Metal recovery from bottom ash and its utilization
Bottom ash is the main solid residue from waste-to-energy. The composition of bottom ash reflects the composition of the incinerated waste and depends on the character of the collection area, waste sorting efficiency in the collection area, and the type of buildings in the collection area. The influence of these factors on the content of ferrous and non-ferrous metals and glass was determined based on a detailed analysis of the composition of bottom ash from three waste-to-energy plants in the Czech Republic and the analysis of their collection areas. One of the key factors was found to be the ratio of municipal and commercial trader waste. Higher content of recyclable components such as ferrous and non-ferrous metals was found to be in the bottom ash from big city waste-to-energy plants (e.g. in Prague) that incinerate solely municipal waste (Waste Manage. 2018).
The effective recovery of these metals is due to the wet character of bottom ash technologically intricate. Nowadays, there is a wide variety of different technologies and technological concepts of separation with various demands and efficiency; hence, each technological unit is nearly unique. However, the principles are more or less the same and involve pretreatment steps (aging, sieving, crushing, etc.) with subsequent separation by means of magnetic, eddy current, and sensor-based separators. The state of the art for metal recovery was summarized by an international team in 2020 (J. Hazard. Mater. 2020). Based on the above-mentioned knowledge, a pilot plant with a capacity of several tons per hour was constructed within the Prague WtE plant for the effective recovery of non-ferrous particles over 3 mm. The results from the pilot plant testing and know-how will be used for the construction of a real-scale plant.
Bottom ash after metal recovery can be used in various applications in the construction industry. Possible ways of utilization, as well as technical and environmental criteria setting for safe utilization, are regulated in national law. A comprehensive overview of legislation for bottom ash in Europe and the analysis of criteria for utilization were prepared by the international team in a review paper (Waste Manage. 2020).
- Waste Manage. 73, 360-366, 2018. DOI
- Verified Technology for Separation of Non-ferrous Metals from Incineration Bottom Ash. 2019.
- Equipment for separating non-ferrous metals from a bulk mixture (Utility model) 2019, CZ33130.
- J. Hazard. Mater. 393, 122433, 2020. DOI
- Waste Manage. 102, 868-883, 2020. DOI