CO Capture and Storage - Energy and Climate: How to Achieve a Successful Energy Transition - page 117

- mineral sequestration is operated above ground in an

industrial installation by reacting CO 2 with ground rocks or with
solid waste. The main drawback is the need tomanipulate, grind and
store considerable volumes of solid materials. Different solid phases
have been investigated for use in such a process.
Typically, CO 2 is reacted with crushed olivine and serpentine
(magnesium-rich silicate rocks) from a mine. Industrial wastes, such
as blast furnace slag, composed of iron and calcium silicates, can also
be used.

Ex situ

- mineral sequestration is operated by injectingCO 2 in a natural

setting where basic rocks of magmatic origin, such as basalt, are
present. Such an operation is performed in a very similar way to that
used in the case of geological storage. The carbonation reaction
between CO 2 and the surrounding rock occurs very slowly and
results in the formation of a stable compound. The porosity of
magmatic rocks such as basalts is generally low and it is therefore
difficult to inject large amounts of CO 2 .
The porosity and injectivity of such rocks can be increased through
fracturation operations, but such operations are costly and it appears
difficult to use them on a large scale in the near future.

In situ

Carbon dioxide recycling includes all possible uses in industrial or biological
processes. Unfortunately the quantities of CO 2 which can be recycled in that
way are limited. Currently, the main application in the chemical industry is
the production of urea, which requires around 80 million tons of CO 2 per
year [92]. A significant outlet is provided by the agro-food industrywhich, in
Europe, consumes around 2.7million tons of CO 2 .ACO 2 rich atmosphere
is used for accelerating the growth of plants cultivated in greenhouses. This
outlet is also limited, but it is possible to widen the applications of the
biomass produced in a CO 2 enriched atmosphere by investigating new
applications in the agro-food, chemical and energy industries.
The production of algae in bioreactors is presently considered for
sequestering CO 2 produced by a fossil fuel power plant. Such algae can
then be converted into biofuels (diesel from the fatty fractions and/or
ethanol from sugars derived from the biomass). Despite the fact that
this area is very active, it remains difficult to ascertain the economic
competitiveness of these developments.
It is necessary also to assess the overall carbon balance: the combustion
of such biofuels cannot be considered as carbon neutral, because the
carbon used for growing the biomass is provided by a fossil fuel and not
recovered from the atmosphere.