The Chemical Composition of Post-Consumer Aluminium Scrap – A Challenge in Aluminium Recycling

The Recycled Aluminum Dilemma: Mastering Chemical Composition for High-Integrity Die Casting

This technical summary is based on the academic paper "The Chemical Composition of Post-Consumer Aluminium Scrap – A Challenge in Aluminium Recycling" by Ciprian Bulei, Imre Kiss, and Mihai–Paul Todor, published in Acta Polytechnica Hungarica (2023).

Keywords

• Primary Keyword: Aluminium Recycling
• Secondary Keywords: Post-Consumer Aluminium Scrap, Chemical Composition, Secondary Aluminium, HPDC, Alloy Quality, Re-melting

Executive Summary

• The Challenge: The inconsistent and often contaminated chemical composition of post-consumer aluminium scrap presents a major challenge for producing high-quality, specification-compliant alloys for casting.
• The Method: The researchers conducted laboratory experiments involving the re-melting of different post-consumer aluminium scrap sources—beverage cans, castings, and electric cables—to analyze the resulting chemical composition.
• The Key Breakthrough: The study quantifies the significant variation in key alloying elements (like Mg, Si, Fe, Cu, Mn) and impurities across different scrap streams, highlighting the direct link between scrap source and final metal quality.
• The Bottom Line: Rigorous sorting, pre-treatment, and sourcing of post-consumer scrap are non-negotiable for controlling the chemical composition of secondary aluminium and ensuring the mechanical integrity of final cast products.

The Challenge: Why This Research Matters for HPDC Professionals

Aluminium is a cornerstone of modern manufacturing, prized for its light weight, strength, and corrosion resistance. Its infinite recyclability makes it a champion of the circular economy, offering massive energy savings (up to 95%) compared to primary production. For the High Pressure Die Casting (HPDC) industry, this presents a huge opportunity to reduce costs and improve environmental credentials by using secondary (recycled) aluminium.

However, this opportunity comes with a critical challenge. Unlike primary aluminium with its tightly controlled purity, post-consumer scrap is a mixed bag. It's a mixture of different alloys, and often, different metals entirely. Scrap from packaging, automotive parts, construction, and electronics all enters the recycling stream with unique chemical fingerprints. For an HPDC professional who relies on precise alloy specifications to prevent defects like hot tearing, ensure pressure tightness, and meet mechanical property targets, this variability is a significant operational risk. This research tackles this exact problem by investigating how the source of scrap directly impacts the chemical makeup of the final recycled metal.

The Approach: Unpacking the Methodology

The study provides a clear overview of the secondary aluminium production process, which was replicated in their laboratory experiments. The methodology focuses on understanding the transformation of raw scrap into usable ingots.

Method 1: Scrap Sourcing and Categorization
The researchers sourced distinct categories of post-consumer aluminium scrap to represent common industrial feedstocks. The primary types considered were:
- Used beverage cans
- Collected castings (e.g., car rims, engine blocks)
- Aluminium from electric cables

This separation is crucial because each source corresponds to different original alloys and potential contaminants.

Method 2: The Recycling Process Stream
The experiments followed the fundamental steps of industrial aluminium recycling:
1. Preparation (Pre-treatment): This initial stage involves sorting the scrap, preparing it dimensionally (e.g., shredding, baling), and removing impurities.
2. Elaboration (Melting and Refining): The sorted scrap is melted in a furnace. This is the core of the recycling process. Subsequent steps can include refining to remove dissolved gases and non-metallic inclusions, and alloying to adjust the chemical composition to meet specific standards.
3. Casting: The molten, refined metal is cast into ingots, which then become the raw material for manufacturing new products. The chemical composition of these final ingots was the primary object of analysis.

The Breakthrough: Key Findings & Data

The research provides hard data that quantifies the "chemical challenge" of using different scrap sources. The analysis of the re-melted ingots revealed distinct chemical profiles for each type of scrap.

Finding 1: Beverage Cans and Castings are Rich in Alloying Elements

Post-consumer beverage cans and automotive castings are major sources for secondary aluminium, but they introduce significant levels of alloying elements.
- Recycled Cans (Table 1): The resulting metal contained significant amounts of Magnesium (Mg: 0.402%), Iron (Fe: 0.567%), Silicon (Si: 0.281%), Manganese (Mn: 0.284%), and Copper (Cu: 0.130%). The presence of Lead (Pb: 0.337%) is also notable.
- Recycled Castings (Table 2): This stream produced a melt with even higher concentrations of key elements, particularly Iron (Fe: 1.65%), Magnesium (Mg: 0.739%), Manganese (Mn: 0.725%), and Lead (Pb: 0.980%). This composition is typical for casting alloys but requires careful management.

