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Author: Subject: Electrical purification of clays
Polverone
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smile.gif posted on 10-6-2004 at 11:34
Electrical purification of clays


I just recently recalled my only venture into electrochemistry that was an unqualified success:

When I was seven years old, I was at my grandparents' house during Christmas vacation and my uncle, who is a soil scientist, was there too. He showed me something that I found fascinating: adding some thick mud from the ground to water and then applying DC current caused a very silky, fine-textured clay to accumulate on the cathode, from which it could be periodically scraped. I accumulated a film canister full of superfine clay this way, which I still have stored somewhere.

According to the brief web-reading I just did, clays often are structured such that they have a net negative charge that is balanced out by other ions around them. Under the influence of electricity, I guess those ions and the clays go their separate ways.

I can't think of any particularly "mad" uses for this technique, but it seemed (and seems) almost magical that such a simple procedure can separate in such purity one component from a mixture of mud, organic debris, pebbles, sand, etc. If you ever have a chance to entice young children with the wonders of science and technology, I think this is a worthy alternative to the usual water-splitting electrolysis demonstration.




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kryss
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[*] posted on 10-6-2004 at 12:49


I know certainly here our clays have loads of Iron in them - if you want to get rich work out a way of seperating the Iron and alumina out from them - lots of people have tried unsuccessfully.
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Cyrus
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[*] posted on 10-6-2004 at 12:56


Quote:
Originally posted by Polverone

Under the influence of electricity, I guess those ions and the clays go their separate ways.


Pardon me if this is a ridiculously stupid idea, and I have a feeling it is, but if all the positive ions went to one side, and the negatively charged clay went to the other side, and you put the clay in a bottle, wouldn't you have a net negative charge in the bottle?:o I thought that the solution would tend to equalize the charges... some positive ions should stay near the clay.

So if you tried the same thing with NaCl, and partitioned off the negative side of the cell, and got rid of the water, you would have a bunch of Na+? Is that even possible?

Ok, I realize that the clay molecules are much larger per charge and so the charge is less important, but still, this seems weird.




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Marvin
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[*] posted on 11-6-2004 at 05:30


Locally things will always be balenced. So seperating NaCl, the Na+ and the Cl- move apart, but the Na+ is locally balenced by OH-, and the Cl- is balenced by the H+. The solvent alowing you to do the electrolysis has to do this, or it wouldnt be ionising.
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Cyrus
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[*] posted on 11-6-2004 at 12:21
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Marvin, the H+ and the OH- you speak of, do the come from the autoionization of water or from electrolysis?

If they are from autoionization, then you could easily "overload" them with Na+ and Cl- ions,

if they are from electrolysis, what if you used a voltage that was not large enough to break down water? Would no ions flow anywhere, even though they are being attracted to the anode/cathode?




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[*] posted on 13-6-2004 at 03:33


Hm. It would be great if one could get the gallium out of the clay instead. Perhaps it is concentrated in your "superfine clay". Not that there is much to begin with.
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