solution of FeCl3 and HCl.

In glass etching, HF is used, but can be quite dangerous to handle. Much more common is use of hexafluorosilicic acid (H2SiF6). Also used are solutions of various bifluorate (FHF-) salts.

DDTea - 8-12-2016 at 10:26

Quote: Originally posted by PirateDocBrown  

I am no slouch, I have handled boranes, molten white phosphorous, liquid cyanogen, and many other kinds of oxidizers, corrosives, toxins, and explosives. I won't touch HF, not if I can help it.


Come on, seriously? I hear these sorts of statements all the time. They confer a pseudo-scientific mythology to HF that is wholly unnecessary.

In an old gig, I was required to suit up in a Tyvek jacket, face shield, and gauntlet gloves to dispense 10 mL inside a fumehood using a repipettor. They called it "the bird suit." I guess I looked like Big Bird. We had our antidote in what looked like a fire extinguisher, clearly intended for whole-body HF exposure. The instructions said to "use entire container." Pencil-pushing safety officer insisted we follow the instructions to the letter. This would lead to the absurd situation of being exposed to, at most, 1 mL of HF and being doused by a fire extinguisher of antidote. Comparing this practice to other (professional) environments where I've worked with HF, it was totally ridiculous. Can we all come back to Earth?

I don't believe in just being scared of chemicals. I believe in learning the specific hazards, figuring out what's necessary to handle it safely, and making a decision whether a) I'm equipped to do so, and b) there's a better way to accomplish my goal. The place to start is with safe handling guidelines: https://www.mcgill.ca/ehs/laboratory/lab-safety-guidelines/g...

004-1.jpg - 57kB

Amos - 8-12-2016 at 10:40

I agree wholeheartedly. What makes a particular chemical reagent dangerous has more to do with your knowledge and your approach to utilizing it than any other factor. Hydrofluoric acid is definitely something that can be handled at home by an experienced amateur. The tone a lot of us are taking, I think, has more to with the original post and the poster's history on this forum thus far.

RogueRose - 8-12-2016 at 11:51

Quote: Originally posted by DDTea  
Quote: Originally posted by PirateDocBrown  

I am no slouch, I have handled boranes, molten white phosphorous, liquid cyanogen, and many other kinds of oxidizers, corrosives, toxins, and explosives. I won't touch HF, not if I can help it.


Come on, seriously? I hear these sorts of statements all the time. They confer a pseudo-scientific mythology to HF that is wholly unnecessary.

In an old gig, I was required to suit up in a Tyvek jacket, face shield, and gauntlet gloves to dispense 10 mL inside a fumehood using a repipettor. They called it "the bird suit." I guess I looked like Big Bird. We had our antidote in what looked like a fire extinguisher, clearly intended for whole-body HF exposure. The instructions said to "use entire container." Pencil-pushing safety officer insisted we follow the instructions to the letter. This would lead to the absurd situation of being exposed to, at most, 1 mL of HF and being doused by a fire extinguisher of antidote. Comparing this practice to other (professional) environments where I've worked with HF, it was totally ridiculous. Can we all come back to Earth?

I don't believe in just being scared of chemicals. I believe in learning the specific hazards, figuring out what's necessary to handle it safely, and making a decision whether a) I'm equipped to do so, and b) there's a better way to accomplish my goal. The place to start is with safe handling guidelines: https://www.mcgill.ca/ehs/laboratory/lab-safety-guidelines/g...



What, you think making your face white is going to trick us? I know what you look like and who you are!



































004-21.jpg - 20kB



:D

Chemetix - 8-12-2016 at 12:21

HF is worthy of respect, but a 40% soln. is not going to kill you on sight.
I use it occasionally for glass, gloves and eyeware are a must. But the fumes, I avoid them, you can see coming. They make a visible mist and it allows you to stay 'upwind' of them.

Using small quantities such as a pipettes worth at a time poses no real threat to someone using caution. I hate trying to decant from the bottle, that's when I fear something going wrong.

