Resource recovery potential of incineration bottom ash fine fraction

Abstract

The paper provides a summary of findings regarding the composition of the fine fraction of incineration bottom ash. While the recovery of metals is common practice for particles larger than 2 mm, it has been less common for finer particles, despite them constituting 30–40 % of the overall bottom ash mass flow. Detailed knowledge of the material composition of this fraction is essential for successful metal recovery. The study utilizes a TIMA electron microscope, originally designed for the mining industry, to analyze the bottom ash. The microscope allows for the identification of chemical speciation and was used to obtain detailed information about particles containing copper (Cu), aluminum (Al), iron (Fe), zinc (Zn), and gold (Au) in the fine fraction below 2,000 µm. Results revealed that metallic aluminum accounts for approximately 15 % of the overall aluminum content, with Al grains often coated by a thin layer of Al₂O₃. Metallic Cu and its alloys make up around 60 % of the copper content, while another 30 % is in the form of Cu oxides. In contrast, there is minimal presence of metallic Fe and Zn in the fine fraction. All metallic Au was bound to a single particle, corresponding to an Au content of 4 mg/kg in the bulk sample. The implications of these results are also discussed in relation to particle size distribution and liberation, as these factors play a vital role in the recovery process.