Extraction of metallic aluminum from fluidized bed and grate incineration bottom ash

The extraction of metallic aluminum from incineration bottom ash (IBA) has twofold implications: to obtain aluminum for the recycling industry and to reduce the content in the treated mineral fraction for its utilization as aggregate in concrete. This study used IBAs from fluidized bed (FB) and grate (G) municipal solid waste incineration for two full-scale experiments, investigating the flows of metallic aluminum in a dry-wet IBA treatment process. Metallic aluminum >4 mm was determined by hand sorting, while <4 mm was determined by the soda-attack method. Extraction rates into metal concentrates of 97% for FB-IBA and 78% for G-IBA were achieved, demonstrating the plant's ability to treat both types of IBA. The elevated extraction rate for FB-IBA is attributable to the dry IBA discharge and the reduced bed temperature. These factors preclude the melting of aluminum, glass, and minerals, resulting in the presence of aluminum particles that are entirely liberated from the mineral phase of IBA, which is advantageous for eddy current separation. Consequently, low residual metallic aluminum contents in the treated mineral fraction (0-8 mm) of 0.5 wt-% in FB-IBA and 1.0 wt-% in G-IBA were determined. Nevertheless, to draw conclusions on the usability in concrete, it is imperative to implement continuous monitoring of the residual metallic aluminum content to substantiate these values, given their reliance on sound plant operation as well as on the initial IBA composition, which knowingly exhibits significant fluctuations.