Land Use and Geo-Engineering - Introduction to Carbon Capture and Sequestration - page 533

Box 11.3. 2 Olivine weathering
Olivine is a mineral (see fi gure) with the formula (Mg,Fe) 2 SiO 4 . It is a common min-
eral in the earth's subsurface but weathers quickly on the surface. The weathering
reaction is:
(Mg, Fe) 2 SiO 4 + 4CO 2 + 4H 2 O → 2(Mg 2 + , Fe 2 + ) + 4HCO 3 − + H 4 SiO 4
Image by Azuncha (2006), WikiCommons : http://en.wikipedia.org/wiki/File:Peridot2.jpg
Direct air capture
In Chapter 4, we computed the minimal energy required to separate CO 2
from fl ue gas. These calculations showed that separation from a stream
with a lower CO 2 concentration requires more energy per CO 2 molecule.
For example, compared to capturing a CO 2 molecule from a coal-fi red
power plant, the minimum energy to capture the same molecule from air
will be a factor of fi ve higher.
The idea in Direct Air Capture is similar to that in capturing CO 2 from
fl ue gasses; we fl ow air over a material that selectively adsorbs CO 2 .
Because of the low concentration of CO 2 in air, we need a material that