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Additive-Assisted Indirect Carbonation of Flue Gas Desulfurization Gypsum for High-Purity Vaterite Production under Ambient Conditions.

Abstact
The large-scale generation of flue gas desulfurization gypsum has driven increasing interest in its valorization through mineral carbonation. However, most previous approaches have faced critical limitations, including the reliance on highly concentrated acids or ammonium salts and the requirement for elevated temperature and pressure to produce vaterite. These drawbacks not only increase operational costs but also introduce severe issues of corrosivity, toxicity, and wastewater management. To overcome these drawbacks, this study developed an environmentally sustainable and cost-effective indirect carbonation process to produce high-value vaterite-type CaCO₃ under ambient conditions. Calcium was extracted using a mild 1 M CH₃COONH₄ solution, and carbonation was conducted at room temperature and atmospheric pressure, minimizing chemical and energy inputs. The effects of solvent concentration and trace additives (fluoride and sucrose) were systematically investigated. Results showed that optimized solvent concentrations promoted efficient Ca2⁺ extraction and supersaturation, while small amounts of additives stabilized the vaterite phase and reduced particle size. Notably, combined low-dose F⁻ and sucrose achieved ~ 98% vaterite with enhanced morphology and surface area while minimizing chemical use. This environmentally benign process simultaneously enables CO₂ utilization, waste gypsum valorization, and scalable production of fine vaterite with superior properties, offering clear advantages over conventional methods in terms of sustainability, cost-effectiveness, and product quality.