Glycine-induced synthesis of vaterite by direct aqueous mineral carbonation of desulfurization gypsum

Climate change is urgently calling for rapid methods to capture atmospheric carbon dioxide (CO2). CO2 can be sequestred into gypsum from gas desulfurization by carbonation to produce calcium carbonate (CaCO3). However, CaCO3 is produced as a mixture of polymorphs including calcite and vaterite polymorphs, which limits applications. Therefore, we present here a method to produce CaCO3 enriched in the vaterite polymorph. We reacted CO2 with gypsum from gas desulfurization in the presence of glycine. Carbonation products were analyzed by X-ray diffraction, scanning electron microscopy, electrospray ionization mass spectrometry, and Fourier transform infrared spectroscopy. Results show that vaterite content increases from 60 to 97% with increasing glycine concentration from 0 to 20 wt% and then kept a constant value, indicating that glycine promotes the formation of vaterite by inhibiting the growth of the calcite polymorph. We also observed that the intermediate glycinate calcium played a major role in stimulating vaterite growth. Overall, nearly pure vaterite was synthesized successfully by carbonation of gypsum in the presence of glycine.