Sciencemadness Discussion Board

fluorosilicic acid?

Skyjumper - 8-3-2010 at 11:43

I have a bottle of fluorosilicic acid (Teflon of course) The bottle is in real poor shape, so I want to get rid of it, or at least make into something better.

Im considering reacting it with an excess of NaOH, via these 2 reactions:

H2SiF6 + 2 NaOH → Na2SiF6 + 2 H2O

Then
Na2SiF6 + 4 NaOH → 6 NaF + SiO2 + 2 H2O

I would then filter off the sand (keeping it, that's some real pure, fine sand)

Then I would react the NaF with calcium hydroxide, yielding Calcium Fluoride, which can be bottled and used for something else later.

Actually, after reviewing this I could just neutralize the acid with an excess of lime water couldn't



I don't see any real use for the acid, and at worst I could always make some HF from the CaF

12AX7 - 8-3-2010 at 12:08

I expect you'll get silica gel... fine sand indeed. :D Depends on the Kf of SiF6 though, it may be too stable to break up, you might need H2SO4 instead.

Needless to say, anything which makes HF (or the similar process, with Fe(CN)6, which makes HCN) is an unwise move.

Tim

Skyjumper - 8-3-2010 at 14:20

Quote: Originally posted by 12AX7  
I expect you'll get silica gel... fine sand indeed. :D Depends on the Kf of SiF6 though, it may be too stable to break up, you might need H2SO4 instead.

Needless to say, anything which makes HF (or the similar process, with Fe(CN)6, which makes HCN) is an unwise move.

Tim


I'm not out to make HF, just a thought on uses of Calcium Fluoride. The acid itself (fluorisilicic acid) evaps to form HF, and having that sit in my acid cabinet is a little concerning... especially in a 30 year old bottle (at least)

Jor - 8-3-2010 at 14:41

Do NOT make cacium fluoride. This is an insoluble useless material. At least make NaF (not very soluble) or better sodium hexafluorosilicate.

HF is not nearly as poisonous as HCN. Yes it may kill you if you splash 5-10mL of the concentrated solution on you but that's still 2,5-5g HF (5-10g NaF is also fatal), but if you spill some liquid HCN or HCN solution on you you may need only less than a mL (some will boil away though).
LC50 for HF is 1276 ppm/1H accoring to JTBaker MSDS, chlorine is 4 times more toxic.
So working with HF as a liquid is an extreme hazard, gaseous HF not more so than chlorine.

Skyjumper - 8-3-2010 at 14:47

Either way, at least I could capture the calcium fluoride, instead of flushing it.

DJF90 - 8-3-2010 at 15:29

HF and Cl2 are incomparable Jor. Hydrogen fluoride may be less toxic than the latter, but its alot more difficult to work with. Consider the boiling point of HF and you'll see part of the problem. Liquid HF is extreme, as are aqueous solutions of it, but they are handle alot easier than gaseous HF.

Jor - 8-3-2010 at 15:59

No I don't see the problem. I stated that liquid HF and solution are an extreme hazard, but I don't see why gaseous HF is more dangerous than Cl2? Handling issues? Other than that it attacks glass, I don't see a difference. Another source states 500ppm/1H for mice, but still about 1,5 times more than chlorine.

Skyjumper - 8-3-2010 at 17:32

*shrugs* I suppose that I will just neutralize the acid and dump it down the drain. That sand will be greatly useful around the lab, such a fine grain.

not_important - 9-3-2010 at 01:13

Don't take it past the NaF stage. After filtering of the SiO2, precipitate the NaF by adding alcohol, wash it with more alcohol then acetone, dry, and store in a HDPE bottle. CaF2 is not worth bothering with, getting the fluorine back into useful form is difficult and generally involves distilling HF away from the reaction mix.

The SiO2 will be contaminated with fluoride and sodium, and will require good washing. Use fairly dilute alkali, mix well, and stir for some time after finishing addition; there's a tendency for pockets of the acid or its sodium salt to get trapped in the hydrated silica.

Jor - 9-3-2010 at 01:13

Well I think that's quite wasteful. Who knows what interesting properties NaSiF6 has, and otherwise NaF is quite useful, and is not that easy to buy.