But it does have some awesome qualities, a super aqua-regia using HF instead of HCl chews through Titanium like HCl chews through Aluminium foil.
It left an exposed crystal structure of the metal which gave a fantastic electro-anodised finish. Diluting the acid gave a finer finish and an almost iridescent effect to the anodising.

I don't see that 2% stain remover here anymore now that you bring it up. But concentrating it is an interesting project, maybe freeze concentrate the solution? Polyethylene equipment should be used to work with all concentrations. Staying with small quantities and being appropriately safety conscious shouldn't expose you to its toxic effects.

Fluoride competes with calcium in the body, the comparable ion size is the reason it interferes with calcium channels, heatbeat regulation being dependent on calcium flow is not going to like fluoride ions any any significant quantity. This is what I was told, I'm no biochemist. But even small acute burns are very painful. Depot injections below the site of exposure with calcium gluconate is the only real antidote to preventing more longer term damage.

Also, long term exposure of sub toxic levels leaves you with very brittle bones, or so the anecdotes go from people who told me about working with it industrially. I know this might be a tad long, but know the risks.

BromicAcid - 8-12-2016 at 12:41

Quote: Originally posted by DraconicAcid  
2) You can't concentrate a solution of HF by boiling off the weater, since the boiling point of HF is so very low.
Strictly looking at boiling points you should be able to boil off the HF and collect that.

However HF does form a azeotrope with water so you could boil off the water leaving azeotropic HF behind (~35%). But the issue then becomes the fact that the HF is not going to have a vapor pressure of zero so you will lose HF in the process and since you're only starting at 2% you may not make any gains. That is unless you use a column, but I haven't seen any PTFE distillation columns. Corollary to that is that I haven't looked for one before. At least in that case you shouldn't have an issue finding PTFE boiling stones with which to pack the column.

Bert - 8-12-2016 at 13:13
Quote:
I laughed out loud when I saw it portrayed on "Breaking Bad".


Yep. Walt and Jessie just standing there and looking at the hole in the ceiling from the corroded out bathtub full of the dead gangster guy and hydroflouric acid, like it was no big thing? Jessie, sure. He would have stood there gawping at the hole. Walt was already running, and the next body he had to dispose of would have been Jessie's.

Dr.Bob - 8-12-2016 at 13:27

Having used liquid HF and a few other HF sources, I would avoid if at all possible. I had on huge gauntlet gloves, face shield, and lab coat plus apron. More than once fumes started overpowering the hood, and I closed it and got out of the lab. I am not saying that it cannot be safely used. just that it is difficult to do, and costs a lot to do it right. Using sodium bifluoride is a good way to etch glass, and it is much safer to work with, but still poisonous and corrosive. I have seen HF burns, they never heal all of the way, thankfully I avoided any, by being careful and not working with it any more than absolutely necessary. And I agree with PirateDocBrown, I have also worked with many horrible chemicals, and would still prefer many of them to HF.

Just did a large bromination today, my tygon tubing is now orange, my oil bubbler is red, and the hood is more corroded than before. My labmate tried to use a plastic syringe with it, and I warned him it does not do well, and sure enough the plastic started softening shortly after he was done, but it as a small scale, and that was the best way to measure it out for him (in a hood, with gloves). But at least the bromine was not quite as nasty as HF.

ave369 - 9-12-2016 at 05:27

I've made bromine. Yes, the smell is a killer, it lingered at my apartment for a long time, and you don't want it to be anywhere near your skin. But HF, I fear to approach that. I have a stock of sodium fluoride in my lab, and it is mostly sitting there idly.

[Edited on 9-12-2016 by ave369]

Dr.Bob - 9-12-2016 at 07:32

There is some fluorine chemistry than can be done without as much risk, but most is pretty nasty. Inorganic fluorides also can be useful, but not commonly used at home, other then in roach killer and toothpaste.