## 2 Experimental and Theoretical Methods
### Physicochemical Characterizations of Dolomites  
In general, multiple metrological and mineralogical techniques have been employed to characterize the different stages (plain commercial and handpicked dolomites and their calcined counterparts) of dolomite samples at room temperatures. Some of these techniques are powder X-ray diffraction, X-ray fluorescence, Fourier-Transform Infrared Spectroscopy (FTIR), automated scanning electron microscopy with energy dispersive X-ray spectroscopy, thermogravimetric analysis, and BET surface area analysis. The experimental conditions of these techniques and the parameters used to study the dolomites are elaborated in detail in the following paragraphs.  
A number of physicochemical characterizations have been carried out and the results are reported in terms of structural, microstructural, chemical, compositional, and thermal properties during calcination and subsequent carbonation reactions. The chemical composition, structural and microstructural characteristics of the dolomite minerals was studied using different techniques such as X-ray Fluorescence (XRF, Rigaku--NEX/QC/Quantez), Fourier-transform infrared spectroscopy (FTIR), and scanning electron microscopy with energy dispersive X-ray spectroscopy (SEM, EDS). All these metrological techniques confirmed the high percentage of dolomite mineral phase in the earth abundant phosphatic pebbles. The Fourier-Transform Infrared Spectra of the dolomite samples have been characterized using Agilent's CARY 600 FTIR spectrometer (Agilent Santa Clara, CA, USA). The Thermogravimetric analyzer (TGA/DSC 1, STAR\({}^{\text{\textregistered}}\) system), from Mettler Toledo (Columbus, OH, USA), was used to calculate the activation energy for calcination and carbonation of the dolomite pebbles in nitrogen (N\({}_{2}\)) and carbon dioxide (CO\({}_{2}\)) at temperatures up to 800 \({}^{\circ}\)C. The structural phase analysis of the dolomite minerals was observed using X-ray diffractometer (XRD) (Rigaku Mini Flex 600, Rigaku, Tokyo, Japan) with the parameters of 40 kV, current of 44 mA, wavelength (\(\lambda\) = 1.540591 A) of X-ray beam corresponds to copper K\({}_{\alpha}\) line, scan speed of 0.1001\({}^{\circ}\)/min and step width of 0.0100\({}^{\circ}\). The ball-milling method was used to downsize (to micrometer size particles) the handpicked dolomite samples under DI water or another solvent medium. Not all the samples were milled before subjected to characterization techniques. Particle size and surface area were measured using XRD and N\({}_{2}\) adsorption BET method (Quantachrome Instruments, Autosorb, Acquired by Anton Paar Quanta Tec Inc., Boynton Beach, FL, USA).  
The commercial, handpicked, and ball-milled dolomite samples and their carbonated oxide phases via STF were analyzed using automated scanning electron microscopy (automated mineralogy tool manufactured by TECAN, Brno, Czech Republic, at the Colorado School of Mines (CSM). Samples were loaded into the TECAN (Automated SEM-EDX Mineralogy)-VEGA-3 Model LMU VP-SEM platform and analysis was initiated using the control program TIMA3. Four energy dispersive X-ray (EDX) spectrometers acquire spectra from each point or particle with a user defined beam stepping interval (i.e., spacing between acquisition points), an acceleration voltage of 25 keV, and a beam intensity of 14. Interactions between the beam and the sample are modeled through Monte Carlo simulation. The EDX spectra are compared with spectra held in a look-up table allowing a mineral or phase assignment to be made at each acquisition point. The assignment makes no distinction between mineral species and amorphous grains of similar composition. TIMA software was deployed to study the semi-quantitative compositional mapping output results of dolomite minerals at different stages of calcination [39].