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Australian University Unveils New Carbon-Trapping Bricks
FirephoxRising writes "A research pilot plant in Newcastle will trial world-first technology that turns carbon emissions into bricks and pavers for the construction industry. More efficient and stable than storing gas in the ground, the new method will sequester carbon and can work anywhere, unlike geo-sequestration which is site specific."
CO2 is carbon at its maximum oxydation level (you cannot burn it anymore). Limestone is made of calcium carbonate (and magnesium carbonate in a lesser extent), it is also carbon at its maximum oxydation level. The transformation seems smart, but it requires water (easy part) and calcium. Where will that calcium come from? The usual source is limestone...
It's been a while since I did chemistry, but calcium carbonate can be made from calcium oxide and carbon dioxide in the presence of water. I think that's more or less how it's done in sea creatures. So you've got:
CaO + H2O + CO2 --> CaCO3 + H2O
I believe the reaction takes place spontaneously when you dissolve calcium oxide and CO2 in water. To check, add up the standard enthalpy of formation for both sides. The water cancels, of course, leaving:
635 kJ/mol + 393.5 kJ/mol --> 1207 kJmol
Right is more negative than the left so the reaction is exothermic. Calcium carbonate is basically limestone or marble, so a nice building material, mixed with other stuff to stabilize it against acid rain. Leaving the question of where you get the CaO.
Having done all that work, I found this: http://www.globalccsinstitute.com/publications/novel-co2-capture-taskforce-report/online/54351.
Looks like the reactions are all exothermic, but you have to come up with the minerals, which means mining a ton and a bit of rock for every ton of coal you burn. But you get building materials out of the bargain too.
A bit of digging finds that they are reacting Olivine (Magnesium silicate) with CO2 giving Magnesium Carbonate.
This reaction has been studied for years as a sequestration reaction for CO2 but traditionally it needs high pressure and moderate temperature to get reasonable
conversion of the Olivine. The team at Newcastle Uni have come up with a method to produce Magnesium Carbonate (Dolomite) at much more modest reaction conditions.