Multivariate statistical assessment of critical and trace elements in fly ash from a municipal solid waste incineration plant in southern Poland.

Municipal solid waste incineration fly ash (MSWI-FA) is an environmentally significant residue and a potential secondary source of critical elements, but its heterogeneity and below-detection values complicate geochemical and resource assessment. This study characterized 24 trace, critical, and rare earth element variables in 30 weekly fly ash samples from an MSWI plant in southern Poland. Left-censored observations were treated using Tobit regression before hierarchical cluster analysis (HCA), principal component analysis (PCA), enrichment factor (EF) calculation, and partial least squares (PLS) regression. Mean Zn, Cu, and Sb concentrations were 4255, 358, and 144 mg kg⁻1, respectively. The first two principal components explained 59.8 % of the total variance. Integrated results identified two partly overlapping controls on element distribution: a relatively stable mineral-associated component represented by LREE, HREE, Sc, Li, Mg, and Sr, and thermally driven redistribution and accumulation of selected anthropogenic elements, particularly Sb and Zn. The highest EF values were obtained for Sb (EF = 1910), Pd (EF = 209), Pt (EF = 189), Zn (EF = 166), and Bi (EF = 123). However, Pd and Pt occurred at mean concentrations of only approximately 0.04 mg kg⁻1, and comparison with other installations showed that the investigated ash was not anomalously metal-rich. High EF values therefore do not demonstrate technological recoverability. Zn was identified as the most relevant target for further screening. These internally consistent, but facility- and period-specific, results provide a basis for targeted mineralogical, speciation, leaching, and recovery studies.