Utilizing microbial-induced carbonate precipitation technology and carbonation for recycling municipal solid waste incineration fly ash in the production of bricks
Juanling Cui, Shenhao Xie, Guanhua Jia, Yifan Yan, Wei Liu, Zhu Li
Abstract
Bio-processing can be used to modify municipal solid waste incineration (MSWI) fly ash (FA), to reduce its heavy metal leaching capacity and environmental impact, allowing its reuse as a construction material. Microbial urease catalyzes the hydrolysis of urea to CO 3 2- and urease-producing bacteria convert heavy metal ions into low mobility heavy metal carbonates, while also converting Ca 2+ into calcite through electrostatic attraction . This study aimed to solidify the heavy metals in MSWI FA for the production of microbial MSWI FA bricks (MMBs), using microbially induced calcium carbonate precipitation (MICP) and carbonation , establishing the mechanisms of solidification and hydration. The produced MMBs were characterized by XRD and SEM-EDS, with the pore structure and porosity characterized by NMR and the heavy metal ion leaching concentrations determined via toxicity characteristic leaching procedure (TCLP) tests. The results demonstrated that the application of MICP and carbonation can improve mechanical properties of MMB specimens. Finally, the flexural and compressive strength of MMB specimens were increased by 103% and 54%, respectively. MICP produced calcite can partially fill pores smaller than 4000 nm, In addition, calcite produced from carbonation can enhance the pore filling effect. The leached concentration of heavy metal ions from MMBs was reduced to below the Chinese standard threshold limit, which was lower than that of MSWI FA, with a maximum reduction of 58%. In the preparation process of MMBs, the use of MICP technology can not only use MSWI FA instead of cement to prepare bricks, but also solidify and stabilize heavy metals in the preparation process, save the amount of cement required to solidify MSWI FA, and achieve double saving. Carbonation can further use CO 2 to improve the mechanical properties of MMBs and reduce carbon emissions . The result is a sustainable benefit that saves energy and protects the environment.