Sciencemadness Discussion Board

calcium hydroxide >> calcium oxide?

EmmisonJ - 19-3-2009 at 04:33

are there any simple techniques to get calcium oxide from calcium hydroxide?

heating or use of H2SO4? any by-products to be concerned with by the reaction?

not_important - 19-3-2009 at 05:57

Heat will do it, 550-600 C minimum, a slow current of dry CO2 free air helps carry away the water/steam released. Temperatures above 825 C remove the requirement for CO2 free air, as the carbonate decomposes well above that.

Sulfuric acid just gives calcium sulfate, as a first year chemistry book would tell you (hint).

chief - 19-3-2009 at 10:59

The standard technological way is to heat the Ca(OH)2 to 900 [Cels], whereby it decomposes .

EmmisonJ - 20-3-2009 at 04:05

thanks guys

not_important, hint taken :)

no1uno - 4-4-2009 at 00:32

not_important, here are the first pages of some papers (sorry, I'm violently ill or I'd request them first), they are where I got the numbers from before:

I'll try and get back in time to delete this post, fuck I feel "ordinary"

not_important - 4-4-2009 at 05:03

Second paper 1st page is dehdrating the hydroxide at temperatures delow 600 C, while the other paper starts off talking about Ca(OH)2 @ 320 C and CaCO3 @ 510 C - both under vacuum.

Industrially CaCO3 is decomposed at a temperature of 900 to 1300 C. The lower temperature is the theoretical one for full decomposition, the upper is where sintering and other effects reduce the quality of the CaO formed.

Note that industrial processes are trying to get porous pebbles of CaO with as little fines as possible, and often to keep the CO2 concentration in the exit gases high enough to make it a useful CO2 source.

Small scale home production really isn't concerned with either aspect, and external heat with a stream of heated air passed through the CaCO3 allows the use of temperatures below 1000 C. Similarly externally heating Ca(OH)2 to 600 C or so with a slow stream of air to carry off the water works OK, better if you remove CO2 from the air first (unless you don't car about having some CaCO3 in the CaO).

no1uno - 4-4-2009 at 16:43

I'm not quibbling on your point, I was simply showing where I got the ~400C numbers from;). Personally I really don't see too many issues with doing it at home even @800C...