[Athrax]

Hi!

For an experiment I need about 300g of finely powdered CaCO₃.
Unfortunately all I got is Ca(OH)₂, and plenty of it. Nothing easier
than that, I thought. Just dump it all into a large container, add
water, bubble air through it, using an aquarium air pump.

Unfortunately nothing ever is as easy as it seems, CO₂ concentration
in air is just 0.03%, and my setup has been bubbling away happily for two
months now (yes I'm somewhat patient) and still is very heavily alkaline.

Investing money is not an option, so my only CO₂ source unfortunately
probably will have to be air. Is there any way to speed up the reaction
in a reasonable way? Boiling the Ca(OH)₂ solution in a large stainless
steel pot comes to mind, perhaps?

Best regards,
-Athrax

[Borek]

Why not add source of CO₂ somewhere - any flame will do.

[Enthalpy]

Does alkalinity prove anything? If 1/10 of the original hydroxide remains, the solution will be alkaline.

400ppm=0.04% presently. 300ppm was before we burned fossil fuel. 300g carbonate needs 3mol CO₂ or 7500mol air, that's 170m³. An aquarium air pump bubbling 50mm³/s (or?) would take a century IF all dioxide reacted thanks to an excellent contact with the lime. Ouch.

Looks like you need a better setup. But why should the carbonate cost anything? Depending on where you live, you find it in the soil.

[Elric82]

Can’t you get calcium chloride and sodium carbonate? I just got about 15 kilograms of the chloride for free, and about 1.5 kilograms of the carbonate for a couple dollars. You can just make a solution of each and do a double replacement reaction. You might even already  have the chloride salt if you live in a cold climate. It’s used for treating sidewalks in winter time

CaCl₂ + Na₂CO₃  CaCO₃ + 2NaCl

For some reason, I can’t get the subscript button to work correctly.
I’ve tried several times

Edit by Borek: corrected formatting.