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Mixell
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[*] posted on 10-11-2012 at 10:41
Vanadium Colloid


I've isolated some vanadium from an aluminium-vanadium alloy (15%-85% by mass).
Now I have a pretty stubborn colloid suspended in a sodium hydroxide solution, which can be filtered.
Any suggestions as to how I can isolate the vanadium from it?
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blogfast25
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[*] posted on 10-11-2012 at 11:00


I presume you dissolved the AlV alloy in NaOH, leaving the vanadium unreacted, right?

Try neutralising the solution with sulphuric acid. The neutrality and higher ionic strength of the new solution might 'break' the colloid.




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Mixell
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[*] posted on 10-11-2012 at 11:26


Well, not exactly.
At first I rinsed the alloy in nitric acid, which turned it into a powder (which I thought was pure vanadium).
Then I turned to rinsing the powder in a concentrated sodium hydroxide solution, which dissolved excess aluminium and turned the vanadium powder to a colloid.
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[*] posted on 10-11-2012 at 13:34


Surprisingly enough, the sulfuric acid started dissolving the colloid (with hydrogen bubble evolution).
The solution acquired a yellowish tint (probably due to Vanadium in it's +5 oxidation state).
I had to neutralize it to prevent the vanadium from dissolving.
Hopefully I'll get a nice powder at the bottom of the beaker tomorrow morning, if not, I'll probably get rid of this witches stew.
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[*] posted on 10-11-2012 at 18:11


15% aluminum, balance vanadium?

I'm surprised HNO3 did anything to it, it doesn't corrode aluminum normally and I'd think it would dissolve the vanadium if anything.

At room temperature, aluminum is in solid solution up to 65%at, so assuming the vanadium is still elemental, you will indeed have something rather fine and impure.

Best bet, get it all in solution, separate the two chemically and crystallize or precipitate a purified vanadium compound. Now, if you want metal again, have fun with that...

Can vanadium be plated from solution under reasonable conditions? Electroplating would be the simplest cold method to get pure metal.

If you had, say, a vacuum induction furnace, I might recommend melting the alloy with a mild oxidizer (in the presence of low pressure oxygen, say).

Tim




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Mixell
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[*] posted on 10-11-2012 at 19:12


Well, separating it from the aluminium might be an issue...
Even isolating the vanadium compound itself is quite problematic, if crystallization is not possible. On de-acidifying, a solution of vanadium ions yield a fluffy-colloidal precipitate, which sticks to everything...
The vanadium colloid seems to react to the presence of the sulfate ions/neutral pH. Hopefully I'll manage to isolate something out of it.

In the mean time I will probably try obtaining red selenium from sodium selenite, any suggestions for reducing agents?
I thought about using formic acid/copper (might be a tad slow)/ethanol/Ferrous solution.
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[*] posted on 10-11-2012 at 19:18


Vanadium (III) sulfate might be a good candidate for separation, seems like it isn't that soluble in water. While aluminium sulfate is quite soluble.
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[*] posted on 10-11-2012 at 22:16


Do V(III) ions resemble Al ions? They may coprecipitate or substitute.

If vanadium isn't in solution yet, NaOH will carry aluminate away, of course you have that colloid to contend with. Dissolve the vanadium and you'll probably get the same problem with vanadate-aluminate mixtures.

V(III) or V(IV) will be the handiest; which compounds crystallize nicely, chlorides probably hygroscopic, what about sulfate?

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Mixell
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[*] posted on 11-11-2012 at 05:30


Vanadium ions are soluble at high pH, so NaOH might carry it away too.
Vanadyl sulfate (VOSO4) might be indeed nice to have, but it is very hygroscopic, so I assume it is quite soluble too.
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[*] posted on 11-11-2012 at 05:48


I'm fairly sure that you can dissolve V2O5 in aqueous ammonia to get some sort of ammonium vanadate but Al(OH)3 will not dissolve in dilute ammonia solution.

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[*] posted on 11-11-2012 at 05:54


Well, I don't have V2O5... I think I'll try the sulfate method if the colloid yields nothing.
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[*] posted on 11-11-2012 at 06:59


It's not clear what you have, but if you dissolve the lot in dilute acid, oxidise it with whatever's cheap (bleach is a reasonable candidate) then add an excess of ammonia the Al will ppt and the V will dissolve.
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[*] posted on 11-11-2012 at 07:17


Quote: Originally posted by 12AX7  

Can vanadium be plated from solution under reasonable conditions? Electroplating would be the simplest cold method to get pure metal.



Heat-boosted V2O5 thermite works very well. Gets you lump metal too. And of course it's quite spectacular to watch!




