Carbon dioxide sequestration by mineral carbonation via iron complexation using bipyridine chelating ligands

An innovative mineral carbonation method was developed to synthesize iron(II) carbonate (FeCO₃) by cation complexation using 2,2'-bipyridine as ligand. First, complexes of iron(II) and different ligands were theoretically analyzed and discounted in terms of their temperature and pH-dependent stabilities, iron-ligand interactions, possible by-products and difficulty of analysis, choosing 2,2'-bipyridine as the most suitable ligand. Then, the Job plot was used to verify the complex formula. The stability of [Fe(bipy)₃]²⁺ at pH 1-12 was further monitored for 7 days using UV-Vis and IR spectroscopy. Good stability was observed between pH 3 and 8, decreasing within pH 9-12 where the carbonation reaction occurs. Finally, the reaction between Na₂CO₃ and [Fe(bipy)₃]²⁺ was performed at 21, 60, and 80 °C and pH 9-12. The total inorganic carbon measured after 2 h shows that the best carbonate conversion (50%) occurred at 80 °C and pH 11, being the most suitable conditions for carbon sequestration. SEM-EDS and XRD were used to examine the effect of synthesis parameters on the morphology and composition of FeCO₃. The FeCO₃ particle size increased from 10 μm at 21 °C to 26 and 170 μm at 60 and 80 °C respectively with no pH dependence. In addition, EDS analysis supported the carbonate identity, whose amorphous nature was confirmed by XRD. These results would help prevent the iron hydroxide precipitation problem during mineral carbonation using iron-rich silicates. These results are promising for its application as a carbon sequestration method with a CO₂ uptake of around 50% obtaining Fe-rich carbonate.