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

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 CaSO₄, CaCO₃, CaOHCl, Ca(OH)₂, NaCl, KCl and SiO₂, alongside Si-bearing phases, such as clinotobermorite (Ca₅H₈O₂₁Si₆) and sanidine (KAlSi₃O₈). 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.