Effect and mechanism of CO2 mineralization on the performance of geopolymer from municipal solid waste incineration fly ash

Research on waste management and CO 2 mineralization has always been a hot topic. While the effect of carbon dioxide mineralization on cementitious materials was well understood, the mineralization potential of geopolymers from municipal solid waste incineration fly ash (MSWI FA) remained poorly characterized. This study systematically investigated the effects of pressure and pre-curing time on CO 2 uptake and the properties of geopolymers from MSWI FA. The research revealed that CO 2 uptake in these geopolymers ranged from 2.01 to 3.12 wt%, with increased CO 2 pressure or reduced pre-curing time leading to an increase in CO 2 uptake. Notably, the mineralization reaction predominantly occurred within the first 60 min, aligning with a diffusion-controlled model where the CO 2 mineralization reaction products obstructed reactants and pore structures, resulting in a rapid decline in reaction rates. The average pore size and porosity of the geopolymer (P2(D3)) dropped by 82.6 % and 32.6 %, respectively, following CO 2 mineralization, but the RBO value rose by 18.1 %. These changes indicated improvements in the pore structure and the degree of polymerization of hydration products, contributing to the early strength of the geopolymer (23.4 MPa at 7 days). Based on various characterizations, the mechanisms of CO 2 mineralization on geopolymers from MSWI FA were categorized into three aspects: inhibition of geopolymerization, decalcification of CSH gel, and the filling effect of carbonates. This research offers novel insights into promoting resource utilization of MSWI FA and reducing CO 2 emissions. • The product layer diffusion model effectively described the mineralization reaction. • CO 2 mineralization facilitated the early compressive strength of geopolymers. • Mineralization did not greatly affect the leaching concentrations of heavy metals. • The mechanism of mineralization on geopolymers could be divided into three aspects.