blogfast25
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Searching for Lithium and Rubidium in Lepidolite
Lepidolite, empirically KLi<sub>2</sub>AlSi<sub>4</sub>O<sub>10</sub>F(OH) (MM = 388.3 g/mol), is a mica type
mineral that often contains rubidium (Rb, presumably through substitution of the K) and sometimes caesium (Cs), besides the valuable lithium (Li).
Lepidolite pieces, slightly over-exposed:
This is an attempt to show the presence of lithium and rubidium (and possibly also caesium) by means of simple spectrometry.
Lepidolite is usually fused with an excess of crushed limestone at 1200 – 1500 C and until most of the limestone has been converted to lime (CaO).
As this is outside my temperature envelope I tried to fuse 1 part crushed Lepidolite with 2 parts of slaked lime (Ca(OH)<sub>2</sub> at high Bunsen heat for 1 hour but on cooling it soon became apparent no reaction had
taken place at all: it takes a much higher temperature to digest this alumino silicate in a solid-solid reaction.
I decided then to resort to alkaline fusion with NaOH, in the knowledge that most of the sodium would be separable because NaCl is poorly soluble in
concentrated HCl.
So to that effect 11.3 g of crushed Lepidolite was mixed with 22.6 NaOH small prills and fused for 20 min in a nickel crucible with lid, on high
Bunsen heat.
It has to be said that this mineral is hard to grind because of its lamellar structure, which causes these lamellae to glide over each other with
minimal friction. With a combination of pounding and grinding action, something was obtained that I deemed sufficiently rich in surface area, although
by no means a powder in the narrow sense of the word.
After fusion, the contents were transferred into a beaker, not without considerable effort: this frit was very hard. Softening up with small aliquots
of hot water and creative use of a chisel did the trick. No unreacted Lepidolite was observed. Grinding the frit also proved hard.
To it was added about 50 ml of HCl 37 % and after simmering this was diluted to about 200 ml. An insoluble, off white residue remained and was
filtered off. At this point I assumed all silica and fluorine (as sodium hexafluoroaluminate) to be in the residue and all Al, Na, K, Li, Rb and Cs to
be in the clear filtrate.
The filtrate was carefully alkalised with NH3 33 w% to pH about 9 and the aluminium precipitated as Al(OH)3:
Note that this causes ammonium chloride to be introduced into the mix of alkali metal chlorides.
The filtrate was then boiled in, in an Erlenmeyer, until crystals started to appear and bumping became intolerable. On cooling the crystals were
filtered off and about 36 ml of clear filtrate was obtained. 72 ml of HCl 37 w% was added and another batch of NaCl dropped out:
It’s possible that these crystals contain also KCl, as it too is insoluble in strong HCl.
These crystals were filtered off on a ceramic filter of medium porosity with vacuum. The filtrate is now supposed to contain all LiCl, all RbCl, all
CsCl, most KCl, some NaCl and the NH<sub>4</sub>Cl.
That is about as far as I got to date.
The plan is now to split the alkali metal chlorides into two groups, according to a scheme which is elaborated here (I have the free, full version on
paper):
http://www.worldcat.org/title/radioactivity-of-the-rubidium-...
(The Radioactivity of the rubidium extracted from the lepidolite and zinnwaldite of Japan, by S. Iimori and J. Yoshimura Lepidolite from Nagatori,
Chikuzen Province, and the lithium content of Japanese mica, by S. Iimori and J. Yoshimura.)
In it, the authors make use of the insolubility of the hexachlorostannates of K and Rb in conc. HCl. Adding
H<sub>2</sub>SnCl<sub>6</sub> to the last filtrate should precipitate NH4, K, Rb (and presumably but not mentioned in that
paper, also Cs) as M<sub>2</sub>SnCl<sub>6</sub>. Filtering then creates a separation between (Na, Li) and (NH4, K, Rb, Cs).
