chornedsnorkack
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Metals water to amalgam to metal
Are there any metals which cannot be separated from aqueous solutions by electrolysis followed by distilling off quicksilver?
Even alkali metal can be reduced to amalgam out of aqueous solution - with Na it is a routine industrial method. Can K, Li, Rb and Cs likewise be
reduced to their amalgams out of aqueous solution?
If you can, what next? Alkali metals form multiple high melting intermetallic compounds (Hg2Na melts at 352 degrees), and release lots of heat on
reaction with quicksilver - so much that quicksilver can heat to boiling!
It follows that in order to boil off the quicksilver, a lot of heat needs to be applied. But sodium itself does boil only at 890 degrees. Still -
potassium is 760, and rubidium and cesium only 700 or so.
Can quicksilver be boiled off alkali metals, or do they form high boiling azeotropes that cannot be purified by distillation?
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elementcollector1
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Amalgams do not form azeotropes, as far as I know. However, any such distillation must be done with the utmost precaution, under vacuum and inert gas.
Also, the max concentration of, for example, sodium in mercury is relatively low.
Elements Collected:52/87
Latest Acquired: Cl
Next in Line: Nd
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vmelkon
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Quicksilver? That's an ancient name. The name is mercury now.
I know that it works for K because I have done electrolysis of KCl solution in water. I would see these specs on the surface of the mercury dancing
around and emitting hydrogen.
It would most likely work for the other alkali metals as well.
I don't know of anyone who has extracted alkali metals that way. You would need a vacuum setup to reduce the boiling point. The problem would be that
there would be trace amounts of mercury in your alkali metal.
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WGTR
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I'd like to point out a practical aspect of electrolytically-produced amalgams that I don't
hear discussed very often. Back in the day, molten lead cathodes were sometimes used in
the electrolysis of molten sodium salts. One problem that occurred repeatedly was the
formation of a sodium-rich crust on the surface of the lead. This was caused by the fact that
the sodium-lead alloy was less dense than the lead cathode, therefore it would stay on top
unless the lead was either mechanically agitated, or co-deposited electrolytically. If left
to its own devices, the cell efficiency would drop like a rock, as the extra sodium was not alloying
with the cathode.
The Mineral Industry, Volume 7
McGraw-Hill Book Company, 1899
Mercury cells have the same problem due to this less dense alloy that is formed on the surface:
Attachment: Electrolytic_Preparation_of_Sodium_Amalgam.pdf (104kB)
This file has been downloaded 365 times
So basically either the mercury cathode needs to be stirred, or co-deposited by diverting some
of the current through a mercury anode.
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bfesser
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Very interesting. Thank you for the uploads, WGTR.
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chornedsnorkack
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Once you get a solid amalgam precipitated, it precipitates, floats to top and stops the production of metal. So what electrolysis gives is saturated
solution of Hg4Na in mercury, in case of Na.
Hg4Na and all other intermetallics except Hg2Na melt incongruently, so you can get Hg2Na by heating Hg4Na to incongruent melting.
But what you get is then Hg2Na, melting point 352 degrees. Thus 33 atom % and about 5 atom% Na.
The eutectic with pure Na is eutectic with HgNa3, and it has melting point of 21 degrees and composition of 85,2 atom % Na, or about 40 mass %
So what you have is several intermetallides that are high melting, with high heat of formation and low activity and vapour pressure of Hg in melt.
How would you get from 33 atom % Na to over 85 %?
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