yuno
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Aluminium amalgam
Hello,
I recently did well known synthesis of aluminium isopropoxide. For those who hear this name for the first time it is a useful reagent in organic
chemistry and is prepared by reacting aluminium amalgam (Al/Hg) with isopropyl alcohol.
After distiling al-isopropoxide under reduced pressure I was left with black residue which is composed of (I think) aluminium oxide and some mercury
salts. I was not happy about dumping that down the drain so I wonder what would be the best way to recycle mercury and avoid polluting environment?
Aluminium amalgam is useful reducing agent and in some experiments like this cannot be replaced (note that I do not have money to buy gallium and
prefer to work with mercury). Not that someone will need tons of this amalgam but it is useful to know how to deal with this problem.
Sorry for my English and thanks everyone who joins discussion!
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kristofvagyok
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Welcome,
I would like to ask first that what kind of Al/Hg did you used? It was from chem. supplier or it was prepared by you? If the second, then did you used
aluminum foil? If yes, then you should know that in the commercial Al-foil (what is used in the kitchen) a lot of impurity is present e.g.: iron and
other metals what could cause the black color.
And just a short note: if pure chemicals are used (abs. propanol) then no Al2O3 should form during this reaction.
And for disposing the toxic waste, just mix it with some sulfur.
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yuno
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I prepared amalgam myself, very much followed this procedure:
http://www.youtube.com/watch?v=axxbIWOge_o
Yes I used aluminium foil, I can only get pure aluminium powder and reaction with powder would be too violent. There isn't much about this reaction or
similar reactions using Al/Hg on the internet. I searched for reaction mechanism but couldn't find anything. My error, I wanted to write aluminium
hydroxide not oxide because when Al/Hg is used as reducing reagent aluminium hydroxide is formed as byproduct.
Well for me it's not waste, I don't live on large deposits of mercury  I needed
to make that mercury(II)chloride! I want to recycle that mercury. I have few ideas on that, for example, dissolving residue with some acid and then
bubbling hydrogen sulfide through solution to precipitate mercury(II)sulfide. I just want to see what others think.
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chemrox
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Everybody uses aluminum foil. Like the man says; S or S and Zn. Or collect your hazardous stuff and take it to an appropriate disposal site. Pay
the nickel-take the ride.
"When you let the dumbasses vote you end up with populism followed by autocracy and getting back is a bitch." Plato (sort of)
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weiming1998
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Dissolve the black, mercury-filled residue in excess concentrated HCl. Any resulting precipitate is most probably impurities in Al that doesn't
dissolve in acid (most likely Si), Hg or Hg2Cl2. You can remove Si by rinsing precipitate in dilute NaOH. That results in some mercury oxides and
elemental mercury, with you can keep. Then take the dissolved solution, reduce with Al foil, and rinse precipitate/amalgam in NaOH again. That gets
rid of excess Al. Now keep the Hg and dispose of remaining solution normally.
[Edited on 4-7-2012 by weiming1998]
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AJKOER
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To see the stuff in your Al foil, soak it for about an hour in vinegar (we are trying to remove a plastic coating). Rinse and place in a container of
aqueous ammonia. You will see tiny bubbles as the protective Al2O3 layer is circumvented by the rise in pH and the Al reacts with water forming H2 and
a clear gelatinous Al(OH)3 (saturated with aqueous ammonia). In about a day or two, all that will remain is a black residue (Carbon or Silicon I
suspect).
If you decide to burn your Al foil and repeat the experiment, you are left with the same thing, but the dissolving in ammonia may take a little less
time.
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unionised
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"To see the stuff in your Al foil, soak it for about an hour in vinegar (we are trying to remove a plastic coating)."
What plastic coating?
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yuno
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Quote: Originally posted by weiming1998  | Dissolve the black, mercury-filled residue in excess concentrated HCl. Any resulting precipitate is most probably impurities in Al that doesn't
dissolve in acid (most likely Si), Hg or Hg2Cl2. You can remove Si by rinsing precipitate in dilute NaOH. That results in some mercury oxides and
elemental mercury, with you can keep. Then take the dissolved solution, reduce with Al foil, and rinse precipitate/amalgam in NaOH again. That gets
rid of excess Al. Now keep the Hg and dispose of remaining solution normally.
[Edited on 4-7-2012 by weiming1998] |
How do you mean reduce it with Al foil?
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barley81
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I think it's best that you dispose of the waste at a recycling center. The tiny amount of mercury in the residue isn't worth your time.
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weiming1998
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| Quote: Originally posted by yuno | | Quote: Originally posted by weiming1998 | Dissolve the black, mercury-filled residue in excess concentrated HCl. Any resulting precipitate is most probably impurities in Al that doesn't
dissolve in acid (most likely Si), Hg or Hg2Cl2. You can remove Si by rinsing precipitate in dilute NaOH. That results in some mercury oxides and
elemental mercury, with you can keep. Then take the dissolved solution, reduce with Al foil, and rinse precipitate/amalgam in NaOH again. That gets
rid of excess Al. Now keep the Hg and dispose of remaining solution normally.
[Edited on 4-7-2012 by weiming1998] |
How do you mean reduce it with Al foil? |
First dissolve your precipitate in HCl (as I described), then add Al foil directly to the solution. You will need an excess because the remaining HCl
in the solution can attack it. Mercury (initially black suspension, but precipitates into shiny liquid) will form and will not be attacked by HCl.
Some might amalgamate with the aluminum, which, in that case, add some more HCl to dissolve aluminum.
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barley81
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I don't think mercury can coalesce so easily from a suspension - the black precipitate made by adding ammonia to calomel never became shiny mercury in
my class...
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