Comprehensive study of physicochemical and environmental properties of Air pollution control residues from UK energy-from-waste facilities

• This work bridges key gaps with the most comprehensive APCr data compiled to date. • UK APCr predominantly releases Pb, Ba, Mo, Cr, Zn, Cu, chlorides and sulphates. • Pb and chloride leaching from UK APCr often exceeds Waste Acceptance Criteria. • 45 minerals were identified in APCr, including 21 newly detected, some Si-bearing. • UK APCr shows minimal environmental risk from organic pollutant leaching. Thermal treatment of Municipal Solid Waste in Energy-from-Waste (EfW) facilities enables energy recovery and landfill reduction but generates hazardous air pollution control residues (APCr). This study characterised 42 APCr samples from 22 UK EfW facilities, integrating compositional, mineralogical, leaching organic fraction and microstructural analyses to assess environmental implications. Scanning Electron Microscopy – Energy Dispersive X-Ray Spectroscopy (SEM-EDS) identified major elements (>0.1 wt%): O, Ca, Cl, Si, Al, Mg, Fe, K, Na, P, S and Zn. Inductively Coupled Plasma – Optical Emission Spectroscopy quantified total metal concentrations (mg/kg): Zn (>1,000), Cu and Pb (>100), As, Ba, Cd, Cr, Ni and Sb (< 1,000) and Mo (<100). X-Ray Diffraction identified 45 mineral phases, including 21 newly reported in APCr. Dominant phases comprised CaSO 4 , CaCO 3 , CaOHCl, Ca(OH) 2 , NaCl, KCl and SiO 2 , alongside Si-bearing phases, such as clinotobermorite (Ca 5 H 8 O 21 Si 6 ) and sanidine (KAlSi 3 O 8 ). Leaching tests showed environmental risks from Pb, Ba, Mo, Cr, Zn, Cu, chlorides and sulphates, with Pb and chlorides mostly exceeding hazardous Waste Acceptance Criteria (WAC). Organic indices showed Total Organic Carbon predominantly undetected, Loss on Ignition mostly below hazardous WAC and Dissolved Organic Carbon absent in most leachates, indicating that organics largely remain within the solid phase. SEM imaging revealed fine-grained material (0.1–1 µm), diverse particle morphologies and inclusions of unburnt organics, carbon and metals. Findings inform APCr treatment strategies for safe handling, recycling and resource recovery.