Jor
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caesium carbonate
I have 100 grams of CsCl here, and I want to convert some of this to caesium carbonate, to make other cesium salts, such as the bromide. The problem
is that both are extremely soluble.
One way wich would in theory work is to dissolve cesium chloride and sodium carbonate in water, and extract this solution with ether, followed by
evaporation. However, because the carbonate is so soluble in H2O and I suspect not nearly as soluble in ether, this would require extremely large,
dangerous, expensive volumes of ether to obtain a usable amount of cesium carbonate.
I'm looking for a method in wich no cesium is lost (yield 90% minimum, because it is expensive).
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woelen
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Make caesium permanganate from it. Solubility of CsMnO4 only is around 0.23 gram per 100 ml of water of 20 degrees. Solubility of KMnO4 is well over 6
grams at the same temperature. Just mix stoichiometric amounts of solutions, or even better, use an excess amount of KMnO4 to drive the solubility of
CsMnO4 even lower.
The CsMnO4 then must be strongly heated in order to decompose the permanganate, such that a mix of Cs2O and MnO2 is obtained. The Cs2O then can be
leached from the mix, with insoluble MnO2 left behind.
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entropy51
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Electrolysis of aqueous cesium chloride should yield the hydroxide, which could then be reacted with CO2 to give the carbonate, or directly with HBr
to give cesium bromide.
The hydroxide is said to etch glass.
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not_important
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Sounds like a job for ion exchange resin, trickle CsCl solution through a column of anion exchange resin charged with carbonate/bicarbonate. Make sure
there enough resin that there is a good excess so the lower end of the column never sees chloride.
Another way, perhaps. Evaporate CsCl with HNO3 repeatedly, the chlorine is driven off leaving CsNO3. Evaporate to dryness, ignite to get the oxide,
dissolve in alcohol and treat with CO2 to get Cs2CO3.
Expensive route would be to treat a solution of CsCl with silver oxide, filter and then treat with CO2. Silver carbonate might work to directly give
Cs2CO3, again the AgCl would be filtered off.
hmmm ... a mixed solution of CsCl and "ammonium carbonate", then slowly add alcohol, lots of it. Ammonium chloride is only slightly soluble in EtOH or
i-PROH, no more than a few grams per liter; many caesium salts have fair to good solubilities in in the lower alcohols - Cs2CO3 is around 100 g/l in
EtOH. Thus the ammonium salts precipitate out, a large excess of ammonium carbonate should force the balance in favour of caesium carbonate. Filter
of ammonium salts, evaporate (with recovery of alcohol) and heat to decompose ammonium salts. Repeat to further push the conversion to the carbonate,
finally wash with a small amount of cold alcohol in which CsCl is much more soluble that the carbonate.
Alternatively use a mostly alcohol solution of urea and CsCl, keep hot - perhaps even reflux. The urea hydrolyses, eating up water; the ammonia and
CO2 in water are "ammonium bicarbonate", a mix of ammonium chloride and carbonates should ppt out. Again, use an excess of urea, evaporate the
solution with alcohol recovery, then dissolve in hot water and boil for awhile to decompose any urea and ammonium carbonate.
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blogfast25
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At 50 w% hot NaOH attacks glass, including 'kitchenware' Pyrex glass. Not sure about CsOH...
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DJF90
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It does indeed etch glass. Same is true of LiOH AFIAK. Woelens idea with permanganate sounds good; what sort of temperatures would be required? Do you
have a written procedure for it, or was it your own idea?
[Edited on 10-10-2010 by DJF90]
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not_important
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One more - fume the CsCl with H2SO4 to convert it to the sulfate, boil with a large excess of BaCO3 for some time. Cool & filter, dry,
recrystallise from alcohol preceded by filteration - both barium salts have quite low solubilities in alcohol. Several treatments with BaCO3 before
recrystallising might give higher yields / purer product. Should give good yields, splattering during H2SO4 fuming and loss to mother liquor in
crystallising are the main possibilities of loss of Cs, taking care during the first and standard crystallisation technique of 2nd and 3rd cropping
does the latter.
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woelen
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Quote: Originally posted by DJF90  | It does indeed etch glass. Same is true of LiOH AFIAK. Woelens idea with permanganate sounds good; what sort of temperatures would be required? Do you
have a written procedure for it, or was it your own idea?
[Edited on 10-10-2010 by DJF90] |
The idea with permanganate is my own idea. I know that the solubility if CsMnO4 is very low and that permanganate is decomposed by heat. A well known
demonstration experiment is making oxygen from KMnO4 by heating it in a test tube. At moderate heating, a mix of K2MnO4 and MnO2 is produced, at
stronger heating, K2MnO4 is decomposed as well. When the K2MnO4 is added to neutral water, then it almost immediately decomposes, giving MnO2, O2 and
KOH.
I assume that CsMnO4 will have properties very similar to KMnO4 when it is heated and then that could be exploited to make MnO2 and a solution of
CsOH.
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CsOH does attack glass, but not more, nor less, than any other fully ionized hydroxide. It is the hydroxide which is the active species, so you can
expect a solution of e.g. 1 M CsOH to be as corrosive as a solution of 1 M KOH or NaOH.
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Jor
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Thanks for all you ideas! I think I will go the permanganate way, but the options not_important described also sound attractive, especially heating
the CsCl with HNO3.. i thought of this method myself as well. It is virtually the opposite you do when recovering precious metals (wich I am currently
doing again with Pt and Pd), where you boil with HCl until all nitrate is removed. I might add a little silver nitrate, so I have an indication when
all chloride has been oxidised (dissolving of the AgCl precitipate). I currently don't have time to experiment anymore, did a lot of experimenting
this weekend, but now I will have to wait again for 2 weeks. So I will let you all know!
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phlogiston
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Electrolyse a solution of CsCl using a mercury cathode. An amalgam will form. Take the amalgam and allow it to react with water. Ceasium hydroxide
solution will form, and the mercury is recovered.
-----
"If a rocket goes up, who cares where it comes down, that's not my concern said Wernher von Braun" - Tom Lehrer |
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woelen
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How easy would it be to make Cs2O from CsNO3? I am afraid that this will be VERY hard. Heating it strongly gives CsNO2 (just like the potassium salt
gives KNO2). Before the nitrite decomposes further I expect you will need strong heating, probably so strong that it will become dangerous without a
special metal vessel which can withstand the high temperature and strongly oxidizing material.
On the other hand, permanganate can already be decomposed in a normal test tube. Just try it with some KMnO4. Crunch the material to a fine powder,
put in a test tube and heat fairly strongly, but no red glow is needed. After this, put the material in water. The solution should become pure green
without any purple in it. If you leave that solution standing for a while, then MnO2 precipitates from it and oxygen is evolved. The liquid becomes
alkaline. So, you can try this first without using expensive Cs-salts, first try it with KMnO4.
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not_important
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Can always add some carbon to the nitrate, slowly add the mix to a hot container. You'll want to do either method in a silver plated container
anyway, Cs2O will attack glass when hot. Note that some of the Mn is likely to end up as manganate, I don't recall seeing a colourless leachate of
heat-decompossed KMnO4, it was always greenish or purple if the KMnO4 hadn't completely decomposed.
Why not just boil the CsMnO4 with a lower alcohol, methanol would seem to be ideal? CsMnO4 + CH3OH =[details omitted]=> MnO2 + CsHCO3 + H2O Might
saturate the reaction solution with CO2 JIC, then filter, evaporate, heat to ~100 C to decompose any CsHCO3, recrystallise from alcohol.
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