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Author: Subject: Uranium Isolation
StevenRS
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[*] posted on 24-5-2008 at 08:55


Uranium actually melts (1132.2 °C) fairly easily. It could be cast under an inert atmosphere without difficulty using a special method were the mold and reservoir are one piece, and both are heated together, never exposing the uranium to the atmosphere.

Cast uranium bullets? That would be very cool.

Simply decomposing the uranium iodide in a tube was to good to be true, just a half-serious idea.

Decomposing the uranium on a tungsten filament hot enough to melt the uranium metal formed seems the way to go. Anyone have the resources to test it with a different metal with similar properties?

This would avoid dealing with pyrophoric powders or fluorine and its compounds.

The electrolysis method sounds pretty good too, it avoids high temperatures, but electrolysis is a slow process, and creating bulk uranium would be difficult.

One more thing, fired clay is resistant to hot halogens, correct?

[Edited on 24-5-2008 by StevenRS]
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[*] posted on 29-5-2008 at 08:40


I am finally back in town, and this is my method for pure uranium metal.

4Al + 3UCl4 --> 3U + 4AlCl3

This would be performed in a crucible, partially sealed from the air. When completed, the crucible would be heated enough to drive off the volatile AlCl3, producing pure uranium.

Possibly, an excess of aluminum could be added to form a flux on top of the uranium if they do not alloy.
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[*] posted on 29-5-2008 at 10:16


I would think the Kroll process would be quite suitable, giving a bit more reasonable end product, MgCl2, instead of that weird AlCl3. MgCl2 is still volatile enough to drive off the metal, and would be an excellent flux. An MgO crucible and inert gas cover would probably be sufficient. Though UCl4 probably has to be led in slowly, as in the Kroll process proper, to control reaction temperature. Maybe something less reactive, but not too much less reactive, would be suitable. Um, let's see Zn, Al, Mg -- dangit, there aren't many common metals within that narrow range of reduction potentials!

Al and U probably form numerous intermetallics, a shame I don't have the phase diagram. For example, the Al-La system contains an intermetallic with melting point substantially higher than either metal -- maybe not too big a stretch to call that an aluminide, as if. If uranium is more white-metal-like, the Al-Pb system is immiscible with only minor solubility, but I feel that's unlikely.

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[*] posted on 29-5-2008 at 16:01


Quote:

This would be performed in a crucible, partially sealed from the air. When completed, the crucible would be heated enough to drive off the volatile AlCl3, producing pure uranium.

Possibly, an excess of aluminum could be added to form a flux on top of the uranium if they do not alloy.


I suspect you'll find that anything less than a good seal will reduce if not thwart the effectiveness of this approach. Uranium loves oxygen

Quote:
One more thing, fired clay is resistant to hot halogens, correct?

Not entirely, depends on the clay. More important would be the porosity of the ceramic; much of the non-glazed commercial ceramics are porous enough that they'll bubble when immersed in water and absorb water as well.


Segregation in uranium-aluminum alloys
http://www.ornl.gov/info/reports/1958/3445603505721.pdf


THE ALLOY SYSTEMS URANIUM-ALUMINUM AND URANIUM-IRON
http://www.osti.gov/bridge/servlets/purl/4449905-4O7Sdg/4449...
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[*] posted on 31-5-2008 at 05:12


This patent relies on the reduction of UCl4 with Mg:

Quote:
c. Reduction of Uranium Tetrachloride to Metallic Uranium

The uranium tetrachloride powder formed and collected in the chlorination operation is now fed to a reduction operation where the uranium tetrachloride will be reduced to form metallic uranium. The uranium tetrachloride is reduced by contacting it with a metal which is a greater reducing agent than uranium in the electromotive-force series, whereby the uranium tetrachloride will reduce to metallic uranium while the other metal is oxidized to form the corresponding chloride of the metal.

A preferred group of reducing metals which may be useful in carrying out this step of the process is either lithium or the alkaline earth metals such as calcium, magnesium, barium, and strontium. Preferably the reducing metal is either calcium or magnesium metal, and most preferably the reducing metal is magnesium. The following equation., using magnesium as the reducing metal by way of illustration, and not of limitation, shows the uranium reduction reaction.


No mention of Al though.

I can't find the heat of formation of UCl<sub>4</sub>. For AlCl<sub>3</sub> it's - 706 kJ/mol, for MgCl<sub>2</sub> it's - 641 kJ/mol, for KCl - 437 kJ/mol.

