testimento
Hazard to Others
Posts: 351
Registered: 10-6-2013
Member Is Offline
Mood: No Mood
|
|
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?
|
|
|
DraconicAcid
International Hazard
Posts: 4278
Registered: 1-2-2013
Location: The tiniest college campus ever....
Member Is Offline
Mood: Semi-victorious.
|
|
Filter it when it isn't concentrated.
Please remember: "Filtrate" is not a verb.
Write up your lab reports the way your instructor wants them, not the way your ex-instructor wants them.
|
|
|
testimento
Hazard to Others
Posts: 351
Registered: 10-6-2013
Member Is Offline
Mood: No Mood
|
|
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.
|
|
|
forgottenpassword
Hazard to Others
Posts: 374
Registered: 12-12-2013
Member Is Offline
Mood: No Mood
|
|
Filter paper is fine. It doesn't dissolve on contact with NaOH.
|
|
|
papaya
National Hazard
Posts: 615
Registered: 4-4-2013
Member Is Offline
Mood: reactive
|
|
Take a funnel, put a *wet* cotton ball into hole (tight) and filter everything - alkaline, acidic, etc.. works well even for small particles.
|
|
|
Ozone
International Hazard
Posts: 1269
Registered: 28-7-2005
Location: Good Olde USA
Member Is Offline
Mood: Integrated
|
|
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).
Cheers,
O3
-Anyone who never made a mistake never tried anything new.
--Albert Einstein
|
|
|
testimento
Hazard to Others
Posts: 351
Registered: 10-6-2013
Member Is Offline
Mood: No Mood
|
|
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.
|
|
|
blogfast25
International Hazard
Posts: 10562
Registered: 3-2-2008
Location: Neverland
Member Is Offline
Mood: No Mood
|
|
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.
|
|
|
smaerd
International Hazard
Posts: 1262
Registered: 23-1-2010
Member Is Offline
Mood: hmm...
|
|
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.
|
|
|
testimento
Hazard to Others
Posts: 351
Registered: 10-6-2013
Member Is Offline
Mood: No Mood
|
|
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.
|
|
|
bismuthate
National Hazard
Posts: 803
Registered: 28-9-2013
Location: the island of stability
Member Is Offline
Mood: self reacting
|
|
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 .
|
|
|
forgottenpassword
Hazard to Others
Posts: 374
Registered: 12-12-2013
Member Is Offline
Mood: No Mood
|
|
I'm sure it won't change
your mind, but anyway:
Attachment: AN9315600652.pdf (34kB)
This file has been downloaded 406 times
|
|
|
Jmap science
Yet another ID of SimpleChemist-238
Posts: 40
Registered: 19-10-2013
Location: Florida
Member Is Offline
Mood: No Mood
|
|
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.
|
|
|
testimento
Hazard to Others
Posts: 351
Registered: 10-6-2013
Member Is Offline
Mood: No Mood
|
|
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.
|
|
|
macckone
International Hazard
Posts: 2159
Registered: 1-3-2013
Location: Over a mile high
Member Is Offline
Mood: Electrical
|
|
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.
|
|
|
![[*]](images/xpblue/default_icon.gif){kind=icon}
