Mapping Rare Earth Element Distribution in MSWI Ash Using Physical Separation and Sequential Extraction

The escalating global demand for rare earth elements (REE) has highlighted the potential of anthropogenic waste streams as secondary resources. This study characterizes the distribution and speciation of REE in Korean municipal solid waste incineration (MSWI) bottom ash (BA) and fly ash (FA). The ashes were subjected to particle size fractionation and magnetic separation to examine REE distribution across different particle sizes and magnetic fractions. In addition, raw BA and FA samples were analyzed using sequential extraction to assess REE speciation and leachability. Elemental composition and mineral phases were determined using inductively coupled plasma optical emission spectrometry (ICP-OES) and X-ray diffraction (XRD). The results show that REEs are enriched in the magnetic fractions of both BA and FA and exhibit slightly higher concentrations in coarser particle fractions. Light REE (LREE) predominate across all particle sizes, including the nonmagnetic fractions. Sequential extraction results show that REEs are predominantly hosted in stable mineral phases, with only a limited proportion present in labile fractions. Overall, these findings reveal the distribution and chemical associations of REE in MSWI ash and provide a basis for future studies on their speciation and potential mobilization.