testimento
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Extraction of natural occuring minerals (fluorine, mercury)
Due to the authoritarian nature of my country, fluoric compounds are difficult to obtain, so I was thinking of natural source extraction.
My primary interest lies on fluoride and mercury. Fluoride elements occur there and here, and I've seen several cryolite and fluorite stones rolling
around the ground and I'm going to have look around.
Mercury, on the other hand, is not that common for me. I've gotta look around and prepare for unsuccessful journey. This one interests me even more,
since cryolite is MAYBE obtainable for me in worst cases, but mercury is total ban-off and I'm desperately looking a source for it. Even smaller
amounts would suffice, but my goal is to find at least a liter or two(10-30kg) for proper chlor-alkali cell.
How to extract the fluorine? If you mix cryolite with NaOH, will you get hydrogen fluoride gas upon heating? Cryolite formula is Na3AlF6, so as far as
I figure it, why not?
How about other minerals, what comes in your mind what otherways hard-to-obtain items could be collected by this method? It's laborous to go turning
stones to the beach, but I bet there are more stupid hobbies than this.. 
[Edited on 15-7-2013 by testimento]
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bfesser
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Quote: Originally posted by testimento  | | If you mix cryolite with NaOH, will you get hydrogen fluoride gas upon heating? Cryolite formula is Na3AlF6, so as far as I figure it, why not?
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No. Where do you think the H<sup>+</sup> would come from? Write out the reaction
equation—it doesn't make sense.
<strong>Na<sub>3</sub>AlF<sub>6</sub> + NaOH <img src="../scipics/user:bfesser/post_pics/no_rxn.png" align="top"
/> HF + ? </strong>
<em>Perhaps,</em> with <em>insanely high</em> temperature <a href="http://en.wikipedia.org/wiki/Cryolite"
target="_blank">cryolite</a> <img src="../scipics/_wiki.png" /> and hydroxide <em>could</em> yield HF, but there's an
easier way.
<img src="../scipics/_warn.png" /> <em>Extremely Dangerous: Hydrogen fluoride can be prepared by reacting powdered <a
href="http://en.wikipedia.org/wiki/Fluorite#Source_of_fluorine_and_fluoride" target="_blank">fluorite</a> <img src="../scipics/_wiki.png"
/> (CaF<sub>2</sub> with a strong mineral acid, such as
H<sub>2</sub>SO<sub>4</sub>.</em> <img src="../scipics/_warn.png" />
<strong>CaF<sub>2</sub>(s) + H<sub>2</sub>SO<sub>4</sub> → CaSO<sub>4</sub>(s) + 2
HF(g)</strong>
[Edited on 7/16/13 by bfesser]
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testimento
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Oh, my bad, of course you will need acid. Maybe HCl could work too. But anyways, cryolite seems to be the way to go, it can be used to produce HF as
well, and it's weight consists of fluorine more than 50%. 
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testimento
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316 steel is compatible with DRY HF gas, but is corroded at a high rate by a wet one, because it forms a passive layer on the surface of the metal,
which moisture would flush away and corrode the metal.
If I use concentrated, 95-99% H2SO4 with dried mineral at 210C at which the HF is released, this would produce quite dry HF gas as far as I see?
Although, dry HF should be compatible even with glass.. So why not use glass apparatus and HDPE tubing to inject it into water. 
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woelen
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Even tiny traces of water will make the HF very reactive. Water also is formed in the reaction with glass:
SiO2 + 4HF <----> SiF4 + 2H2O
So, only meticulously dried HF when kept in contact with extremely well dried glass does not attack glass. As soon as some attack occured you're lost,
due to the water formed in the reaction. Even when glass is kept in an oven for several days at well over 100 C still some water may be present (bound
to SiO2 or SiO3(2-) as hydroxyl groups). Only well-equipped laboratories can reach conditions like that.
So, in ANY practical setup consider HF as corrosive, eating away glass.
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testimento
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Hmm, something like this I was expecting for. Well, then I'd need to use monel, nickel or 316. A slight corrosion won't matter, I can easily weld a
new reactor if one gets eaten away as happened with my thermite experiments.
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papaya
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Or copper
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gsd
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You can use simple plain MS (Mild Steel). TTBOMK industrial HF handling equipments are made up of MS. Sure, it will get corroded after some use. But
then throw it off and use another one.
gsd
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testimento
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What would be the balanced reaction on Na3AlF6 on H2SO4 to yield HF?
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bfesser
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2 Na<sub>3</sub>AlF<sub>6</sub> + 6 H<sub>2</sub>SO<sub>4</sub> → 3
Na<sub>2</sub>SO<sub>4</sub> + Al<sub>2</sub>(SO<sub>4</sub><sub>3</sub> + 12 HF
[In reality, I think it would yield NaAl(SO<sub>4</sub><sub>2</sub>.]
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testimento
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Hmm, I think it should be determined carefully because that would imply a huge savings on sulfuric acid.
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bfesser
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You could try balancing the equation yourself. I only humored your spoon-feeding request, the first time, out of boredom. Also, I don't see how it
would affect the quantity of sulfuric acid necessary.
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