Insights into the usage of biobased organic acids for treating municipal solid waste incineration bottom ash towards metal removal and material recycling

The recycling of incineration bottom ash (IBA) is crucial for sustainable municipal solid waste (MSW) management and alleviating landfill burdens. However, limited environmentally friendly methods exist to effectively treat IBA for safe recycling. This study systematically examined the performance of biobased organic acids, namely citric acid (CA), oxalic acid (OA), lactic acid (LA), and levulinic acid (LEA), for IBA treatment. CA shows high extraction efficiency for most trace metals (e.g., Mn > 65 %, Pb > 50 %, Co approx.100 %, Cd > 85 %, Zn > 80 %, Ni > 80 %), while OA performs better for certain trace metals (e.g., Sn approx.99 %, Sb > 70 %, Mo > 70 %, Cr > 50 %). Multivariate statistical analysis and instrumental techniques were used to gain deeper insights into the critical mechanisms, including proton promoted dissolution, ligand related dissolution and precipitation/co-precipitation. The latter two mechanisms are distinctive metal extraction behaviours by organic acids compared to their inorganic counterparts. Both CA- and OA-treated alkaline-washed IBA residues demonstrate high leaching reduction efficiency (>99.9%) of the critical heavy metals, making the treated IBA residues suitable for safe recycling as construction materials. This study highlights the potential of environmentally friendly organic acids which can be derived from bio-wastes for treating and repurposing IBA as resources for construction materials, promoting sustainable waste management for MSW incineration ash.