Finding 2: Electrical Cable Scrap is a Source of High-Purity Aluminium

In stark contrast to packaging and casting scrap, aluminium recovered from electric cables is exceptionally pure.
- Recycled Wires (Table 3): The analysis showed a very high aluminium content (Al: 99.55%). The levels of impurities and alloying elements were dramatically lower across the board, for example, Iron (Fe: 0.125%), Silicon (Si: 0.0881%), and Magnesium (Mg: 0.135%). This makes it a valuable resource for diluting less pure melts or for producing high-purity alloys.

Practical Implications for R&D and Operations

• For Process Engineers: This study underscores that not all "recycled aluminium" is the same. The high iron content (1.65%) from casting scrap, as shown in Table 2, can increase the risk of sludge formation and die soldering in HPDC. Understanding the scrap source of your ingot supply is critical for anticipating melt behavior and adjusting process parameters like shot speed and die temperature.
• For Quality Control Teams: The data in Tables 1, 2, and 3 provide a clear baseline for the expected range of elements from different scrap types. This knowledge can inform incoming material inspection protocols. For instance, an unusually high Pb or Zn content in a batch intended for a RoHS-compliant application could be traced back to the scrap source, preventing costly quality escapes.
• For Procurement and Sourcing Specialists: The chemical differences highlight the importance of strategic sourcing. While casting scrap is plentiful, its composition may limit its use to certain casting alloys. High-purity cable scrap, though less common, is a premium product that can be blended to upgrade lower-quality melts, offering a path to producing a wider range of alloys from recycled materials.

Paper Details

The Chemical Composition of Post-Consumer Aluminium Scrap – A Challenge in Aluminium Recycling

1. Overview:

• Title: The Chemical Composition of Post-Consumer Aluminium Scrap – A Challenge in Aluminium Recycling
• Author: Ciprian Bulei, Imre Kiss, Mihai–Paul Todor
• Year of publication: 2023
• Journal/academic society of publication: Acta Polytechnica Hungarica (Vol. 20, No. 9)
• Keywords: aluminium recycling; post-consumer aluminium scrap; re-melting; chemical composition

2. Abstract:

Aluminium is one of the most recyclable materials, as it can be recycled over and over again, and is one of few materials that keeps its properties after recycling. It can be re-melted and used again and again in new products, making it an environmentally friendly metal and a sustainable material. This makes aluminium an excellent material to meet the needs and challenges of different products. Also, aluminium recycling offers advantages in terms of environmental and economic benefits. Therefore, more aluminium must be collected, sorted, and returned into the economy as new products. Aluminium recycling is the process by which various scrap aluminium can reuse in products after its initial production and involves simply re-melting these scraps. This work provides an overview of the basic aluminium recycling process, using postconsumer scrap in the melting process in few laboratory experiments. Typically, postconsumer aluminium scrap is a mixture of alloys and sometimes even a mixture of metals, the main sources for aluminium scrap being the packaging, technology, construction, and the transport industry. In our experiments, different aluminium scrap sources were considered: mixed packaging aluminium scrap and used beverage can scrap, aluminium from electric cables and aluminium from collected castings. Having in view that the chemical composition is the main challenge in aluminium recycling, mass balance of main aluminium alloying elements is performed. This research provides an overview of the aluminium recycling process, from the scrap upgrading to the melting process.

3. Introduction:

Aluminium has become one of the most important structural materials, being the most widely used non-ferrous metal. Its use has seen continuous development across various industries, including aerospace, transport, and construction, where its properties of durability and strength are vital. The widespread use of aluminium and its alloys in automobiles, construction, packaging, and electricity has led to a significant accumulation of waste. This has given rise to the industry of secondary aluminium, or recycling. Recycling aluminium is of great importance due to its economic and environmental benefits, as it offers a lower-weight alternative to steel and fits well within a circular economy. The process saves up to 95% of the initial energy needed for primary production. Given its versatility and value, the aluminium industry has a strong interest in promoting recycling as part of its industrial strategy.