I have in the past independently verified the insolubility of both ammonium and potassium hexachlorostannates in conc. HCl.
For K and Rb the paper lists solubility values of these hexachlorostannates in d = 1.185 HCl at 20 C as 0.0689 (as KCl) g/100 ml for K and 0.0093 (as
RbCl) g/100 ml for Rb. No values for NH4 or Cs are given.
A solution of H<sub>2</sub>SnCl<sub>6</sub> (from HCl, SnCl<sub>2</sub> and
H<sub>2</sub>O<sub>2</sub> has been prepared and will be
allowed to stand overnight, to allow full oxidation of the Sn(II) to Sn(IV).
[Edited on 2-2-2014 by blogfast25]
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elementcollector1
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Interesting! Although, rubidium is present in lepidolite in *extremely* low concentrations, so I'm interested to see your yield.
Elements Collected:52/87
Latest Acquired: Cl
Next in Line: Nd
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blogfast25
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This one isn't really about yield, EC1, it's about detecting it. At best what I'm doing is here is semi-quantitative. Various steps will 'lose' some
of the Li and Rb, other steps will not achieve complete separation. It's not intended as a means to obtain weighable quantities.
Wiki:
"In 1861 Robert Bunsen and Gustav Kirchhoff extracted 150 kg of lepidolite and yielded a few grams of rubidium salts for analysis, and therefore
discovered the new element rubidium."
Acc. the authors of the cited paper, they found about 1 % Rb (as Rb2O) in a sample of their Lepidolite!
Even my goal of finding the main red spectral line of Rb (in the concentrate) with my spectrometer may not be achieved...
[Edited on 2-2-2014 by blogfast25]
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UnintentionalChaos
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You have got to be kidding me. I have been reading into lepidolite processing for a few days after having found some sacrificial flakes while cleaning
my closet out. I have about 40g of pulverized material ready to go right now...
A coffee grinder reduces the soft mica to dust, provided you can break it into smaller flakes first.
I have been looking into processing methods. This CaCl2/NaCl eutectic fusion looks quite doable, even if not optimized to the extent they claim.
http://www.ysxbcn.com/down/upfile/soft/20120806/32-p1753.pdf
This public domain book from 1900 gives some discussion on lepidolite (and other lithium ore) processing starting on page 411:
https://play.google.com/store/books/details?id=dFlBAQAAIAAJ
This is also an interesting skim, while less related. http://www.minsocam.org/ammin/AM18/AM18_454.pdf
[Edited on 2-4-14 by UnintentionalChaos]
Department of Redundancy Department - Now with paperwork!
'In organic synthesis, we call decomposition products "crap", however this is not a IUPAC approved nomenclature.' -Nicodem
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violet sin
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cesium test by use of permanganate might work, if it is present
https://www.google.com/patents/EP0131810B1?cl=en&dq=cesi...
still getting around to that project. but so little time for anything. but if you are starting with chlorides than why not.
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UnintentionalChaos
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Minor update. I feel like a newb when I'm doing inorganic experiments. I don't have crucibles, furnace, temperature control, or even something to
measure high temps. So I got a stainless steel condiment cup (aka: walmart brand disposable crucibles) and initially attempted to heat 20g of
lepidolite "flour" mixed with 12g of finely powdered NaCl and 8g of finely powdered anhydrous CaCl2. I got the metal up to cherry red for quite some
time with a propane torch, but the crucible's contents either remained a loose powder or clumped slightly due to melted salts. Mica is a wonderfully
infuriating insulator. I killed the heat, scraped out the powder, and measured out half of it. I melted an additional 10g of NaCl/CaCl2 mix in the
crucible and slowly fed the original reaction mix into it. It forms a stiff/crumbly paste as you add more and more mica mixture. I eventually got all
of it in and put a clay lid on the crucible. I left the torch on it for 15 minutes more.
