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.

The mining industry, including hard-coal mining, has a significant and multifaceted impact on all components of the environment. One of the factors is the production of various types of waste which, due to their physico-chemical and ecotoxic properties, do not always pose a threat to the environment and can be used in various ways. Such treatment of waste perfectly fits into the concept of the circular economy through the protection of natural resources and the maximum re-use of waste. One of the wastes generated by hard-coal mines is coal sludge from the purification of underground water in surface settling tanks. The article presents the results of research on the physico-chemical and phytotoxic properties of carbon sludges from two settling tanks with regard to assessing the possibility of their re-use in the reclamation of degraded areas. These sludges contain mainly sand fractions. An analysis of their chemical composition revealed the presence of heavy metals. Leachability studies have shown that despite the high concentrations of metals, a small quantity of these metals passes into the solution. In this respect, therefore, they do not pose a threat to the environment. However, a threat may result from the presence of chlorides and sulphates, the amounts of which are influenced by, among other factors, the time of waste storage in the settling tank. Phytotoxicity tests performed on garden cress ( Lepidium sativum) did not show a toxic effect at any concentration of the water extract. In addition, for one of the sludges, water extracts with concentrations starting from 12.5 and 50% stimulated the growth of the plant’s shoots and roots, respectively. The results show that the tested coal sludges may be used in appropriate doses for reclamation work, for example, when establishing a plant cover.