Dross Formation in Aluminum Melts During the Charging of Beverage Can Scrap Bales with Different Densities Using Various
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https://doi.org/10.1007/s11837-020-04268-4 2020 The Minerals, Metals & Materials Society
ALUMINUM: RECYCLING AND CARBON / ENVIRONMENTAL FOOTPRINT
Dross Formation in Aluminum Melts During the Charging of Beverage Can Scrap Bales with Different Densities Using Various Thermal Pretreatments JAN STEGLICH
,1,3 BERND FRIEDRICH,2 and MARCEL ROSEFORT1
1.—TRIMET Aluminium SE, Aluminiumallee 1, 45356 Essen, Germany. 2.—IME Process Metallurgy and Metal Recycling, RWTH Aachen University, Intzestr. 3, 52056 Aachen, Germany. 3.—e-mail: [email protected]
Herein, dross formation (D) in used beverage can (UBC) scrap bales was investigated in laboratory-scale experiments to understand the reactions of solid can coating residues with aluminum melts. The experimental conditions were chosen according to a multi-chamber furnaces process, in which thermal pretreatment and submerged melting of the scrap bales are combined. The thermal pretreatment results show that the supply of oxygen should be continuously adjusted to meet the oxygen demand of UBC scrap bales for thermolysis. Moreover, it is necessary to maintain the UBC scrap bales at an effective material temperature of 550–570C for at least 30 min. It is shown that adhering carbon-containing pyrolysis char and oxidized can sheet surfaces decrease the coalescence of molten scrap, resulting in dross with a high metal fraction. Further melting experiments with UBC scrap bales of different densities (q) show that by lowering the q, the dross formation reduces.
INTRODUCTION AND MOTIVATION Aluminum beverage cans are widely used, and the can market is continuously growing. After the use and disposal of these cans, the valuable aluminum metal must be recycled to produce new cans to satisfy the requirements of an eco-friendly circular economy. The metallurgical recycling of used beverage can (UBC) scrap is a combined process of thermal pretreatment used to remove the can coating and melting. The melting of scrap still poses a challenge to aluminum recyclers as it leads to metal loss and undesirable dross formation (D). Open questions are how the organic content, coating residues, and UBC scrap bale density (q) affect D. As the dross formation reactions are quite complex, this investigation focuses only on the can coating and its residues in UBC scrap bales after pretreatment. The influence of oxygen in the common furnace atmosphere was excluded by performing the laboratory melting experiments under an inert atmosphere.
(Received April 14, 2020; accepted June 30, 2020)
LITERATURE REVIEW Can Coating Removal and Residue Waterborne epoxy, polyester, and acrylic polymer resins are widely used as beverage can coatings. Bisphenol-a-diglycidyl ether (BADGE)-based epoxy resins are examples of the commonly used coatings in the can industry. The curing temperature of waterborne resins is in the range of 150–200C depending on the resin-cure system and time.1,2 When the curing temperature of a thermosetting polymer exceeds this range, the cross-linked polymer network starts to degrade at
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