## 4 Discussion  
The experimental results showed that the volumetric rate of the CO\({}_{2}\) feed determines the amount of carbonate formed in the reactor; in the first experiment, the CO\({}_{2}\) was fed to the reactor at a rate of 1.5 mL min\({}^{-1}\). However, when the volumetric flow rate was increased at 15.2 mL min\({}^{-1}\), the mass of the precipitated metal carbonate was increased. In contrast, as the feed rate increased to 94.7 mL min\({}^{-1}\), a decrease in precipitated carbonate was found. So, it was determined that the best capture conditions and CO\({}_{2}\) sequestration correspond to a flow of 15.2 mL min\({}^{-1}\). In addition, the recommended reaction time corresponds to 20 min, because at higher reaction times, a greater proportion of bicarbonates appears. The capture of CO\({}_{2}\) in aqueous solutions for carbonate formation is a complex gas-liquid reaction system, presenting several series stages of mass transfer and reaction. The analysis of the pH behavior during the first 10 min of reaction shows that the pH of the solution presented a slight decrease, which suggests that at the beginning, the reaction is controlled by CO\({}_{2}\) mass transfer from the gas phase to the liquid phase by solubilization. Then, CO\({}_{2}\) gradually reaches the semi-stationary state, followed by the formation of dissociated carbonic acid in aqueous solution, generating two protons and the carbonate ion that reacts with the cation Ba\({}^{+2}\) or Sr\({}^{+2}\) to form the corresponding carbonate. Then, that reaction generates a rapid decrease in the solution pH that is observed as a change in the slope of the pH where carbonate formation exists. Thereafter, the transformation of carbonates to bicarbonates occurs at pH values lower than 8, this behavior is consistent with the stability of chemical species at different pH values according to the carbonate system [16]. Furthermore, if we consider that the reaction is exothermic, the linear increase in temperature suggests that the reaction rate is constant during the first 40 min of the reaction. The highest amount of CO\({}_{2}\) capture was obtained with the solution of Ba(OH)\({}_{2}\), and according to the results of X-ray diffraction, the solid formed is Ba carbonate with a high purity, which was confirmed by comparison with reference card PDF 00-005-0418, JCPDS. In addition, the diffractogram shows narrow, intense peaks that strongly suggest that the (SrCO\({}_{3}\)) obtained had formed with good crystallinity. In addition, the scanning electron microscopy results show the shape of the acicular crystals, which are of micrometric size, and the results of the elementary analysis confirm the presence of the elements that make up the carbonates of Sr and Ba. The results of  
Figure 10: TGA thermogram of the solids recovered from carbonation reactions with Sr(OH)\({}_{2}\). infrared spectroscopy of the different carbonates present the well-defined signals of the characteristic bands of weak, medium, and strong intensity for the carbonates of Sr and Ba. Dry carbonate samples were analyzed by TGA, and the results show that they are stable up to 900 \({}^{\circ}\)C. This agrees with the values reported by some authors, in which the thermal decomposition temperature of BaCO\({}_{3}\) is above 1000 \({}^{\circ}\)C; meanwhile, that of the commercial BaCO\({}_{3}\) is from 1140 to 1198 \({}^{\circ}\)C in an Ar atmosphere [21], from 1000 \({}^{\circ}\)C in an air atmosphere [22], and from 1300 \({}^{\circ}\)C, it decomposes into barium oxide and carbon dioxide [24]. The alternative of using minerals such as serpentine, olivine, and wollastonite as a mineral capture matrix is necessary to condition it by means of steps including crushing, sieving, washing, and activation, which is difficult for small companies to implement. So, the use of solutions of metal hydroxides, industrial waste, and metallurgy seems to be viable to obtain these carbonates, thus increasing the storage capacity of CO\({}_{2}\).