Mechanochemical processing of landfilled coal fly ash for enhanced CO₂ sequestration and heavy metal immobilization in sustainable hydraulic cements

Abstract

ABSTRACT This study developed an energy-efficient, sustainable, and economical method for capturing carbon dioxide using landfilled coal fly ash. The innovative approach processes captured carbon dioxide with supplementary additives and alkali activators to produce a new class of hydraulic cement. A total of eight cement formulations incorporating varying proportions of landfilled coal fly ash, calcium-containing industrial byproducts, and alkali activators were produced and experimentally tested. The study achieved significant CO₂ uptakes, reaching up to 8.35% by weight of the raw materials. Up to 99.98% immobilization efficiency of heavy metal (copper) was recorded along with a significant increase in the total dissolved solids and conductivity. FTIR spectroscopy confirmed CO₂ incorporation with notable peaks at 1400 cm− 1 and 1063 cm− 1, indicating carbonate species. SEM and EDS analyses revealed varied morphologies, with dense, interconnected particle networks in some of the cement formulations. Compressive strength tests showed all formulations exceeded the EPA’s minimum requirement of 0.34 MPa, with the highest strength reaching 38 MPa at 28 days. The findings of this study point to the viability of the production of mechanochemically processed hydraulic cements in CO₂ environment with effective carbon sequestration capability, marked heavy metals immobilization characteristics, and enhanced physical and mechanical attributes.