In many countries around the world, the thermal treatment of waste plays an important role in the waste-management system. As a result, electricity and heat are produced. However, solid residues are produced in the form of bottom ash, fly ash (FA) and air pollution control (APC) residues. Alternative raw material resources are currently being sought, one of which may be anthropogenic materials from waste thermal treatment processes. This paper presents the results of a study on the trace element content of FA and APC residues from three different installations: municipal solid waste incineration (grate boiler), sewage sludge (fluidized bed boiler) and hazardous waste (rotary kiln). Research methods such as ICP-MS (inductively coupled plasma mass spectrometry), ICP-AES (inductively coupled plasma/atomic emission spectroscopy) and XRD (X-ray diffraction) were used. The results obtained indicate that the chemical composition of FA and APC residues depends mainly on the type of waste being converted, the thermal process and the flue gas treatment method. Ash from sewage sludge incineration in particular contains significant amounts of P and Sb – elements classified as critical raw materials (CRM). In addition, they also contain other valuable metals such as Ag and Zn, in amounts far exceeding the average crustal abundance. In addition, residues from the incineration of hazardous waste may pose a potential risk to the environment due to the presence of significant amounts of heavy metals such as Pb, Cd and Hg.