If the heat of formation of UCl<sub>4</sub> is ΔH, then the reaction enthalpies are:

UCl<sub>4</sub> + 4/3 Al ---> U + 4/3 AlCl<sub>3</sub>

Reaction enthalpy = - ΔH - 941 (kJ/mol)


UCl<sub>4</sub> + 2 Mg ---> U + 2 MgCl<sub>2</sub>

Reaction enthalpy = - ΔH - 1282 (kJ/mol)


UCl<sub>4</sub>. + 4 K ---> U + 4 KCl

Reaction enthalpy = - ΔH - 1748 (kJ/mol)

So, Al would be the least exothermic.

It doesn't sound implausible that the heat of formation of UCl4 would be somewhere in the 900 kJ/mol range, in which case higher temperature and removal of the AlCl3 would be needed to make the Al reduction proceed. For TiCl4, the heat of formation is - 815 kJ/mol.

[Edited on 31-5-2008 by blogfast25]

[Edited on 31-5-2008 by blogfast25]
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StevenRS
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[*] posted on 14-6-2008 at 12:42


I attempted the reduction of UCl4 with magnesium, and it was a success and a failure at the same time. It reacted quite quickly, but when the reduction was over, the uranium caught fire. (I think.) I expected this a little. All I need to do is stop the uranium from caching fire, and then heat it to drive of most of the magnesium chloride. I have a propane furnace, so heat is not a problem for me at all.
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[*] posted on 17-6-2008 at 09:32


Quote:
Originally posted by StevenRS
It reacted quite quickly, but when the reduction was over, the uranium caught fire. (I think.) I expected this a little.


If someone here has the heat of formation (@ 298 K) of UCl<sub>4</sub>, then it would be possible to estimate the end-temperature of the reaction in adiabatic conditions. With a boiling point of 1,412 C (for MgCl<sub>2</sub>;) the reduction reaction may well be energetic enough to cause the MgCl2 to sublimate off, leaving the unprotected, very hot metal exposed to air. This could explain what happened in your case. In many reductions with Al or Mg, unless the slag sufficiently protects the newly formed metal from the air, inert atmosphere will be necessary to obtain the clean, unoxidised product.
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[*] posted on 18-6-2008 at 02:44


Quote:
Originally posted by MagicJigPipe
I've been reading up on the separation of U isotopes. It just doesn't seem like it would be that difficult for a nation with a decent amount of U ore, modern industrial capacity and some sort of scientific knowledge base.

What am I missing here? What is it exactly that makes extraction of U235 from U ore so difficult for a decent sized nation (other than the hazards of working with fluorine if the gas centrifuge method is used)?


This is the one exception were I think its OK for one to just talk science without the slightest intention or expertise in actually doing it.

Isotopes can not be separated chemically, so the only method must be based on the mass difference. Gas diffusion separation uses the 0.8% mass differece [U(238)F6]/[U(235)F6]. Diffusion of a gas is related to the speed of its particles. I think many people may remember the first year high school experiment of mixing HCl with NH3, the latter move faster on average and so the NH4Cl fog forms predominantly in the HCl container. Thus in a 'single-stage' diffusion 0.4% more U235 will diffuse than its proportion in the original mixture. Repeat this n times using (1.004)^n and you can get the U235 fraction close to 1. Imperfections in the centrifuges will mean that the apparatus loses separation power as you get close to that 1. For a chain reaction you need enrichment to only about 5%.

There is no reason why any, even small, nation cant do this. To whit Israel with 3mln people. Most just dont want to.

As far as ore goes, you need 17kg U235 for one atom bomb thats a 10cm cube, or about 2.3ton natural uranium - thats a 45cm cube, which equates to 2.7ton of uranium ore concentrate U3O8. The average U concentration is 0.3% in Australian ore - so one atomic bomb = 690ton uranium ore - I need to order about 35 truck loads. Actually the centrifuge process is only about 70% efficient, while U smelting extracts max 85% U from Australian ore - so make that 1200ton, or 60 truck loads - not that much really - if only I had settled in Olympic Dam before 1975.

It is obvious from the above that an atom bomb is a huge waste of uranium - 99.5% is wasted (explains why depleted U costs 5$/kg). If you enrich your uranium to only 5%, and run it in a beeder, youll extract the energy from the U235, while the neutrons from the latter - 2.4 on average - will convert 2.4 its amount to Pu - another useful element. This way only 98% of natural U is wasted - but still too much. I think an H-bomb (actually its a lithium deuteride an isotope of LiH bomb) is a much 'greener' solution. It wastes only 45% natural uranium - U238 also fissions (I presume mostly thru Pu), it just doesnt release enough neutrons for a chain reaction, but in the neutron rich environment of an H-bomb, it reacts yielding about 50% of total energy.

