**Figure 16.**

*Calibration curve to calculate mass loss of CO2.*

mass spectrometer data and CO2 mass response is estimated based on the reaction (2NaHCO3 ➔ Na2CO3 + CO2 + H2O). The relationship between peak areas and CO2 mass loss was linear as shown in the CO2 calibration curve (**Figure 16**).

For carbonated samples, the CO2 peak areas were estimated using MS data and then these peak areas are used to determine CO2 mass loss applying the CO2 calibration curve. This CO2 mass loss was used in Eq. (6) to calculate magnesite yield. Eq. (6) is based on the Gadikota formula (4).

Calculating fraction of magnesium (yMg) in dunite

$$\begin{aligned} \text{Yield} \left( \text{Rx} \right) &= \left[ \frac{\text{Measured weight ratio of } CO2 \text{ stored in mineral}}{\text{The residual } CO2 \text{ storage capacity}} \right] \times 100\% \\ &= \frac{\left( \frac{W\_{O2}}{W\_{\text{miss}}} \right)}{\frac{1}{\text{R}\_{\text{O2}}}} \times 100\% \\ &= \text{R}\_{\text{CO2}} \times \left( \frac{\text{TGA}}{(100 - \text{TGA})} \right) \times 100\% \\ &= \text{R}\_{\text{CO2}} \times \left( \frac{\text{TGA}}{(100 - \text{TGA})} \right) \times 100\% \end{aligned} \tag{3}$$

CO2 storage capacity of dunite <sup>¼</sup> <sup>1</sup> RCO2 <sup>¼</sup> *yMg MWMg* <sup>þ</sup> *yCa MWCa* � MWCO2 (4)

$$\text{\textbulletof Mg in MgO} = \left(\frac{\text{MW}\_{\text{Mg}}}{\text{MW}\_{\text{MgO}}}\right) \times 100\text{\%} = \left(\frac{24.3}{40.3}\right) \times 100\text{\%} = 60.3\text{\%}$$

$$\text{\textbulletof MgO in dunite} = 42.6\text{\%}$$

%of Mg in dunite ¼ 60*:*3% � 0*:*426 ¼ 25*:*7% yMg ¼ 0*:*257 using this value in equation 5 ð Þ

Calculating fraction of calcium (yCa) in dunite

$$\text{\%of Ca in CaO} = \left(\frac{\text{MW}\_{\text{Ca}}}{\text{MW}\_{\text{Cao}}}\right) \times 100\text{\%} = \left(\frac{40}{56}\right) \times 100\text{\%} = 71.4\text{\%}$$
