Skyjumper
Hazard to Self
Posts: 93
Registered: 1-3-2010
Location: Assachusetts
Member Is Offline
Mood: Refluxing
|
|
fluorosilicic acid?
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
Post Harlot
Posts: 4803
Registered: 8-3-2005
Location: oscillating
Member Is Offline
Mood: informative
|
|
I expect you'll get silica gel... fine sand indeed.  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
Hazard to Self
Posts: 93
Registered: 1-3-2010
Location: Assachusetts
Member Is Offline
Mood: Refluxing
|
|
Quote: Originally posted by 12AX7  | I expect you'll get silica gel... fine sand indeed. 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
National Hazard
Posts: 950
Registered: 21-11-2007
Member Is Offline
Mood: No Mood
|
|
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
Hazard to Self
Posts: 93
Registered: 1-3-2010
Location: Assachusetts
Member Is Offline
Mood: Refluxing
|
|
Either way, at least I could capture the calcium fluoride, instead of flushing it.
|
|
|
DJF90
International Hazard
Posts: 2266
Registered: 15-12-2007
Location: At the bench
Member Is Offline
Mood: No Mood
|
|
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
National Hazard
Posts: 950
Registered: 21-11-2007
Member Is Offline
Mood: No Mood
|
|
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
Hazard to Self
Posts: 93
Registered: 1-3-2010
Location: Assachusetts
Member Is Offline
Mood: Refluxing
|
|
*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
International Hazard
Posts: 3873
Registered: 21-7-2006
Member Is Offline
Mood: No Mood
|
|
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
National Hazard
Posts: 950
Registered: 21-11-2007
Member Is Offline
Mood: No Mood
|
|
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
Hazard to Self
Posts: 93
Registered: 1-3-2010
Location: Assachusetts
Member Is Offline
Mood: Refluxing
|
|
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
International Hazard
Posts: 2849
Registered: 27-7-2004
Location: New Zealand
Member Is Offline
Mood: No Mood
|
|
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
International Hazard
Posts: 1290
Registered: 18-10-2007
Member Is Offline
Mood: Instead of being my deliverance, she had a resemblance to a Kat named Frankenstein
|
|
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
International Hazard
Posts: 10562
Registered: 3-2-2008
Location: Neverland
Member Is Offline
Mood: No Mood
|
|
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
Hazard to Self
Posts: 93
Registered: 1-3-2010
Location: Assachusetts
Member Is Offline
Mood: Refluxing
|
|
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
International Hazard
Posts: 2961
Registered: 18-1-2007
Location: UTM
Member Is Offline
Mood: LaGrangian
|
|
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.
"When you let the dumbasses vote you end up with populism followed by autocracy and getting back is a bitch." Plato (sort of)
|
|
|
not_important
International Hazard
Posts: 3873
Registered: 21-7-2006
Member Is Offline
Mood: No Mood
|
|
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
International Hazard
Posts: 1290
Registered: 18-10-2007
Member Is Offline
Mood: Instead of being my deliverance, she had a resemblance to a Kat named Frankenstein
|
|
| 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
Hazard to Self
Posts: 63
Registered: 12-8-2019
Member Is Offline
|
|
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?
|
|
|
![[*]](images/xpblue/default_icon.gif){kind=icon}