[Edited on 18-6-2008 by len1]
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[*] posted on 18-6-2008 at 10:04


The following patent seems to suggest that the heat of the reduction reaction of UCl<sub>4</sub> with Mg is not enough to obtain the Uranium metal in liquid form and goes on to discuss the possibility of obtaining a lower meting alloy with Iron:

Process for continuous production of metallic uranium and uranium alloys:

Quote:
The uranium tetrachloride powder formed and collected in the chlorination
operation is now fed to a reduction operation where the uranium
tetrachloride will be reduced to form metallic uranium. The uranium
tetrachloride is reduced by contacting it with a metal which is a greater
reducing agent than uranium in the electromotive-force series, whereby the
uranium tetrachloride will reduce to metallic uranium while the other
metal is oxidized to form the corresponding chloride of the metal.


A preferred group of reducing metals which may be useful in carrying out
this step of the process is either lithium or the alkaline earth metals
such as calcium, magnesium, barium, and strontium. Preferably the reducing
metal is either calcium or magnesium metal, and most preferably the
reducing metal is magnesium. The following equation., using magnesium as
the reducing metal by way of illustration, and not of limitation, shows
the uranium reduction reaction.


UCl4 +2Mg ---> U+2MgCl2 (4)


While the above reaction is capable of forming metallic uranium, without
further additives, the resulting metallic uranium has a melting point of
about 1132° C. This necessitates carrying out the reaction at this
temperature or higher in order to maintain the uranium in liquid form in
the reactor to facilitate its removal when the reaction is carried out on
a continuous basis.


It would, therefore, be preferable to add to the reaction another metal
which is capable of alloying with the uranium to form an alloy or alloys
with lower melting temperatures than pure uranium. Typically, such metals
are those which form eutectic systems with uranium. These metals should
not interfere with the reduction reaction being carried out. A preferred
metal additive for this purpose is iron which, for example, will alloy
with uranium at a mole ratio of about 33 mole % iron, 67 mole % uranium
to form a low melting eutectic alloy having a melting point of about
725° C.


Other metals which could be used instead of iron, i.e., metals which can
form an alloy with a melting point lower than that of pure uranium
without, however, interfering with the uranium reduction reaction,
include: (a) one or more metals which form eutectic alloy systems with
uranium in which uranium is the major alloying constituent (i.e., in the
order of 60 mole % or higher), such as chromium, manganese, cobalt,
nickel, and the platinum metals ruthenium, rhodium, palladium, osmium,
iridium, and platinum; and (b) one or more metals which form eutectic
alloy systems with uranium in which uranium is the minor alloying
constituent (i.e., in the order of at least about 1 mole %, but less than
about 15 mole %) such as aluminum, gold, silver, copper, germanium, and
zinc.


And this here purchasable paper probably contains the value of UCl<sub>4</sub>'s heat of formation...
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[*] posted on 18-6-2008 at 10:30


Quote:
Originally posted by blogfast25
And this here purchasable paper probably contains the value of UCl<sub>4</sub>'s heat of formation...

Though articles are otherwise requested in References, here it is for the those interested:

The standard molar enthalpy of formation of UNCl
M. Akabori, F. Kobayashi, H. Hayashi, T. Ogawa, M. E. Huntelaar, A. S. Booij and P. van Vlaanderen
The Journal of Chemical Thermodynamics, 34 (2002) 1461-1466.

Attachment: The standard molar enthalpy of formation of UNCl.pdf (90kB)
This file has been downloaded 1334 times

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[*] posted on 18-6-2008 at 12:05


Great!

From this paper the standard molar enthalpy of reaction at 298 K for U (s) + 2 Cl<sub>2</sub> (g) ---> UCl<sub>4</sub> (s) to be ΔH = - 1,018 kJ (per mol of UCl<sub>4</sub>;) (see page 5, Table 3) can be gleaned.

For UCl<sub>4</sub> (s) + 2 Mg (s) ---> U (s) + 2 MgCl<sub>2</sub> (s) we then obtain ΔH = - 264 kJ (per mol of UCl<sub>4</sub>;). That's only barely exothermic and almost certainly insufficient to melt both the U and the MgCl<sub>2</sub>. To be confirmed/infirmed tomorrow...
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[*] posted on 18-6-2008 at 17:36


While checking on the Fray-Farthing-Chen-Cambridge process for another thread, I noticed that UO2 can be reduced by FFC means. This results in lightly sintered powdered uranium in frozen CaCl2 electrolyte, so the workup would need to be done in a inert atmosphere followed by melting and casting.


