The single process CO2 capture-mineralization approach integrates methods of CO2 absorption using aqueous solvents and mineral carbonation technology to not only remove carbon dioxide quickly, but also to simultaneously produce precipitated calcium carbonate (PCC). To develop a more sustainable process, it is important to extract calcium from inexpensive raw materials such as industrial by-products. The extractant has a significant effect on the quality of the calcium carbonate produced because it determines the anion paired with the calcium cation. In this work, several calcium sources with different anions (Propionate, Acetate, Nitrate and Chloride) were applied in the single process CO2 capture-mineralization method, and their influence on the polymorph of the obtained CaCO3 was investigated. The CaCO3 produced with inorganic calcium sources predominantly exhibited a calcite structure, while the CaCO3 produced with organic calcium sources had a structure in which vaterite and calcite coexist. This result was in good agreement with our DFT calculations, which indicated the adsorption energy of the organic anions (Propionate and Acetate) were lower than the inorganic anions on the surface of vaterite. Except for chloride with its non-polar nature, in most cases, there was a strong correlation between the polymorph and the adsorption energy calculated for each surface. A mechanism for the polymorph CaCO3 formation in our single process CO2 capture-mineralization method was proposed after observing crystal formation at low concentration.