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Author: Subject: How to filter highly basic solutions?
testimento
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[*] posted on 19-1-2014 at 13:52
How to filter highly basic solutions?


I'm gonna need to make sodium hydroxide myself because it is banned too in my country due to "cookery". I was planning to mix sodium carbonate and calcium hydroxide to crash out CaCO3 and NaOH. The problem with this stuff is mostly the basicity. Concentrated NaOH's favorite food are organic(paper) and mineral(glass) based filter materials. Maybe one method could be to settle the CaCO3 and then decant the clear solution off, evaporate and oven dry it?
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DraconicAcid
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[*] posted on 19-1-2014 at 14:00


Filter it when it isn't concentrated.



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testimento
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[*] posted on 19-1-2014 at 14:43


If the pH of 1L is 13, it must be increased to 10L to get it down to 12, and to 100L to get it down to 11, so Im not gonna do that.
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forgottenpassword
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[*] posted on 19-1-2014 at 14:54


Filter paper is fine. It doesn't dissolve on contact with NaOH.
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papaya
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[*] posted on 19-1-2014 at 15:09


Take a funnel, put a *wet* cotton ball into hole (tight) and filter everything - alkaline, acidic, etc.. works well even for small particles.
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[*] posted on 19-1-2014 at 18:25


Paper is probably OK if the mixture is dilute and cool (see also, glass). Otherwise, I'd use glass wool packed in a funnel. If you have them, glass fiber filters or fritted funnels are good, too. Just make sure to rinse them well immediately after use to prevent permanent fusing/clogging of the frit.

Obviously, an inert membrane would be best, but those might be hard to get (and, they can clog easily, so a prefilter is well advised).

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O3




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testimento
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[*] posted on 19-1-2014 at 20:13


I think Im gonna do the settling thing. I usually do this by pouring the stuff into a plastic tank with lid on the side and let the CaCO3 settle on the bottom to render a clear liquor which can be drained. I can tell by experience that CaCO3 forms a slurry with water that will just simply clog any filter imaginable, maybe except slow sand filters.
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[*] posted on 20-1-2014 at 12:56


Quote: Originally posted by testimento  
I think Im gonna do the settling thing.


Of course. Very alkaline solutions really do screw up paper, as I've experienced several times. Quite a lot can be achieved by decantation alone and filtering does have drawbacks too.




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smaerd
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[*] posted on 20-1-2014 at 14:12


Yea I had really bad times filtering through paper of pH 12+ solutions especially if they had fine particles or were large in volume. Diatomaceaus earth can be used for fine particles but it will become soluble in very alkaline environments iirc.



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testimento
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[*] posted on 21-1-2014 at 14:32


Since essentially the Na2CO3 solubility is 455g/l at 100C and CaOH is very low, one should yield 30-50% NaOH solution, which will be cooled, but anyway the pH is far more near 15 than 12 so it will certainly eat paper like nothing.
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bismuthate
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[*] posted on 21-1-2014 at 15:00


You could boil it down then add 100ml or 50ml of ethanol to dissolve some NaOH then decant that, dilllute it and filter it.
(well I think that would work anyway)
Other than that carefully:).




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forgottenpassword
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[*] posted on 21-1-2014 at 15:15


Quote: Originally posted by testimento  
the pH is far more near 15 than 12 so it will certainly eat paper like nothing.
I'm sure it won't change your mind, but anyway:

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[*] posted on 21-1-2014 at 18:31


You could try a centrifuge, it would seppirate the calcium carbonate and the hydride. To make one tie a string from a blade of a fan to a tightly closed vial and turn on the over head fan.
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testimento
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[*] posted on 22-1-2014 at 05:13


ForgottenPW, I won't question your link. I don't see filtering as a bad option, but because I have experience in clarifying by settling especially with CaCO3 and have equipment for that, and the volume to be filtered is unavoidably large(several liters, at minimum), I'd prefer settling.

Centrifuge would work with proper equipment at hand. Unfortunately, I don't have a centrifuge on hand that can roll 10 liters of stuff per batch. Settling does the same job, and I'm not getting paid for this shit so I can left it settle for overnight if necessary. My previous tests conclude, though, that 10 liters of CaCO3 suspension will usually settle within few hours crystal clear.
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[*] posted on 22-1-2014 at 08:08


Quote: Originally posted by forgottenpassword  
Quote: Originally posted by testimento  
the pH is far more near 15 than 12 so it will certainly eat paper like nothing.
I'm sure it won't change your mind, but anyway:

You can both be right. Paper based filters are much more damaged by sodium hydroxide while cotton based filters such as the one you referenced are pretty resistant to sodium hydroxide.
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