Jor
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Pure V from 90% V metal
I can currently buy an vanadium/aluminium alloy (90% V), for a very good price. Pure vanadium is very expensive.
So I was wondering, if simple heating in NaOH-solution will dissolve all the aluminium leaving V-powder?
Or will, the V powder be pyrophoric, because of the large surface area, just as in the case of raney nickel, when raney alloy is put in NaOH-solution?
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JohnWW
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V is amphoteric in practically all its common oxidation states, so the V would dissolve in highly concentrated NaOH as well as the Al, as well as in
concentrated strong mineral acids; but probably not in any dilute alkalis or non-oxidizing (i.e. other than nitric) acids. A separation procedure, at
least on a fairly large scale, would probably depend in some way on vanadate(V) precipitating out as hydrous V2O5 at a substantially different pH
range from aluminate(III) as hydrous Al2O3, after getting it into alkaline solution. A similar procedure is used in refining alumina from raw bauxite,
e.g. at Gladstone, Queensland, to separate out Fe2O3 (the chief impurity), Ga2O3 (valuable for use in semiconductors, present at about 50 ppm), and
SiO2. However, I have no data on the pH ranges required for such a V-Al separation by precipitation. Another possibility could be some sort of
ion-exchange or column-chromatographic separation from a strongly acid solution (sufficient to practically prevent hydrolysis) of salts of V(III) and
Al(III).
Edit: I have come up with another idea: being a transition metal with plenty of spaces in empty or only half-filled 3d orbitals, V metal should be
capable of forming a volatile V(0) carbonyl by reaction with CO, if necessary under pressure, unlike Al, although probably not as readily as the
less-electropositive transition metals like Ni, Co, Fe. The carbonyl could be distilled off, and then the CO removed. However, this would be feasible
only on an industrial scale, with a source of CO and means for safely handling it.
[Edited on 13-9-09 by JohnWW]
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not_important
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You are not going to separate them as metals using wet methods. To keep the vanadium as metal I think you'd have to use either distilling the Al off
under high vacuum, or electrorefining with molten salt electrolyte.
You might be able to selectively oxidise the Al in a controlled atmosphere at high temperature.
Wet methods to pure vanadium compounds is easier.
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woelen
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There is a reason why pure V-metal is so increadibly expensive (at least one euro gram, probably more expensive). When vanadium is reduced by e.g.
aluminium, iron or carbon, then it forms non-stoichiometric compounds, which are very hard to decompose. Apparently there is no electrolytical method
for purification of vanadium, as opposed to chromium, nickel, copper or iron.
Pure vanadium compounds usually are made from V2O5, which then is reduced. When aluminium is used as reductor, then there always is some aluminium in
the final product, which is not easily removed. You can make pure V2O5 from the metal, but then you are just at the start again. As soon as that V2O5
is reduced with a suitable reductor, then you end up with metal in which some of the reductor is present as well. So, vanadium mixed in with some
other metal (e.g. 80% V, 20% Fe) or in Jor's case 90% V, 10% Al is not expensive at all.
The 90/10 V/Al alloy, however, is quite interesting already on its own. It allows doing interesting and colorful vanadium chemistry in which the
aluminium ions do not have a disturbing effect.
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unionised
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Vanadium might be amphoteric in most of its oxidation states but I don't think zero is one of them. According to Wiki (and a randomly chosen chemistry
textbook) "Vanadium is a soft, ductile, silver-grey metal. It has good resistance to corrosion and it is stable against alkalis, sulfuric and
hydrochloric acids."
The bulk metal is not reactive to alkalies so the idea of "washing" the Al out of it might work a bit. The fact that 90% of the metal won't be
attacked and so will get in the way might be more of a problem.
The raney alloys have a lot more Al in them than 10%.
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