## 3 Results and Discussion
### Chemical Make-Up via X-ray Fluorescence (XRF)  
The x-ray fluorescence characterization of CO-Dolo, HP-Dolo (see Figure 1) and their calcined counterparts were carried out to explore the chemical constituents in terms of bulk weight percentages. Table 1 below gives the compositional variations of these samples in terms of constituent compounds and their wt%. By reviewing the Table 1, it is very clear that the HP-Dolo has the active content of CaO and MgO combined to be only \(\sim\)56%, and the other 44% from inert compounds (e.g., SiO\({}_{2}\)\(\sim\)32% and Al\({}_{2}\)O\({}_{3}\)\(\sim\)7%) which have no value added to the overall calcination and carbonation processes. Whereas, the CO-Dolo counterpart showed \(\sim\)88% of the mixtures of CaO and MgO that could fully contribute to the bi-metal carbonate [CaMg(CO\({}_{3}\))\({}_{2}\)] formation. Therefore, our further results of HP-Dolo samples with lower reported values in terms of percentage of mass conversion may be impacted due to their reported lower purity level. More remarks about the XRF are stated in Table 1.  
Figure 1: Snapshot camera pictures of (**a**) commercial dolomite sample; (**b**) handpicked dolomite sample. Compositional Mapping via Automated Scanning Electron Microscopy-Energy Dispersive X-ray Spectroscopy (SEM-EDX) Mineralogy  
The XRF results as reported in Section 3.1 are at the elemental or compound wt% level. For example, we have given the wt% of CaO and MgO and other oxide phases. The Loss on Ignition (LOI) correction is often needed while analyzing the XRF, in order to account for the volatile compounds, in this case, CO\({}_{2}\) locked in the dolomite [CaMg(CO\({}_{3}\))\({}_{2}\)] matrix [42, 43]. Therefore, a sophisticated and automated mineralogical tool, Automated SEM-EDX Mineralogy with Variable Pressure-Scanning Electron Microscopy (VP-SEM) coupled with four energy dispersive X-rays (EDX) at the Colorado School of Mines was deployed to study the compositional mapping of all our samples listed in the experimental section and are tabulated in Table 2. Five different samples such as HP-Dolo, ball-milled HP-Dolo-BM, carbonated under nitrogen HP-Dolo-STFN2, carbonated under air HP-Dolo-STFO2 were studied for compositional mapping and are represented in Figure 2. \begin{table}
\begin{tabular}{c c c c c c c} \hline \hline
**Elements or Compounds** & **CO-Dolo** & **CO-Dolo-STF** & **HP-Dolo** & **HP-Dolo-STF** & **Remarks** \\  & **wt\%** & **wt\%** & **wt\%** & **wt\%** & **wt\%** & **Remarks** \\ \hline CaO & 67.90 & 34.26 & 36.60 & 32.00 & \begin{tabular}{c} -50\% reduction in CaO content in HP-Dolo. \\ After carbonation in STF, the CaO content \\ increased in the range from 3.5 to 17 wt\% \\ More or less equal amount of MgO in both \\ samples. After carbonation in STF, the MgO content is reduced in the range from 1.7 to 8.3 wt\% \\ HP-Dolo contains large amount of silica \\ (sand type). After carbonation in STF, the SiO\({}_{2}\) content reduced up to 8 wt\%. \\ P\({}_{2}\)O\({}_{5}\) & 0.52 & 0.60 & 1.61 & 0.83 & P\({}_{2}\)O\({}_{5}\) in trace amounts in all samples \\ Fe\({}_{2}\)O\({}_{3}\) & 9.94 & 9.33 & 2.53 & 3.88 & \
\begin{tabular}{c} Fe\({}_{2}\)O\({}_{3}\) is greater in CO-Dolo due to \\ purification procedures. \\ Al\({}_{2}\)O\({}_{3}\) \\ \end{tabular} & - & - & 6.66 & 5.07 &
\begin{tabular}{c} Alumina Al\({}_{2}\)O\({}_{3}\) is found in Earth-mined \\ phosphates, HP-Dolo. \\ Added row 1 and row 2 values. \\ -30\% mass reduction in HP-Dolo due to \\ unreactive SiO\({}_{2}\). After carbonation in STF, this reactive mixture of CaO+MgO \\ increased by 3-8 wt\%. \\ Loss on Ignition is due to the CO\({}_{2}\) release \\ during calcination. \\ \hline \hline \end{tabular}
\end{table} 
Table 1: X-ray Fluorescence data for both commercial and handpicked dolomites. Figure 2: Automated Scanning Electron Microscopy-Energy Dispersive X-ray Spectroscopy (SEM-EDX) analysis of five different dolomite samples done at Colorado School of Mines (CSM).