The cement industry accounts for approximately 5 - 8% of global anthropogenic CO₂ emissions, primarily due to limestone calcination and fossil fuel combustion. In the context of decarbonization targets, Carbon Capture Utilization and Storage (CCUS) via mineral carbonation represents a promising pathway for permanent CO₂ sequestration and resource utilization. This research, part of PRECIZE project (ADEME/IMERYS), investigates an innovative process to integrate CO₂ and rich flue gases from hydrogen combustion with waste gypsum to produce high-value materials. A flexible steady-state modelling framework was developed by coupling PHREEQC (using the Thermoddem database) with a customizable Excel-based mass balance interface. The tool enables rigorous thermodynamic equilibrium and ion speciation calculations while incorporating iterative convergence algorithms for recycle streams.