The product is light tan low density solid in varying sized lumps that required effort to remove. It is contaminated with oxides from the crucible
though I dont think they will interfere. It has lost the lepidolite's lovely purple tinge.
I ground the product into a powder and am now leaching it with 50ml of distilled water. Theoretically the filtrate should then contain NaCl, CaCl2,
LiCl, and KCl with traces of cesium and rubidium chlorides. Sodium sulfate can ppt the calcium, HCl can remove a lot of the KCl and NaCl, and the
concentrated final solution can be precipitated with carbonate if it indeed worked.
Assuming this method works, obviously a nonreactive crucible would be an improvement. Also, either 4x by mass as much salt mixture needs to be used so
the melt can actually be stirred or the original single mass eq. of salts and mica need to be ball milled together and heated in a proper furnace to
the desired ~880C.
[Edited on 2-4-14 by UnintentionalChaos]
Department of Redundancy Department - Now with paperwork!
'In organic synthesis, we call decomposition products "crap", however this is not a IUPAC approved nomenclature.' -Nicodem
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blogfast25
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@UC:
Wunderbar!
A few points.
Coffee grinder: should have thought of that! But my small, thin lamellae dissolved easily into the molten NaOH.
Crucible: I've never looked back since I bought a nickel one. Indestructable and oblivious to molten alkali or hot conc. H2SO4. Drop it and it bounces
back! Every home lab should have one, mandatory! 
Ca separation: precipitate as carbonate, the sulphate is still slightly soluble.
Do you plan any type of separation of Li, K, Rb and if so, how?
Personally I think 'fusion' (not literally) with CaO would have a lot going for it. This way, you 'block' all Si, Al and F immediately. Then leach
with water for Group I hydroxides. But temperature needed is very high.
Thanks for the links! The minsoscam *.pdf is interesting to me because of the spectrum. I'll check these values against NIST's vast spectral database.
[Edited on 4-2-2014 by blogfast25]
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neptunium
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i suppose Rubidium could be easily identify because of its natural radioactivity as long as a few milligram could be collected...possibly even less!
I easily detect K40 in 15 min from 2lbs of KOH
http://www.sciencemadness.org/talk/files.php?pid=317190&...
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blogfast25
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@neptunium:
Rb-87 is even less radioactive than K-40: half-lives resp. 45 x 10<sup>9</sup> and 1.25 x 10<sup>9</sup> years (Wiki).
You won't see much from a few mg of Rb, if it takes you 15 minutes for 1 kg of KOH!
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neptunium
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true . but it makes up a much bigger percentage than K40...
I was able to pick up Bi214 in the walls of my basement after 5 hours...
http://www.scimad.org/users/neptunium/5_h_snow.jpg
i dont think Rb87 would be a problem if its there at all
[Edited on 5-2-2014 by neptunium]
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Metacelsus
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I don't have much experience with gamma ray spectra, but that graph doesn't look convincingly like 214Bi to me (or if it is, it's swamped
by other stuff). What makes you think there would be significant 214Bi in your basement walls, as opposed to other radionuclides?
[Edited on 5-2-2014 by Cheddite Cheese]
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neptunium
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the detector is a fairly big NaI scintillator without shielding, all the walls arround it are concrete.
with a long enough acquisition, even faintly isotopes can be picked up as long as the energy is high enough (to stand out from the background) the
shielding i am working on should help with the lowest energies (although i also have a x ray detector that perfoms very well untill about 100 Kev)
in the region of the Bi214 peak there isnt much else going on so it is detectable , even though Bi 214 only has a 20 minute half life and is barely
present in concrete and building materials .
http://www.gammaspectrometry.co.uk/examples/200kbgd/200kbgd0...
given a time of acquisition long enough and a proper shield arround the detector i am curious to see if i could pick up Rb87 .
it is a lot less active than K40 true but it represent a much larger percentage of natural Rubidium.
it would be interesting to see...
[Edited on 5-2-2014 by neptunium]
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