Dross Formation Mechanisms of Thermally Pre-Treated Used Beverage Can Scrap Bales with Different Density

Steglich, Jan; Dittrich, R.; Rombach, G.; Rosefort, Marcel; Friedrich, Bernd; Pichat, A.

doi:10.1007/978-3-319-51541-0_133

Cited by 8 publications

(4 citation statements)

References 7 publications

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“…However, the coalescence was lower for the de-coated MPT briquettes. The reason may be that the MPT briquettes are so tightly compacted that oxygen cannot penetrate into the briquette, partly inhibiting the de-coating, as previously suggested by Steglich [32], and consequently, the resulting residues limit the ability of chips to coalesce together as also suggested by Capuzzi [14]. These results are consistent with the previous section.…”

Section: Re-melting Coalescencesupporting

confidence: 90%

“…Whether the scrap is loose or compacted during the thermal treatment may affect the removal of organics as it may alter scrap heat transfer and exposure to oxygen. Steglich [8] thermally treated bales of used beverage cans (UBCs) and foils and observed a correlation between the thermal conductivity of the bales and their density and porosity. According to Wells [9], the heat transferred through bales of UBCs is much lower than through a block of solid aluminum.…”

Section: Introductionmentioning

confidence: 99%

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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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Section: Re-melting Coalescencesupporting

confidence: 90%

Section: Introductionmentioning

confidence: 99%

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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“…The pyrolysis of a similar coating leads to the formation of adhering carbon coating char on the can sheets. 7 Dross Formation D and Can Alloy Oxidation D is attributed to the oxidation of metals and inclusion of liquid aluminum alloys in corresponding oxides. The oxidized metal cannot be recovered in the current industrial processes and is defined as metal loss, whereas the trapped alloy can be recovered by dross processing.…”

Section: Literature Review Can Coating Removal and Residuementioning

confidence: 99%

Dross Formation in Aluminum Melts During the Charging of Beverage Can Scrap Bales with Different Densities Using Various Thermal Pretreatments

Steglich

Friedrich

Rosefort

2020

JOM

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“…To secure a complete removal of the organics during de-coating, the process parameters (temperature, atmosphere, duration) must be carefully controlled. Studies showed that treatments under inert gas-atmospheres and low temperatures can leave pyrolysis residues [26] which lead to re-melting losses by increasing the amount of dross generated in salt-free processes [25] or by lowering the coalescence of aluminium droplets and thus increasing the amount of aluminium entrapped in the salt slag residues when recycling in rotary furnaces [19]. On the other hand, using higher temperatures and O 2 -rich atmospheres increases the risk of oxidizing the scrap.…”

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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Dross Formation Mechanisms of Thermally Pre-Treated Used Beverage Can Scrap Bales with Different Density

Cited by 8 publications

References 7 publications

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

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

Dross Formation in Aluminum Melts During the Charging of Beverage Can Scrap Bales with Different Densities Using Various Thermal Pretreatments

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

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