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CO₂ mineralization in dye wastewater: Surfactant-free vaterite production for in-situ dye adsorptive removal

Abstact

CO2 mineralization through low-cost calcification into vaterite (CaCO3) presents a promising carbon capture and utilization strategy, offering permanent carbon storage alongside environmental and economic benefits. In this study, we demonstrated a surfactant-free single-pot system for the stabilization of vaterite and its in-situ application for Congo red dye removal. Vaterite formation was investigated by varying Congo red concentrations, where the dye solution served as an indirect carbonation medium, while adsorption performance was evaluated by tuning carbonation time and other key parameters. Highly monodispersed vaterite CaCO3 microspheres were synthesized with > 99% removal efficiency of the dye. Quantitative analysis also depicted an apparent Congo red adsorption capacity of up to 26.78 mg/g, accompanied by CO₂ mineralization of 0.36 g as stable CaCO₃ during the in-situ vaterite formation process. Compared to carbonation in water as the solvent medium, the use of Congo red significantly enhanced the textural properties of the formed vaterite, increasing the BET surface area from ∼0.7 m² g⁻¹ to ∼6.9 m² g⁻¹ . The adsorbed dye onto the surface of the formed vaterite enhanced the surface area, enabling its further application. This work demonstrates a surfactant- and additive-free approach that integrates in-situ CO₂ mineralization with wastewater treatment, highlighting vaterite formation as an effective pathway to simultaneously address carbon capture and dye-contaminated wastewater.