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Author: Subject: Separation of Mg(OH)2 from Ca(OH)2
kazaa81
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thumbup.gif posted on 5-1-2005 at 16:15
Separation of Mg(OH)2 from Ca(OH)2


Hallo to all,

I've bought a "lime" (is this term correct) which is composed of 50% Ca(OH)2 and 50% Mg(OH)2.
Now, I want to extract/separate Mg(OH)2.....how can I do this?

Thanks at all for help.
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neutrino
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[*] posted on 5-1-2005 at 16:28


You could add a lot of water and hope for the best. Calcium hydroxide is soluble to 1.7g/L water (at 10*C, probably more at higher temperatures), while magnesium hydroxide is soluble to only .0125g/L (room temp). With the common ion effect, you should get a solution of calcium hydroxide and almost no magnesium hydroxide. The problem is that this would require huge amounts of water to be boiled off (you can’t leave it out to dry b/c it will react w/atmospheric CO<sub>2</sub>;).

[Edited on 6-1-2005 by neutrino]
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The_Davster
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[*] posted on 5-1-2005 at 17:27


Add it to dilute sulfuric acid, CaSO4 will precipitate. Filter out the calcium sulfate and add NaOH to the filtrate, Mg(OH)2 will precipitate.

EDIT: Why is this in the organic section?

[Edited on 6-1-2005 by rogue chemist]




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rikkitikkitavi
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[*] posted on 6-1-2005 at 07:16


neutralize the lime mix with HCL to about pH 10.
At this pH only partially Mg(OH)2 is dissolved , but all Ca(OH)2.

Left will also be CaCO3 as solid (always present in Ca(OH)2 to some % ) and this will not dissolve until pH is so low that Mg(OH)2 also dissolves.
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neutrino
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[*] posted on 6-1-2005 at 15:41


Now why didn’t I think of that? If you want to get rid of a pesky ion, just destroy it!:)
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