4. Summary of the study:

Background of the research topic:

The research is set against the backdrop of aluminium's status as a key industrial material and the growing importance of sustainability and circular economy principles. The material's inherent recyclability without loss of properties, combined with the significant energy and resource savings of recycling over primary production, makes secondary aluminium a critical resource. However, the value and usability of this resource are directly tied to its quality, which is primarily determined by its chemical composition.

Status of previous research:

The paper builds upon a body of existing work [1-13] that establishes the principles of waste management, the benefits of aluminium recycling, and the general process flow. It acknowledges the distinction between "new scrap" (from manufacturing, with known composition) and "old scrap" (post-consumer, with variable and contaminated composition). The challenge of managing the chemical composition of "old scrap" is a well-recognized issue in the field.

Purpose of the study:

The study aims to provide a practical overview of the aluminium recycling process and to experimentally demonstrate the primary challenge within it: managing the chemical composition. By analyzing and comparing the results of re-melting different, common types of post-consumer scrap, the research seeks to perform a mass balance of the main alloying elements and highlight how the scrap source dictates the quality and potential application of the recycled material.

Core study:

The core of the study involved laboratory experiments where three distinct types of post-consumer aluminium scrap were processed: (1) used beverage cans, (2) collected castings (e.g., from automotive parts), and (3) aluminium from electric cables. Each scrap type was melted down, and the resulting metal was cast into ingots. The chemical composition of these ingots was then analyzed to determine the levels of aluminium, primary alloying elements (Mg, Si, Cu, Mn, Zn), and common impurities (Fe, Pb, Sn).

5. Research Methodology

Research Design:

The research employed a comparative experimental design. Different categories of post-consumer aluminium scrap were selected as independent variables. The dependent variable was the chemical composition of the aluminium ingots produced after the re-melting process. The study was designed to simulate the basic industrial recycling stream in a controlled laboratory setting.

Data Collection and Analysis Methods:

Data was collected by performing chemical analysis on the cast ingots produced from each scrap type. The results of this analysis were presented in tabular format (Tables 1, 2, and 3), detailing the percentage by weight of various chemical elements. The analysis involved comparing these compositions to understand the mass balance of alloying elements and impurities contributed by each scrap source.

Research Topics and Scope:

The research topic is the chemical composition of post-consumer aluminium scrap as a challenge in the recycling process. The scope is focused on the re-melting stage and covers three common sources of scrap: beverage cans, castings, and electric wires. The study provides an overview from scrap upgrading to the melting process, with a specific focus on the resulting chemical makeup of the secondary metal.

6. Key Results:

Key Results:

• The chemical composition of recycled aluminium is highly dependent on its original source.
• Scrap from beverage cans (Table 1) yields an alloy with significant levels of Mg (0.402%), Fe (0.567%), and Mn (0.284%).
• Scrap from castings (Table 2) results in a secondary metal with high concentrations of Fe (1.65%), Mg (0.739%), Mn (0.725%), and Pb (0.980%), characteristic of casting alloys.
• Scrap from electric cables (Table 3) produces very high purity aluminium (99.55% Al) with low levels of all other elements, making it a valuable material for upgrading other melts.
• Impurities such as iron (Fe) and lead (Pb) are present in significant quantities in can and casting scrap, which can negatively affect the mechanical properties of new products if not properly managed.

Figure Name List:

• Figure 1: The aluminium life cycle
• Figure 2: Aluminium waste in the production phase respectively at the end of a product's life (after consumption) – example for the beverage cans
• Figure 3: The stream of aluminium waste to recycling into new products
• Figure 4: Re-melting the aluminium scrap
• Figure 5: Aluminium scraps melting process and cast ingots
• Figure 6: Aluminium scraps: beverage cans, castings and electric wires
• Figure 7: Aluminium scraps: melted aluminium and cast aluminium ingots

7. Conclusion:

All aluminium products can be recycled. Due to its high intrinsic value and the ability to be recycled almost without loss of quality, there is a strong incentive to recover and recycle aluminium products. The recycling process, however, faces the significant challenge of managing chemical composition, as recycled aluminium contains impurities and alloying elements that are difficult to manage. The quality of the scrap is directly related to the quality of the final alloy. During multiple recycling loops, more alloying elements are introduced into the metal cycle, an effect that is beneficial for producing casting alloys. The market exploitation of aluminium waste is economically viable and provides substantial environmental benefits. The future of sustainable manufacturing will rely heavily on using recycled aluminium from various sources, making the understanding and control of its chemical composition paramount for all industries that use it.