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[*] posted on 11-11-2012 at 15:36


Hm, I do have some impure aluminium metal, and I never did a termite reaction before...
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[*] posted on 13-11-2012 at 06:37


I agree with blogfast, if you can make your vanadium solution into V2O5 thermite is a good way to get the metal! Here's a short clip of a vanadium thermite I did: http://www.youtube.com/watch?v=-j-7LxavEJ4&feature=plcp

I didn't have any heat boosting in mine, just V2O5 and Al powders. I got a very good sized lump of V out of it, a disk of roughly 3/4 in. diameter. Pretty surprising considering the violence of the reaction!
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[*] posted on 13-11-2012 at 06:56


@Mr HS:

Very interesting: that was nearly a flash powder!

I calculated that the V2O5 thermite would need a little boosting to reach 2,500 C (well above the MP of alumina and V metal) and added 0.1 mol of KClO3 (per mol V2O5, plus required Al, plus CaF2) and it ran smoothly but slower than yours. The slag/metal separation was fairly good but not perfect. Will have to revisit that one day...

Do you still have the vanadium obtained?



[Edited on 13-11-2012 by blogfast25]




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[*] posted on 13-11-2012 at 16:21


Hmm, when adding something like KClO3, remember that the KCl byproduct is gaseous at reaction temperatures. Nevermind, I suppose KClO3 is too... :D

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blogfast25
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[*] posted on 14-11-2012 at 13:52


Quote: Originally posted by 12AX7  
Hmm, when adding something like KClO3, remember that the KCl byproduct is gaseous at reaction temperatures. Nevermind, I suppose KClO3 is too... :D

Tim


Tim, surely you remember my titanium dioxide chlorate/nitrate/sulphate boosted thermites over at the ABYMC forum? :D Halcyon days!

KClO3 is industrially used in quite a few aluminothermic reactions. It's perfectly OK.

[Edited on 14-11-2012 by blogfast25]




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[*] posted on 14-11-2012 at 18:57


Ahhh, so I do! :D Though I'd argue KNO3 is more.... minerally?! Who am I kidding, it makes molecular nitrogen...

Tim




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blogfast25
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[*] posted on 15-11-2012 at 11:31


Quote: Originally posted by 12AX7  
Ahhh, so I do! :D Though I'd argue KNO3 is more.... minerally?! Who am I kidding, it makes molecular nitrogen...

Tim


I compared KClO3 and KNO3 back-to-back: couldn't tell the difference in those specific conditions.




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Mixell
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[*] posted on 22-11-2012 at 06:26


On the first addition of sulfuric acid, there was observed a light precipitate of greenish color (probably V(III) sulfate). In addition, the solution turned yellow (but still black, due to the colloid).

The colloid was left to stand for a few days, but yielded nothing.

After a further addition of sulfuric acid, the solution cleared up with evolution of bubbles, and a brick red precipitate appeared.

I assume the yellow color is due to V in the +5 oxidation state. And the precipitate should be the infamous "red cake" which is hydrous V2O5.

And I assume the vanadium was oxidized from +3 to +5 due to a presence of molecular oxygen in the solution.

I still have a 400 ml acidic solution containing those (VO2)+ cations with some aluminium and sodium ones.

Any suggestions as to how I can isolate the remaining V2O5 without contaminating it with sodium/aluminium sulfate?
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[*] posted on 22-11-2012 at 08:24


Quote: Originally posted by Mixell  

Any suggestions as to how I can isolate the remaining V2O5 without contaminating it with sodium/aluminium sulfate?


If you feel sure the red precipitate is V2O5 then filtering and washing with copious amounts of water would be a first step. If needed, you could probably purify it further by converting to metavanadate and re-precipitating as V2O5. There's a recent thread on that.

The first filtrate will need an oxidiser to kick the remaining V (III) into V(V).

[Edited on 22-11-2012 by blogfast25]

[Edited on 22-11-2012 by blogfast25]




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[*] posted on 26-11-2012 at 07:25


@blogfast25: Sorry for the slow reply, but yes I do still have my thermite vanadium! I'll post a picture when I get home, assuming my computer cooperates. I had to reformat recently and lost Photoshop, which was on a CD borrowed from a friend :(

Edit: here's the photo. The large lump is 3/4" on the longest side, and the backside of it looks black like the smaller pieces. The colorful oxidation is pretty interesting!

Thermite Vanadium.jpg - 178kB

Amazing how much harder it is to just simply re-size a photo without Photoshop :/

[Edited on 11-27-2012 by MrHomeScientist]
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