Dual Role ofLow-Cost Indirect Carbonation: EffectiveCarbon Sequestration and Decalcification Purification of DechlorinationWastewater from Incineration Fly Ash Pretreatment

How to reduce the amount of NaHCO₃ used in the decalcification of municipal solid waste incineration fly ash (IFA) prewashing wastewater is key to controlling the cost of IFA low-temperature pyrolysis. A novel route is proposed to replace NaHCO₃ with CO₂ and NH₄OH for decalcification and generate vaterite CaCO₃ with a purity of 98.15%. The effects of different chemical additives of NH₄OH, NaOH, and NaHCO₃ on the removal of Ca and heavy metals from IFA prewashing wastewater and on the crystalline phase of CaCO₃ are systematically investigated. Ca-removal rate is near 100% at the molar ratios of NH₄⁺/Ca²⁺, OH^–/Ca²⁺, and HCO₃^–/Ca²⁺, which are 2.5, 2, and 2, respectively. Heavy metals are almost completely removed while the solution is carbonized to form CaCO₃ coprecipitation. The presence of NH₄⁺ favors vaterite formation, while NaOH and NaHCO₃ promote calcite generation. Then, the environmental and economic performances of the three carbonization scenarios with Monte Carlo simulations are evaluated by life cycle assessment with life cycle costing. The use of CO₂ coupling with NH₄OH is always the best choice. Additionally, the successful demonstration of using real incineration plant flue gas decalcification provides a new pathway of IFA prewashing detoxification with short process and low cost without expensive NaHCO₃ additive.