8. References:

• [1] D. Raabe, D. Ponge, P. J. Uggowitzer, M. Roscher, M. Paolantonio, C. Liu, H. Antrekowitsch, E. Kozeschnik, D. Seidmann, B. Gault, F. De Geuser, A. Deschamps, C. Hutchinson, C. Liu, Z. Li, P. Prangnell, J. Robson, P. Shanthraj, S. Vakili, C. Sinclair, L. Bourgeois, S. Pogatscher, Making sustainable aluminum by recycling scrap: The science of “dirty” alloys, Progress in Materials Science, 128, (2022) https://doi.org/10.1016/j.pmatsci.2022.100947
• [2] S. Capuzzi, G. Timelli, Preparation and melting of scrap in aluminum recycling: A review. Metals (Basel) (2018) 8:249, https://doi.org/10.3390/met8040249
• [3] A. T. Tabereaux, R. D. Peterson, Chapter 2.5 – Aluminum production, treatise on process metallurgy, Elsevier, 2014, 839-917, https://doi.org/10.1016/B978–0–08–096988–6.00023–7
• [4] P.de Schrynmakers, Life cycle thinking in the aluminium industry. The International Journal of Life Cycle Assessment, 14, 2-5 (2009) https://doi.org/10.1007/s11367-009-0072-x
• [5] G. Olivieri, A. Romani, P. Neri, Environmental and economic analysis of aluminium recycling through life cycle assessment, International Journal of Sustainable Development & World Ecology, 13:4, (2006) 269-276, https://doi:10.1080/13504500609469678
• [6] M. Niero, S. I. Olsen, Circular economy: To be or not to be in a closed product loop? A Life Cycle Assessment of aluminium cans with inclusion of alloying elements, Resources, Conservation and Recycling, 114, (2016) 18-31, https://doi.org/10.1016/j.resconrec.2016.06.023
• [7] G. Gaustad, E. Olivetti, R. Kirchain, Improving aluminum recycling: A survey of sorting and impurity removal technologies. Resources, Conservation and Recycling, 58, (2012) 79-87, https://doi.org/10.1016/j.resconrec.2011.10.010
• [8] G. Gaustad, E. Olivetti, R. Kirchain, Improving aluminum recycling: A survey of sorting and impurity removal technologies, Resources, Conservation and Recycling, 58, (2012) 79-87, https://doi.org/10.1016/j.resconrec.2011.10.010
• [9] S. K. Das, Emerging trends in aluminum recycling: Reasons and responses. Light Metals, 4, (2006) 911-916
• [10] J. R. Duflou, A. Erman Tekkaya, M. Haase, T. Welo, K. Vanmeensel, K. Kellens, W. Dewulf, D. Paraskevas, Environmental assessment of solid state recycling routes for aluminium alloys: Can solid state processes significantly reduce the environmental impact of aluminium recycling?, CIRP Annals, 64(1), (2015) 37-40, https://doi.org/10.1016/j.cirp.2015.04.051
• [11] V. K. Soo, J. Peeters, D. Paraskevas, P. Compston, M. Doolan, J. R. Duflou, Sustainable aluminium recycling of end-of-life products: A joining techniques perspective, Journal of Cleaner Production, 178 (2018) 119-132, https://doi.org/10.1016/j.jclepro.2017.12.235
• [12] S. Eggen, K. Sandaunet, L. Kolbeinsen, A. Kvithyld, Recycling of aluminium from mixed household waste. Light Metals (2020) 1091-1100, https://doi.org/10.1007/978–3–030-36408-3_148
• [13] S. Shamsudin, M. A. Lajis, Z. W. Zhong, Evolutionary in solid state recycling techniques of aluminium: a review. Procedia CIRP, 40, (2016) 256-261, https://doi.org/10.1016/j.procir.2016.01.117
• [14] C. Bulei, M. P. Todor, T. Heput, I. Kiss (2018) Recovering aluminium for recycling in reusable backyard foundry that melts aluminium cans. In IOP Conference Series: Materials Science and Engineering, 416(1), https://doi:10.1088/1757–899X/416/1/012099
• [15] C. Bulei, M. P. Todor, I. Kiss (2018) Metal matrix composites processing techniques using recycled aluminium alloy. In IOP Conference Series: Materials Science and Engineering, 393(1), https://doi:10.1088/1757-899X/393/1/012089
• [16] C. Bulei, M. P. Todor, I. Kiss, V. Alexa (2019) Aluminium matrix composites: Processing of matrix from re-melted aluminium wastes in micro-melting station. In IOP Conference Series: Materials Science and Engineering, 477(1), https://doi:10.1088/1757–899X/477/1/012049
• [17] C Bulei, I Kiss, V Alexa, Development of metal matrix composites using recycled secondary raw materials from aluminium wastes, Materials Today: Proceedings, 45(5), 2021, pp. 4143-4149, https://doi.org/10.1016/j.matpr.2020.11.926
• [18] U. M. J. Boin, M Bertram, Melting standardized aluminum scrap: A mass balance model for Europe. Jom, 57(8), (2005) 26-33

