**3. Carbon dioxide storage**

Once captured, CO2 can be compressed and transported by shipment or *via* pipelines to storage destinations in the ground (geological sequestration), oceans (still in probation phase), or as mineral carbonates (considered as both utilization and storage process) [4] (**Figure 1**).

In *geological storage*, CO2 is injected under high pressure into stable rocks rich in pores that trap natural fluids at a depth between 0.8 and 1 km. Different trapping mechanisms, temperatures, and pressures can be employed allowing the storage of CO2 as liquid, compressed gas, or in its supercritical condition, subject to the characteristics of the reservoir. Geological formations include unmineable coal seams, depleted oil, and gas reservoirs.

In contrast, *mineral carbonation* or metal carbonate formation involves the direct or indirect reaction between CO2 and a metal oxide such as Ca and Mg, naturally found as silicate minerals. Aside from the availability of minerals, the advantage of this technology is the production of stable carbonates that are suitable for long period of storage that can last for centuries without leakage. The other benefit is the direct use of CO<sup>2</sup> from flue gas without the costly need of establishing a pure stream, since other gas impurities such as NOx do not influence the carbonation reaction. The large-scale applications of this method are not fully developed yet and still encountering a high overall cost [4, 9].
