IMPROVING THE REACTIVITY OF MUNICIPAL SOLID WASTE INCINERATED BOTTOM ASH THROUGH WET CARBONATION

Abstract

Municipal Solid Waste Incineration (MSWI) produces significant quantities of bottom ash (IBA), which poses environmental challenges due to high alkalinity, variable composition, and the potential leaching of heavy metals. The aim of this work is to improve the reactivity of municipal solid waste incinerated bottom ash through wet carbonation. IBA samples from two UK facilities plants (Cornwall and Wilton) were characterized in terms of particle size distribution, pH, thermal behavior, CO₂ uptake, and leaching properties. Wet carbonation experiments were conducted under controlled conditions, exposing moistened IBA to CO₂ rich environments until pH stabilization. Analytical techniques, including Thermogravimetric Analysis (TGA) and Inductively Coupled Plasma Mass Spectrometry (ICP-MS), were employed to quantify carbonate formation and assess heavy metal immobilization. The results showed that IBA was predominantly sand-sized, with finer fractions exhibiting higher reactivity and alkalinity. Wet carbonation effectively reduced pH from >11 to ~6–7 and achieved significant CO₂ uptake through the formation of stable carbonates, primarily calcium carbonate. Heavy metal leachability was substantially reduced, with decreases of over 90% for Cu, Zn, Pb, Cd, and As. However, antimony concentrations increased post-treatment, indicating that targeted mitigation strategies are required for certain oxoanion forming elements. Variations in carbonation efficiency between the two sources highlighted the influence of particle size distribution and initial composition. This study demonstrates that wet carbonation is a promising approach for stabilizing MSWI-BA and enhancing its suitability as a supplementary cementitious material. The process aligns with circular economy principles, reduces landfill dependency, and contributes to greenhouse gas mitigation through CO₂ sequestration. Recommendations are provided for process optimization, source-specific protocols, and policy integration to support large-scale implementation.