Tripropylamine-Assisted Leaching/Regeneration-Mineralization Process for CO2 Sequestration with Concurrent High-Purity CaCO3 Production

Abstract

The combined process of treating alkaline solid wastes and obtaining CO₂ sequestration has recently garnered significant attention. However, studies focusing on low chemical consumption alongside high-purity CaCO₃ production are still limited. Herein, a leaching/regeneration-mineralization process for CO₂ mineralization to concurrently produce CaCO₃ was proposed. First, selective leaching of Ca from municipal solid waste incineration fly ash (MSWI FA) was conducted with the assistance of protonated tripropylamine (TPA) at pH = 10.5, with a concentration of 23,500 mg/L. Concurrently, the protonated TPA was regenerated for subsequent mineralization, completing the mineralization kinetics within 30 min. Temperature had no significant effect on mineralization efficiency or product purity. As the temperature increased, the crystal form transitioned from vaterite to pure calcite. The amount of TPA added significantly influenced mineralization performance, exceeding the stoichiometric ratio allowed for nearly 100% of mineralization efficiency and promoted the transformation of the product’s crystal form toward pure vaterite. Based on experimental results and product characterization, a potential proton transfer-based leaching/regeneration-mineralization mechanism was proposed. Under optimal conditions, the CO₂ sequestration reached 77.5 g/kgFA, yielding 176 g/kgFA of pure CaCO₃. This work offers a promising option for waste disposal, CO₂ sequestration, and CaCO₃ production in a reagent-saving manner.