Compaction of Aluminium Foil and Its Effect on Oxidation and Recycling Yield

Vallejo-Olivares, Alicia; Philipson, Harald; Gökelma, Mertol; Roven, Hans Jørgen; Furu, Trond; Kvithyld, Anne; Tranell, Gabriella

doi:10.1007/978-3-030-65396-5_96

Cited by 5 publications

(3 citation statements)

References 18 publications

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“…The rate of reaction varies based on several factors, including oxygen availability and atmosphere, but oxidation increases substantially at temperatures above 700 • C [13]. When melting scrap, especially if it has a large specific area, large metal losses occur due to rapid oxidation, resulting in dross formation that floats towards the surface of the metal [14]. The efficiency of the process is reduced as a result.…”

Section: Protection From Oxidationmentioning

confidence: 99%

Solid Salt Fluxes for Molten Aluminum Processing—A Review

Milani

Timelli

2023

Metals

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Aluminum recycling is a promising solution to environmental and economic issues. Secondary aluminum production will rise in the near future; however, the process is not without challenges. Some of the major concerns during remelting of aluminum are the metal losses due to the oxidation of the molten metal and the removal of impurities from the metal bath. The current study summarizes the latest progress in the use of solid salt fluxes for secondary aluminum production and the treatment of molten metal. The chemistry of solid fluxes has been reviewed, with a correlation to their main chemical and physical characteristics, such as density, fluidity, wettability, and reactivity. An overview of the main types of solid fluxes is also provided, with a particular focus on their functions and applications. The efficiency of solid fluxes relies on several factors, including but not limited to the fluxes’ chemical composition and physical properties, flux amount, processing temperature, and flux morphology. The effect of salt fluxes in delivering satisfactory metal cleanliness and sufficient metal recovery has been summarized according to the main flux’s properties.

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Section: Protection From Oxidationmentioning

confidence: 99%

Solid Salt Fluxes for Molten Aluminum Processing—A Review

Milani

Timelli

2023

Metals

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“…Compacting the scrap into bales or briquettes is another standard recycling pre-treatment, since it facilitates storage and transport. A previous study [4] showed that compaction could reduce the oxidation of thin scrap, which has a high specific surface area. The correlation between scrap thickness and re-melting losses was previously described by Rossel [5].…”

Section: Introductionmentioning

confidence: 98%

Thermal De-coating Pre-treatment for Loose or Compacted Aluminum Scrap and Consequences for Salt-Flux Recycling

Vallejo-Olivares

Høgåsen

Kvithyld

et al. 2022

J. Sustain. Metall.

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In aluminum recycling, thermal de-coating pre-treatments remove moisture and organic contamination before re-melting. If the scrap is compacted into bales or briquettes before the thermal treatment and re-melting processes, less surface area is exposed to oxidation in contact with air. However, compaction may also limit the efficiency of the de-coating process. In this study, coated sheets of aluminum were thermally de-coated at varied temperatures and durations. Observations of changes in coating thickness, mass, color, and composition revealed a maximum de-coating efficiency of close to 75% wt due to remaining oxide residues. The relationship between de-coating and compaction was investigated by thermally treating loose shreddings (chips) and briquettes of various densities. The briquettes were compacted by three methods: uniaxial, moderate-pressure torsion (MPT), and MPT at 450 °C (Hot MPT); and the de-coating efficiency was calculated from the mass loss. Subsequently, the samples were re-melted under salt-flux and compared with another set of samples which were re-melted without thermal pre-treatment. The results showed that thermal de-coating significantly promotes the coalescence of loose chips and briquettes compacted uniaxially, up to similar coalescences than initially uncoated aluminum samples. Thermally treating the MPT briquettes, which were more densely compacted, led to less de-coating, and subsequently lower coalescences. The analysis of re-melted material revealed that the coating residues did not significantly affect the composition, while the compaction prevented Mg loss for the uncoated materials. Graphical Abstract

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“…Research has also shown that compacting clean, dry aluminium swarf [27,28] into briquettes increases its recycling efficiency in a salt-free process. Furthermore, briquetting thin aluminium foil can prevent high-temperature-oxidation and the consequent entrapment of small beads by the salt residues [29]. The benefits of compaction could be explained by, depending on the process, the reduction of the surface area exposed to oxidation, the higher density allowing the scrap to sink into the melt, or the enhanced metal-metal contact.…”

Section: Introductionmentioning

confidence: 99%

Effects of Compaction and Thermal Pre-treatments on Generation of Dross and Off-Gases in Aluminium Recycling

Vallejo-Olivares,

Gertjegerdes,

Høgåsen

et al. 2023

J. Sustain. Metall.

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Organic coatings are a challenge for aluminium packaging recycling since they tend to increase the re-melting metal losses. A solution is de-coating the scrap via a thermal pre-treatment to burn-off the organics before re-melting. Due to logistic benefits, the scrap is often pressed into bales. This study evaluates the influence of compaction on the de-coating efficiency and off-gas emissions, and its consequences for dross formation and recycling metal yield. Loose chips and two types of briquettes, one loosely compacted by uniaxial pressure and the other compacted by moderated-pressure-torsion to higher densities, were heated to 550 °C while analysing the off-gas emissions using FTIR. The briquettes were subsequently re-melted into a molten heel. Re-melting coated scrap multiplied the % wt of dross by a factor of 2 or 3, depending on the compaction pre-treatment, compared to re-melting uncoated aluminium. The densest briquettes emitted less than half the CO2 and CO gases during de-coating and formed significantly more dross. Compaction to the lower densities showed no tangible effects. The effect of de-coating compacted materials or not was small (± 2% wt dross), which was attributed to carbonaceous residues remaining after the thermal treatment. In conclusion, high compactions by torsion limit the de-coating reactions, which depend on factors such as temperature and gas transport. A complete removal of the organic residues is critical for a more sustainable recycling with less dross generated. Graphical Abstract

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Compaction of Aluminium Foil and Its Effect on Oxidation and Recycling Yield

Cited by 5 publications

References 18 publications

Solid Salt Fluxes for Molten Aluminum Processing—A Review

Solid Salt Fluxes for Molten Aluminum Processing—A Review

Thermal De-coating Pre-treatment for Loose or Compacted Aluminum Scrap and Consequences for Salt-Flux Recycling

Effects of Compaction and Thermal Pre-treatments on Generation of Dross and Off-Gases in Aluminium Recycling

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