Unlocking the mysteries: Investigating the kinetic mechanism of calcium carbonate formation from phosphogypsum

Abstract

Apparent inconsistencies exist in the comprehensive utilization of sulfate, indicating a lack of systematic investigation into the relationships between reacting conditions and the structures of materials. This study quantifies the coprecipitation and transformation process during dissolution-carbonation from phosphogypsum (PG) to polymorphs of calcium carbonates (CaCO3) in the presence of NaOH, NH3, and CO2 through a two-step process. The research establishes a framework for characterizing resulting solutions and achieving products. Additionally, the kinetic mechanism of CaCO3 preparation and PG carbonation was established using a new atomistic KMC model, which reconciles discrepancies and predicts dissolution modes approaching equilibrium. Particularly, it predicts the structures and stability of CaSO4 hydrates by leveraging differential solubilities at a molecular level. Subsequent carbonation with CO2 and the calculation of equilibrium relationships under controlled conditions resulted in the production of CaCO3 from CaSO4·2 H2O. Model simulations and parameter optimization for precursors, intermediates, and generators were monitored and compared over time using RS and powder EPR experiments, yielding optical information for investigating the kinetic mechanism. The findings highlight that PG-involved pathways play a role in purification and mineralization, emphasizing the need to reevaluate traditional concepts of utilizing calcium-rich waste and capturing CO2.