Expert Q&A: Your Top Questions Answered

Q1: Why were beverage cans, castings, and electric wires chosen specifically for this study?

A1: These three sources were chosen because they represent the wide spectrum of post-consumer aluminium scrap quality. Beverage cans are a high-volume, relatively consistent source from packaging. Castings represent the large and complex scrap stream from the automotive and transport industries. Electric wires are a source of very high-purity aluminium. By analyzing these distinct categories, the study effectively demonstrates the full range of chemical variability that recyclers and manufacturers must manage.

Q2: The paper mentions iron (Fe) as an impurity. Why is it such a concern in aluminium alloys for casting?

A2: The paper classifies iron as an impurity that "reacts chemically, forming various compounds, easily fusible." In practical terms for HPDC, high iron content promotes the formation of needle-like β-phase (AlFeSi) intermetallics. These brittle phases reduce ductility and fracture toughness in the final casting. They also contribute to sludge formation in holding furnaces and can increase the tendency for the molten alloy to solder to the die steel, leading to production downtime and reduced die life.

Q3: What is the difference between "pre-consumer" (new) and "post-consumer" (old) scrap, and why is it important?

A3: As defined in the paper, "pre-consumer" or "new scrap" is generated during manufacturing processes (e.g., off-cuts, shavings). Its chemical composition is known and consistent, making it easy to recycle directly. "Post-consumer" or "old scrap" comes from products that have completed their life cycle (e.g., a discarded window frame or engine block). This scrap is often a mix of alloys, contaminated with other materials, and has an unknown chemical history, making its recycling far more challenging.

Q4: Can the impurities in post-consumer scrap be removed during the re-melting process?

A4: The paper states that "To remove impure elements from a molten bath is impractical or inconvenient." While some refining processes can remove non-metallic inclusions and dissolved gases, removing metallic impurities like iron or copper is technologically complex and often not economically viable. Therefore, the primary strategy is not removal, but management through careful sorting of scrap, blending different scrap types (e.g., adding high-purity wire scrap to dilute a melt from castings), and directing the final melt to applications tolerant of its specific chemical composition.

Q5: According to the paper, what is the most significant opportunity to improve the quality of recycled aluminium?

A5: The paper concludes that the greatest opportunity lies in the "consumer packaging and the automotive sector." This implies that improving collection, and especially sorting, technologies for these high-volume streams is key. A "correct sorting process" is mentioned as a prerequisite for an efficient re-melting process. Better sorting would reduce cross-contamination and allow for the creation of higher-quality, more consistent scrap bales, which in turn would lead to more predictable and valuable secondary aluminium alloys.

Conclusion: Paving the Way for Higher Quality and Productivity

The challenge of inconsistent chemical composition is the single greatest hurdle in maximizing the value of post-consumer scrap in Aluminium Recycling. This research clearly demonstrates that the journey from a discarded can or car part to a high-quality ingot is governed by the chemistry of the scrap source. For the HPDC industry, this isn't just an academic exercise; it's a fundamental issue of process control, quality assurance, and profitability. By understanding the distinct chemical profiles of different scrap streams, manufacturers can make more informed sourcing decisions, anticipate processing challenges, and ultimately produce more reliable, high-performance components.

"At CASTMAN, we are committed to applying the latest industry research to help our customers achieve higher productivity and quality. If the challenges discussed in this paper align with your operational goals, contact our engineering team to explore how these principles can be implemented in your components."

Copyright Information

This content is a summary and analysis based on the paper "The Chemical Composition of Post-Consumer Aluminium Scrap – A Challenge in Aluminium Recycling" by "Ciprian Bulei, Imre Kiss, Mihai–Paul Todor".

Source: https://doi.org/10.1556/606.2023.00624

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