Dual Role of Low-Cost Indirect Carbonation: Effective Carbon Sequestration and Decalcification Purification of Dechlorination Wastewater 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.