[adrianN]

Get a large amount of calcium hydroxide in a watery slurry. That absorbs CO2 to form calcium carbonate. Take the carbonate outside and heat it up sufficiently to form calcium oxide and carbon dioxide. Add water to go back to calcium hydroxide.

[swiley]

Be careful with alkali metal hydroxides! They tend to be caustic and mixing them with water is exothermic (it can boil if you do it fast enough.) They will also react with aluminum, potentially violently and can ruin glass.