Investigation on the Cl− and heavy metals stabilization of MSWI fly ash by incorporating Portland cement and carbonation

Abstract

To achieve CO₂ and municipal solid waste incineration fly ash (MSWI-FA) utilization in construction and building materials production, in this study a novel carbon mixing method was proposed to prepare cement-MSWI-FA pastes with improved properties. The effect of carbon mixing and curing on the compressive strength, Cl⁻ as well as heavy metal solidification and pore structure was investigated. The reaction products were analyzed with XRD, SEM-EDS and TG to reveal the role of CO₂ mixing on the phase assemblage development. The results showed that a ‘1.5 min normal mixing followed by 1.5 min carbon mixing’ procedure allowed the cement paste with 60 % MSWI-FA to obtain a compressive strength reaching 20 MPa at 28d. Compared with carbon curing, carbon mixing allowed easier and homogenous CO₂ diffusion, and thus increased the CO₃²⁻/HCO₃⁻ in the pore solution for the formation of CaCO₃ and Mc. The CaCO₃ functioned as filler to refine the pore structure and thus contributed to the compressive strength improvement, while the Mc was converted to the Fs and AFt with the presence of Cl⁻ and SO₄²⁻ at 28d, enhancing the Cl⁻ and heavy metals solidification. The proposed method and the test results of this study can provide technique support for the utilization of CO₂ and MSWI-FA.