Skyjumper - 9-3-2010 at 12:14

I like the idea of precipitating out the NaF, never woulda thought of it. Im going to try this tomorrow, and the NaSiF6 is useless (I'm not planning on fluoridating water)

JohnWW - 9-3-2010 at 13:44

As well as for fluoridating water in naturally F-deficient areas, NaF is also used as a poison for rats and other vertebrate pests, mixed with an attractant and flour or jam, although it is not as effective as, for example, warfarin or CH2FCOONa or KCN .

Panache - 9-3-2010 at 15:31

Or aluminium phosphide aka fumitoxin, (wonder who pens those names) componded together with ammonia forming salts to minimise spontaneous combustion of the tasty bite size pellets. I remember when working in pet food how difficult it was making some vitamin additives palletable, drugs even more difficult, i can't imagine how one would go about designing a flavour system to disguise a poison, let alone one that was shelf stable, didn't interact with the toxin and was Halal and Kosher.
I understand your reluctance for anything like the flurosilliicc acid (say the name of this acid to a child and they want play with some, because it's silly!!) hanging around in a suspect bottle, if you live in melbourne i would gladly take it off your hands, likewise if you're going to destroy it may as well take it all the way to calcium salt, you can then grow a nice big crystal and it can sit benignly on a shelf on a bed of the finest $1000/kg sand.
Jor if LD50's where the only data one required to assess the safety of a substance, my roof would not cost $15,000 to remove and Port Pirie and Minimata Bay would still be considered idyllic seaside resorts. I'd happily work with CL2 gas or liquid, there's no residual if you don't die other than nausea for several hours, this is shown for WWI veteran data on a sample of over 1500 veterans (they kept stats on them until their death).
I understand your typically rationale sensibility and emotion and experience removed one could come to your sensibility. It's just that what you suggest is insane that bothers me, lol, lets not talk about splashing HF or HCN on ourselves.

blogfast25 - 12-3-2010 at 13:27

Seems to me the solution to your 'problem' [cough!] is to transfer the hexafluorosilicic acid into a new container. Teflon or thick PE should do.

Wasting it to CaF2 would be ridiculous and NaF you can buy by the bucket.

H2SiF6 would be interesting to study various salts derived from it.

And it's a bloody expensive way to make some fine sand (LOL).

[Edited on 12-3-2010 by blogfast25]

Skyjumper - 12-3-2010 at 14:20

Im considering making a couple of the salts, it interests me, there doesn't seem to be much published about the substance. Would a Nalgene branded bottle (not a drinking one, a legitimate lab reagent bottle) work? The properties of the ammonium salt, and perhaps some organic reactions (very) briefly spoken of in wiki.

chemrox - 12-3-2010 at 18:05

There are numerous containers made for F containing acids. If you want to go cheap, how about a wax coating? I haven't looked up your acid but HF has been contained this way. A poly coated glass bottle could be dipped in hot wax and inverted or better yet rotated while inverted. Linear polypropylene? What about using "tool dip?"

http://www.solvaychemicals.us/static/wma/pdf/1/1/0/0/4/HFS-T...

The above page indicates manufacture in "rubber lined containers." Are rubber lined bottles cheaper than Teflon containers? I have one 2L Teflon bottle that was given to me by a member. I'm using it to store Br2.

not_important - 12-3-2010 at 18:33

Mineral wax is long chain hydrocarbons, as is PE and PP; all are resistant to aqueous HF. PE and PP have the advantage thay they are flexible and will not crack or peel off as wax will. LDPE, HDPE, and PP all are rated 'excellent' at resisting 48% HF at room temperature, HDP/E and PP have the same rating at ~50-60 degrees C.

Rubber lined and gutta percha were used for containing aqueous HF before the development of the polyolefin plastics.

Panache - 16-3-2010 at 16:49

Quote: Originally posted by chemrox  


Are rubber lined bottles cheaper than Teflon containers? I have one 2L Teflon bottle that was given to me by a member. I'm using it to store Br2.


Hows that working, how much Br2 is stored in it, is the thread on the closure very fine or course, what temperature is it you stored at. I had previously tried schott bottles using a teflon lid liner (about (i'm guessing) .2mm thick) and the Br2 soon (~month) was decomposing the PP lid, ie the liner wasn't much chop. I now store the Br2 in an ordinary schott bottle with an ordinary PP lid, at -85C, not much happens.

Newton2.0 - 12-12-2021 at 07:09

Lots of variability for storage containers and all sorts of lids. My Sat. Br2/H2O lost a a lof color...possibly die to outgassivmng or degrading the plastics involved. I have so little use for Br2/H2O that I wonder why I bother. Disinfectant maybe?