ChemNub
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Displacement of Zn from ZnCl2 with Al
So I've been attempting to obtain some zinc powder for later potential use for reduction and such by dissolving chunks of relatively pure zinc metal
in HCl and then precipitating zinc from the resultant ZnCl2 solution with aluminum foil in a simple displacement.
Unfortunately the al foil will not react and thus no zinc precipitate  . I'm
presuming this is due to a coat of aluminum oxide that is preventing the al metal from even coming into contact with the solution, but am not entirely
sure. Perhaps there is something else I am missing? Would using freshly filed aluminum ball bearings or something of that sort be more effective?
very frustrating to be stumped by something seemingly so simple, any help would be appreciated!
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bbartlog
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I would expect the zinc to coat the aluminum. You speak of precipitating the zinc, but since the aluminum is not in solution to start with the only
place the zinc is going to come out is at the interface, i.e. the surface of the foil. There might be some trick to get around this but in general I
don't think that you will be able to precipitate elemental zinc by simple means.
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ChemNub
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hmm that is a good point.. I will put it over gradual stirring to see if it makes a difference- otherwise will just spring for a dremel file and take
straight to these chunks 
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Polverone
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I thought I had posted about this several years ago, but I cannot find an earlier message about it... perhaps I mentioned it somewhere else.
I have reacted aqueous ZnCl2 with aluminum foil. If there is considerable free HCl left in the solution, the foil reacts rapidly but much of it goes
to hydrogen and aqueous AlCl3, and the zinc formed wants to dissolve again. If there is very little free acid left, it can be difficult to get the
reaction started. When there is a little free acid left the reaction starts fairly readily and not too much foil is wasted.
A porous zinc foil is formed by this reaction. The foil needs to be washed of salts and acid after it forms.
It is fairly reactive; I once accidentally ignited a bunch of these zinc foils in my mother's kitchen trying to dry them in a pan on low heat over the
stove.
I had produced the ZnCl2 solution using technical hydrochloric acid on pennies with an initial dash of H2O2 to pierce the copper shells. Perhaps there
is some catalytic trace of copper that helps too, though it all seemed to be reduced by the zinc back to (dark, irregular) metal in the solution.
If you want to try this, as best I recollect:
The initial acid was about 30%, the cheap colored material sold for cleaning masonry and lowering swimming pool pH.
15 minutes of acid acting on excess of zinc (pennies): too much acid left
2 hours of acid acting on excess of pennies: about the right amount of acid left, to see foil react without excessive delay
2 days of acid acting on excess of pennies: too little acid left, or perhaps solution just needed to be warmer as it got from the initial zinc-acid
reaction -- in any case I was not able to see a reaction with foil within 10 minutes or so
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Sedit
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Not really on topic but I find the best means to pierce the shell of the copper is to just wack it with a hammer. Either that or nick it with a pair
of dikes. I remember hearing somone around here making mention of using a file to remove a small section of the coating then heating them to melt the
low MP zinc rightout of the shell but I have never tryed this method as of yet since I have ready access to galvinized steal and that workd pretty
well for all my ZnCl2 needs. My only issues has always been achieving dry ZnCl2. It always boils down to a syrup instead of forming any sort of
crystals.
Any suggestion on that note?
Knowledge is useless to useless people...
"I see a lot of patterns in our behavior as a nation that parallel a lot of other historical processes. The fall of Rome, the fall of Germany — the
fall of the ruling country, the people who think they can do whatever they want without anybody else's consent. I've seen this story
before."~Maynard James Keenan
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