What question did this study set out to answer?

The aim is to analyze the decomposition behavior and metal recovery potential of MSWI fly ash using microwave heating and carbon-based additives.

March 7, 2026Metallurgical and Materials Transactions B0 citationsOpen Access

Decomposition and Microwave Dielectric Characterization of MSWI Fly Ash and the Role of Carbon-Based Additives in Microwave-Assisted Volatile Metal Recovery

ESEdzhe SoyluNorwegian University of Science and Technology DDDanuka Wawita Widanalage DonUniversity of Oulu MOMamdouh OmranUniversity of Oulu

Key Points

The aim is to analyze the decomposition behavior and metal recovery potential of MSWI fly ash using microwave heating and carbon-based additives.
Thermogravimetric analysis (TGA) combined with mass spectrometry (MS) to evaluate decomposition patterns
Dielectric property measurements under varying temperatures to assess microwave responsiveness
Comparison of different carbon-based additives, including graphite, biochar, and blast furnace sludge, on metal volatilization efficiency.
Multi-step decomposition patterns identified with TGA–MS, showing early mass loss due to salts and later carbonate and sulfate breakdown
Microwave responsiveness significantly increased at high temperatures, particularly in sulfide- and Fe-rich samples
Graphite enhanced heating rates the most, while biochar allowed for superior volatilization of metals like Pb and Zn, and BFS showed limited effectiveness.

Abstract

This study evaluates the thermal behavior, dielectric properties, and metal volatilization potential of municipal solid waste incineration (MSWI) fly ash (FA) and air pollution control (APC) residues under microwave heating. Thermogravimetric analysis (TGA), combined with mass spectrometry (MS), and dielectric property measurements were employed to examine decomposition mechanisms and microwave absorption properties. TGA–MS revealed multi-step decomposition patterns, with early mass loss attributed to hydrated salts, followed by carbonate and sulfate breakdown. Zinc was released at both intermediate and high temperatures, depending on the sample composition. Dielectric measurements showed limited microwave responsiveness of raw ashes at low temperatures, with significant increase at high temperatures, particularly in sulfide- and Fe-rich samples. Microwave treatment with carbon-based additives improved heating rates and metal volatilization. Graphite provided the fastest heating due to high conductivity, while biochar achieved superior volatilization of Pb, Cd, Sb, and Zn owing to its reactive and porous structure. Blast furnace sludge (BFS) was less effective compared to other additives, although higher content partially enhanced heating and metal release. Despite high volatilization ratios of the most volatile metals, residues in some cases showed elevated Mg and Zn concentrations due to overall mass loss and retention in refractory phases.

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