There's a reasonable description of the standard Mg-UF4 process here
http://www.barc.gov.in/webpages/letter/2000/200009-04.pdf

and some early 20th century experience here

http://books.google.com/books?id=lC4OAAAAYAAJ&pg=RA3-PA1...

which includes the comment
Quote:
An interesting feature developed in these experiments was the ease
with which metallic uranium oxidizes. In working with a charge which
produced uranium, or metal and carbide, if the button of sponge metal
was removed from the furnace while still red hot, and exposed to the air,
it immediately oxidized to black uranium oxide, a 25-lb. button being
converted completely to oxide in less than 5 minutes.
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[*] posted on 19-6-2008 at 09:03


Very interesting description of the UF<sub>4</sub>/Mg reduction process indeed! But fluorination of U is probably outside the capability envelope of most backyard scientists and the UCl<sub>4</sub>-route looks more promising from that perspective, so it's a case of finding the most suitable reductant. Ideally (for backyard science), the RT UCl<sub>4</sub>/reductant mixture would be lit with an ignition pill and the temperature developed during reduction would be high enough to melt both the metal and the slag, leading to gravitational separation of the (in this case very heavy) metal from the molten chloride/U metal mix.

Al itself can be excluded as UCl<sub>4</sub> + 4/3 Al ---> U + 4/3 AlCl<sub>3</sub> is not exothermic (ΔH = + 77 kJ at 298 K).

The main reductants to be considered are Mg and K, IMHO (at least at first glance).

The enthalpy needed to heat 1 mol of U from 298 K to its MP (1,405 K) is approximately 39 kJ (including heat of fusion).

The enthalpy needed to heat 2 moles of MgCl<sub>2</sub> from 298 K to 1,405 K (including heat of fusion at MP = 987 K) is approximately 227 kJ.and for UCl<sub>4</sub> + 2 Mg ---> U + 2 MgCl<sub>2</sub> the heat of reaction (at 298 K) is about - 266 kJ (per mol of U). So basically (by sheer coincidence) 39 kJ + 227 kJ = 266 kJ. The Mg reduction, started from 298 K and carried out in adiabatic conditions would probably just about reach the MP of uranium. In reality we're cutting it fine and heat losses will probably lead to slightly lower end-temperature and thus poor metal/slag separation.

The enthalpy needed to heat 4 moles of KCl from 298 K to 1,405 K (including heat of fusion at MP = 1,049 K) is approximately 364 kJ.and for UCl<sub>4</sub> + 4 K ---> U + 4 KCl the heat of reaction (at 298 K) is - 730 kJ. Since as 730 kJ > 39 kJ + 364 kJ (730 kJ > 403 kJ), the reduction with K has kilojoules to spare and should heat to well past the MP of U. Perhaps this partly explains why in1841, Eugène-Melchior Péligot, who was Professor of Analytical Chemistry at the Conservatoire National des Arts et Métiers (Central School of Arts and Manufactures) in Paris, isolated the first sample of uranium metal by heating uranium tetrachloride with potassium.

Interestingly, the results with Li are very similar to those with K: heat of reaction (at 298 K) is about - 614 kJ, the enthalpy to heat 4 moles of LiCl from 298 to 1,405 K (including heat of fusion at MP = 881 K) is about 334 kJ, so 614 kJ > 39 kJ + 334 kJ (614 kJ > 373 kJ). This too should run to well past the MP of U, at least in adiabatic conditions.

Li being easier to handle than K, it would be my own choice of reductant, if I possessed some UCl<sub>4</sub>. :(

Li is of course more difficult to obtain/produce in fine form than Mg and a mixture (layered perhaps?) of UCl<sub>4</sub> and coarse Li may have to be furnace heated in order to trigger the reduction reaction... But both powdered and pelletised lithium are commercially available (but maybe not to backyarders...)

[Edited on 19-6-2008 by blogfast25]

[Edited on 19-6-2008 by blogfast25]

[Edited on 20-6-2008 by blogfast25]
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[*] posted on 28-12-2008 at 13:24


Just remembered this thread and the use for lithium.

I wonder if lithium for deOxing copper alloys would be sufficient. I suppose one could easily cut one of the copper capsules in half with a band saw and melt out the Li under argon.


This company sells it.
http://www.milward.com/index.htm

a description of what it's used for in the casting industry:
http://backyardmetalcasting.com/forums/viewtopic.php?t=927&a...

[Edited on 28-12-2008 by Fleaker]




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