“Metals can be recycled indefinitely.” That marketing phrase of the metal producers sounds plausible, as we simply need to heat up and melt a bunch of scrap metal and cast and then roll or forge it into its new shape. With low-carbon heat, such perfect recycling could even largely eliminate GHG emissions from metal production, which is quite substantial at the moment. Steel production alone accounts for 7-9% of global energy-related GHG emissions . So we could solve the climate crisis (at least for the metal sector) and address resource concerns at the same time by saving metal ores!
Unfortunately, the real situation is not that simple and not perfect at all. A number of barriers exist for a perfectly closed metal cycle or the ideal of a ‘circular economy’:
- Recovery and sorting losses: Once discarded, many metals are currently not recovered as scrap from end-of-life (EoL) products such as mobile phones, laptops, motors, controllers, or batteries. Especially metals used in small quantities and concentrations only are often not recovered at all . Metals that are not extracted as scrap from old products cannot be recycled but end up in landfills instead. One main reason for this lack of recovery is that there is no business case for better scrap sorting. Metals from virgin resources (ores) are simply too cheap.
- Dissipative losses: Some metal applications, like their use in brake pads or as abrasive material, means that these metals get oxidized and dispersed during use with often no economic recovery option.
- Quality losses: Metals are often not used in pure form but as alloys (different metals are mixed in liquid phase) or in compounds (like printed circuit boards or computer chips). In product dismantling and shredding, different metals and alloys are mixed, which means that the metal scrap flows are not pure but contain also unwanted other metals, which usually lower the quality of the recycled metal and limits its application . For example, recycled steel is often contaminated with copper, and such steel can be used in long products (concrete reinforcement bars or steel girders) but not in flat products like sheet metal for cars. Even for ‘perfect’ recycling systems like aluminium drinking cans, there is contamination because the body and the cap are made of different alloys, which reduces the quality of the recycled material.
- Oxidation losses: Each remelting process leads to some metal getting oxidized and forming slag instead of secondary metal. For steel recycling, this loss rate is typically 4% but can be as high as 8% during one remelting step .
- Stock growth: if the in-use stock of a given metal expands globally, it has to be sourced from virgin resources, as any recycling only replaces stocks in the best case only allow for maintaining the stock. Current stock levels differ a lot among countries, and there will be a huge demand for material stock expansion also in the coming decades . Bringing developing regions to the same stock levels as currently enjoyed by the richer countries is a huge challenge climate-wise for the mass materials  and may lead to resource limitations for the minor and potentially critical materials.
The different loss rates together determine the fraction of all materials in EoL products that is potentially available as secondary (= recycled) material. They determine the ‘circularity’ of a material, which means: (a) how long does a unit of metal stay in useful applications (technical lifetime) and (b) how many product lifecycles does it participate in? The first indicator is called the longevity of a metal, the second one its circularity .
A recent study by Helbig et al.  reports the average technical lifetime of 18 metals (Fig. 1) and finds that many specialty metals such as cobalt (Co), tantalum (Ta), tungsten (W), zinc (Zn), or tin (Sn) have lifetimes of only 20 years or even well below that! That means, all the destruction of ecosystems, the climate impact and water pollution of mining and metal production is for a product that lasts less than 20 years on average, before it ends up in a slag pile or landfill! Chromium (Cr), silver (Ag), copper (Cu), and nickel (Ni) show average lifetimes of between 30 and 60 years, and only aluminium (Al) and iron/steel (Fe) reach lifetimes of 100 years and beyond. Still, given that the impacts on ecosystems and the climate, in particular, will last for much longer than 100 years, there is no good relation between the benefit side and the impact side of our metal use at all.
Fig. 1. Dissipation-to-Extraction Ratio (DER), Dissipation-to-Final-Production Ratio (DFR), and average technical lifetime. Source: .
What to do? A closer look at the metal cycle parameters in  reveals that low collection rates (EoL products don’t end up in proper recycling facilities) and low scrap extraction rates (metals are not recovered as scrap or end up in the scrap bins for other main metals) are the main reasons for that short lifetime.
