[smathew]

I am doing a science fair project and have a question about the limestone cycle. A typical limestone cycle has 3 parts given below:

Cycle - Part 1:
              CaC03 + Heat -> Ca0 + C02

Cycle – Part 2:
              Ca0 + H20 -> Ca(OH)2

Cycle – Part 3:
              Ca(OH)2 + CO2 -> CaC03 + H20

The question is - Can Part 2 of the above cycle be skipped i.e. the part that requires water? And shorted the cycle as:

Cycle - Part 1:
              CaC03 + Heat -> Ca0 + C02

Cycle – Part 2:
              Ca0 + CO2 -> CaC03

Appreciate help in this.

Thanks
SMathew

[Borek]

Reactions are OK, but would that be still called limestone cycle? And would it be practical to use dry CaO as a mortar?

[smathew]

Thank you for the reply. For the project, I plan to use limestone to capture CO2 from the air. If possible, I would like to avoid using water. Can this be practically achieved?

Thanks

SMathew

[Borek]

While not impossible I doubt it will be efficient and practical. Water definitely speeds up reactions involved, and it is much easier to work with liquids than with the dust.

[Enthalpy]

I just wonder what the benefit would be, since CaO is obtained from CaCO₃, from which CO₂ is released by heat. If the goal is to reduce the CO₂ concentration in the atmosphere globally, releasing first as much CO₂ provides no gain. Or did I misintepret? Reduce the CO₂ concentration just locally? Other goal?

One process that absorbs CO₂ uses instead silicates from rocks. If M is a metal like Ca, Na₂, Mg, K₂... the MSiO₃ rock put in contact with CO₂ transforms in MCO₃ and SiO₂, simplifying much. It consists in tapping the unwanted pure CO₂ exhaust of a power plant or a CaO factory, compress it and inject it in well chosen rock formation. Even that simple process, where CO₂ is already concentrated and very little more is done, is presently asleep because emission bonds are too cheap for it.

Water consumption: I'm pretty sure that finely divided CaO absorbs any residual moisture from the air, whatever dry the atmosphere is, even in the worst desert. So CaO put in very fine contact with the air for CO₂ absorption would find its water too.

Beware of the danger of CaO and Ca(OH)₂ in the air. At some point you need an intimate contact with the atmosphere, which means a fine powder. Alas, Ca(OH)₂ is caustic and CaO is worse. These things have nothing to do in your lungs, not even in small amount. Check the health literature about making CaO and using it in cement.

[smathew]

While not impossible I doubt it will be efficient and practical. Water definitely speeds up reactions involved, and it is much easier to work with liquids than with the dust.

Thank you for the help.

[smathew]

I just wonder what the benefit would be, since CaO is obtained from CaCO₃, from which CO₂ is released by heat. If the goal is to reduce the CO₂ concentration in the atmosphere globally, releasing first as much CO₂ provides no gain. Or did I misintepret? Reduce the CO₂ concentration just locally? Other goal?

Thank you for the suggestions and guidance.

The plan is to capture the CO₂ released when heating CaCO₃ and propose using it for industrial use.
 

One process that absorbs CO₂ uses instead silicates from rocks. If M is a metal like Ca, Na₂, Mg, K₂... the MSiO₃ rock put in contact with CO₂ transforms in MCO₃ and SiO₂, simplifying much. It consists in tapping the unwanted pure CO₂ exhaust of a power plant or a CaO factory, compress it and inject it in well chosen rock formation. Even that simple process, where CO₂ is already concentrated and very little more is done, is presently asleep because emission bonds are too cheap for it.

Thank you for the suggestion of using silicates. I select CaCO₃ because of the availability in nature. I will study at the availability of silicates.

Beware of the danger of CaO and Ca(OH)₂ in the air. At some point you need an intimate contact with the atmosphere, which means a fine powder. Alas, Ca(OH)₂ is caustic and CaO is worse. These things have nothing to do in your lungs, not even in small amount. Check the health literature about making CaO and using it in cement.

Thank you for the warning.

Regards
SMathew