Understanding of Interactions Between Pyrolysis Gases and Liquid Aluminum and Their Impact on Dross Formation

Organic contaminated aluminum scraps have to be recycled in an economical, effective and ecological way. It is state of the art to remove organic coatings by thermal pre-treatment under reduced oxygen atmosphere, which can be achieved in multi chamber furnaces. If the organic coating is not removed completely during pre-treatment, gasification can continue while the scrap is submerged into the melt. Subsequently, undesirable gas-melt reactions cause an increase of dross formation and a decrease of metal recovery. This work aims to improve the understanding of interactions between pyrolysis gases and liquid aluminum as a scientific basis to reduce oxidation losses. Experiments were performed in a lab-scale furnace with injection of synthetic pyrolysis gases (CO₂, CO, C_xH_y) into molten aluminum. Thermochemical calculations, off-gas and dross structure analysis were performed to support the evaluation of the experimental findings. The paper presents qualitative and quantitative results about the impact of reactive gases on oxidation of aluminum melts and finally derives a mechanism model.