Mapping Global Steel Scrap Flows (2023 PDF)
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Universidade Federal de Pernambuco, Universidade Federal do Rio de Janeiro
2023
Wenqiu Cai, Yong Geng, Meng Li, Ziyan Gao, Wendong Wei
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Summary
This research maps the global flows of steel scraps and the embodied alloy elements (AEs) over the period of 2000-2021, using trade-linked material flow analysis and social network analysis. The findings highlight the increasing global steel scrap trade, with several core countries (USA, Germany, and Turkey) leading the network. The study emphasizes the transfer of critical metals, such as chromium, nickel, and manganese, across borders, urging efforts to improve resource efficiency.
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LETTER OPEN ACCESS You may also like - Enhancing the Mechanical Characteristics Mapping the global flows of steel scrap...
LETTER OPEN ACCESS You may also like - Enhancing the Mechanical Characteristics Mapping the global flows of steel scraps: an alloy of the Traditional Concrete with the Steel Scrap elements recovery perspective N Venugopal, L Emmanual, Prashant Sunagar et al. - Melt refining and purification processes in To cite this article: Wenqiu Cai et al 2023 Environ. Res. Lett. 18 094048 Al alloys: a comprehensive study Jianxin Wu, Faramarz Djavanroodi, Ceren Gode et al. - Refining effect of TiAl intermetallic compounds prepared by hydrogen plasma View the article online for updates and enhancements. arc melting from scraps of Ti–Al mixture Do Sung Lee, Jung-Min Oh, Jun-Ho Seo et al. This content was downloaded from IP address 190.97.251.72 on 05/10/2024 at 02:45 Environ. Res. Lett. 18 (2023) 094048 https://doi.org/10.1088/1748-9326/acf2ad LETTER Mapping the global flows of steel scraps: an alloy elements OPEN ACCESS recovery perspective RECEIVED 29 May 2023 Wenqiu Cai1, Yong Geng1,2,∗, Meng Li2, Ziyan Gao1 and Wendong Wei2,∗ REVISED 1 12 August 2023 School of International and Public Affairs, Shanghai Jiao Tong University, Shanghai 200030, People’s Republic of China 2 School of Environmental Science and Engineering, Shanghai Jiao Tong University, Shanghai 200240, People’s Republic of China ACCEPTED FOR PUBLICATION ∗ 22 August 2023 Authors to whom any correspondence should be addressed. PUBLISHED E-mail: [email protected] and [email protected] 7 September 2023 Keywords: steel scraps, social network analysis, alloy elements, material flow analysis, governance, resource management Original content from Supplementary material for this article is available online this work may be used under the terms of the Creative Commons Attribution 4.0 licence. Abstract Any further distribution Recycling steel scraps by the use of electric arc furnace is one of the most promising approaches for of this work must maintain attribution to the steel industry to achieve net-zero emissions. Due to the uneven distribution of global steel the author(s) and the title of the work, journal scraps, many countries are actively involving in the global steel scraps trade. Steel scraps contain a citation and DOI. range of critical elements, which may be transferred across borders through international trade of steel scraps. However, existing studies have paid little attention to the global flows of steel scraps and its embodied alloy elements (AEs). This study maps the journey of global steel scraps and the embodied AEs for the period of 2000–2021 for the first time by employing trade-linked material flow analysis and social network analysis. The results indicate that the global steel scraps trade had increased during the study period, with a few core countries (such as USA, Germany, and Turkey) leading the global steel scraps network. Also, critical metals had been transferred across borders in the form of AEs through the trade of steel scraps, especially from global north countries to global south countries. The largest AE flows include Chromium (Cr), nickel (Ni), manganese (Mn) and molybdenum (Mo) flows. Other AE flows, such as cobalt (Co), vanadium (V), and niobium (Nb) flows, were less, but with high values or being regarded scarce. From a global perspective, steel scraps trade and recycling can contribute to the decarbonization efforts of the global steel industry and address resource shortages in some countries. Therefore, it is urgent to promote the overall resource efficiency of steel scraps and the embodied AEs by various efforts. 1. Introduction requires an energy input of only 8.7%–25.0% of that in the primary steel production route (Harvey 2021). The Paris Climate Agreement established an ambi- As such, the carbon footprint per ton of recycled steel tious climate target of achieving net-zero by 2050 (van is only 10%–20% of that of the primary steel (Fan and Vuuren et al 2018, van Soest et al 2021). As the largest Friedmann 2021). However, only 40.3% of the global industrial emission source (Li and Hanaoka 2022), steel production comes from steel scraps (Wang et al steel and iron industry alone accounted for 25% of the 2021a). The availability of steel scraps is substantially global direct industrial carbon emissions (Ren et al limited by the historical production and the life spans 2021), implying an urgent need to decarbonize this of various steel-containing products (Pauliuk et al sector (Li et al 2019). As the most promising mater- 2013b), especially in countries with low industrializ- ial to replace virgin iron ore production, steel scraps ation levels (Pauliuk et al 2013a). Several countries can be recycled repeatedly without losing its prop- rely heavily on importing steel scraps to meet their erties so that energy consumption and carbon emis- domestic demand (Neşer et al 2008). But these coun- sions can be reduced (International Energy Agency tries are facing a risk of supply chain disruptions, 2020). Recycling steel scraps in electric arc furnaces which may be induced by geopolitical conflicts, price © 2023 The Author(s). Published by IOP Publishing Ltd Environ. Res. Lett. 18 (2023) 094048 W Cai et al volatility, and a lack of collection system (Liu and theory (Wasserman and Faust 1994). It is an effect- Müller 2013). ive method to identify patterns of relations among Practically, steel is not always used in its pure components