In another just published study , Stefanie Klose takes a closer look at copper with a base lifetime of just 45-50 years. She shows that strategies addressing single parameters, like increasing the recovery rate or product lifetime, can all lead to higher average lifetimes of up to 60 years, a 28% increase max. from the base value. More substantial increases, however, can only be achieved if different strategies to increase the lifetime and thus the overall usability of the produced copper are combined: Longer product lifetime AND higher recovery rate. This applies to electronic goods, in particular, which are in the focus of this study. Combined measures can lead to an increase of the copper lifetime of 85-90 years, which is almost twice the current value.
Fig. 2. Different resource efficiency scenarios affect circularity (no. of product life cycles for a unit of copper from copper ore) and longevity (average technosphere lifetime) in different ways. The red dot shows the BAU scenario, the blue dots the moderate and ambitious single resource efficiency strategies, and the green and the yellow dots are combinations of these. Source and strategy details .
This is an encouraging result. Copper is relatively easy to recover and recycle, so that there is a high change that better standards for product repairability, ease of dismantling and better scrap sorting will lead to substantial lifetime increase and thus will lower the demand for copper ore and related environmental impacts. Detailed cost assessments can show what incentives or regulations are needed for businesses to pick up the different strategies that increase the lifetime of copper.
Still, a 90 years lifetime means that even when copper stocks don’t grow anymore, the total stock needs to be replaced more than once in each century. This is unsustainable given the declining ore grades and rising energy, water, and land use of copper ore mining [10, 11]. To decouple copper use from the negative impacts of its production even more, even stricter measures than the ones studied here will be needed, potentially including the mining of slag piles or landfills for copper or the phase-out of copper from low lifetime or dissipative applications.
The analyses presented here show what is currently possible in dynamic material flow analysis with the data we have available and what indicators we can derive from our models to characterizes the current ‘circularity’ of our metal use and how it can be improved in the future. Both studies make use of the so-called MaTrace model for tracing material flows through the technosphere , which is an application of dynamic material flow analysis.
References. Access date: Feb. 7, 2021.
 Worldsteel Association: SUSTAINABLE STEEL Indicators 2018. https://www.worldsteel.org/en/dam/jcr:ee94a0b6-48d7-4110-b16e-e78db2769d8c/Sustainability%2520Indicators%25202018.pdf
 What Do We Know About Metal Recycling Rates? By Graedel et al. (2011), DOI 10.1111/j.1530-9290.2011.00342.x
 Circular Economy: Theoretical Benchmark or Perpetual Motion Machine?, By Cullen (2017), DOI 10.1111/jiec.12599
 Regional distribution and losses of end-of-life steel throughout multiple product life cycles—Insights from the global multiregional MaTrace model, by Pauliuk et al. (2017), DOI 10.1016/j.resconrec.2016.09.029
 Carbon emissions of infrastructure development. By Müller et al. (2013), DOI 10.1021/es402618m
 Global Metal Use Targets in Line with Climate Goals, by Watari et al. (2920), DOI 10.1021/acs.est.0c02471
 Resource duration as a managerial indicator for Circular Economy performance, by Franklin-Johnson et al. (2016), DOI 10.1016/j.jclepro.2016.05.023
 Resources, Conservation & Recycling: Quantitative assessment of dissipative losses of 18 metals, by Helbig et al. (2020), DOI 10.1016/j.resconrec.2019.104537
 Quantifying longevity and circularity of copper for different resource efficiency policies at the material and product levels, by Klose and Pauliuk (2021), DOI 10.1111/jiec.13092 https://onlinelibrary.wiley.com/doi/full/10.1111/jiec.13092
 Modelling future copper ore grade decline based on a detailed assessment of copper resources and mining, by Northey et al. (2014), DOI 10.1016/j.resconrec.2013.10.005
 A PROJECTION OF FUTURE ENERGY AND GREENHOUSE GAS EMISSIONS INTENSITY FROM COPPER MINING, by Mudd et al. (2013).
 MaTrace: Tracing the Fate of Materials over Time and Across Products in Open-Loop Recycling, by Nakamura et al. (2014), DOI 10.1021/es500820h