within a system (An et al 2014), and form, but is frequently alloyed with other elements can objectively assess a country’s market dominance in order to enhance its performance (Ohno et al through metrics such as trade volume, number of 2015, Tan et al 2021), such as increased strength, trade relations, and trade intensity (Liu et al 2022, high corrosion resistance, light weight, longer life Zhou et al 2022). This method has been widely used spans, and better recyclability. For instance, zinc to study the characteristics of international trade (Zn), aluminum (Al), and tin (Sn) are added as networks for various commodities, such as metal coating elements to enhance the corrosion resist- resources (Ge et al 2016, Tokito et al 2016, Zhong ance of steel (Panasiuk et al 2022). Other alloy ele- et al 2018, Wang et al 2019, Shao et al 2021, Zheng ments (AEs) include manganese (Mn), chromium et al 2022, Gao et al 2022a), energy products (Du et al (Cr), nickel (Ni), molybdenum (Mo), vanadium(V), 2017, Chen et al 2018, Wang et al 2019) and solid etc (Nakajima et al 2013). Functional recovery of steel waste (Wang et al 2020b, Ma et al 2021). However, scraps only occurs when AEs end up in the right although several scholars highlighted the importance place (Graedel et al 2011). However, it is difficult to of studying the trade patterns of steel scraps (Lee and remove such AEs from steel scraps, which may result Sohn 2015, Zhong et al 2018), little attention has been in the functional loss of AEs or steel contamination paid on the trade linkages between different countries (Nakamura et al 2012, Diener and Tillman 2015). A or regions from an AEs transfer perspective. typical example is that high-quality steel sheets from In summary, in order to address the above con- vehicles are downgraded into ordinary steel for con- cerns, this study investigates the global flows of steel struction purposes (Ohno et al 2014, Hertwich et al scraps and its embodied AEs by integrating trade- 2019). Although several scholars have investigated the linked MFA with social network analysis so that the criticality of embodied AE flows, their efforts mainly potential risks in the global steel scraps trade can focus on several AEs with higher concentrations in be identified. We expect to recognize the dilemma the steel scraps, such as Ni, Cr, Mn, and Mo (Daigo of embodied AEs in global steel scraps recycling so et al 2010, Nakajima et al 2013, Ohno et al 2016, 2017, that valuable insights can be obtained for preparing Nakamura et al 2017). A comprehensive evaluation appropriate resource management policies. covering all the critical elements embodied in steel scraps is still lacking, especially at the global level. 2. Methods and data Most of these AEs are critical metals for achieving the net-zero future. For example, Co and Ni play import- We measure the global trade flows of steel scraps ant roles in the transformation of energy systems. By and its embodied AEs between different countries by 2040, the global demand for these metals may be 19 applying a trade-linked MFA and then investigate the and 22 times higher than that in 2020 (International trade patterns of steel scraps and individual AEs by Energy Agency 2021). Some of them have higher eco- conducting social network analysis. The global steel nomic value, such as V and Nb (Tan et al 2021), which scraps trade network (GSSTN) includes more than deserve more attention. 200 countries and regions, and the temporal bound- Material flow analysis (MFA) is a mature method ary of this study is from 2000 to 2021. The investig- to systematically measure the flows and stocks of ated AEs include manganese (Mn), nickel (Ni), zinc one material within predefined spatial and temporal (Zn), stannum (Sn), plumbum (Pb), copper (Cu), boundaries (Brunner and Rechberger 2016). To date, aluminum (Al), chromium (Cr), cobalt (Co), vana- MFA has widely been used to track the metabolic dium (V), niobium (Nb), and molybdenum (Mo). evolution of critical metals during their entire life All the detailed explanations of data processing are cycles (Graedel et al 2004, Wang et al 2007, Cullen et al presented in the Supporting Information. 2012, Glöser et al 2013, Su et al 2023). Since metal ele- ments may cross national boundaries multiple times 2.1. Trade-linked MFA during production, fabrication and manufacturing The global anthropogenic iron & steel cycle usually stages (Liu and Müller 2013), several studies invest- includes primary production, fabrication and man- igate the material flows embodied in international ufacturing, final use, and waste management stages trade based on a trade-linked MFA framework (Sun (Zhong et al 2018). In this study, we focus on the et al 2017, 2019, Wang et al 2022, Gao et al 2022a). waste management stage. However, these studies typically investigate one single We trace all AE flows in AE metallic equivalents metal element from a life cycle perspective and rarely by compiling extensive data from various sources, focus on all the AEs contained in a specific steel including reported statistics, published literature and product. expert interviews. Bilateral trade data of steel scraps Social network analysis refers to the process of were obtained from the UN Comtrade database (UN investigating trade networks and relations between Comtrade 2023). Table S1 lists different steel scraps countries based on network science and the graph products covered in this study, along with their 2 Environ. Res. Lett. 18 (2023) 094048 W Cai et al Table 1. Indicators used in social network analysis. Indicator Explanation In-degree The in-degree of a node refers to the number of countries importing Degree steel scraps products from a specified country. Out-degree The out-degree of a node refers to the number of countries exporting steel scraps products to a specified country. In-strength In-strength refers to the imported trade volume of the edges connected Strength to a node. Out-strength Out-strength refers to the exported trade volume of the edges connected to a node. Betweenness centrality The betweenness centrality of one node refers to the number of these shortest paths that pass through this node. Modularity index The modularity index refers to the density of links inside communities. harmonized system (HS) codes, including seven types out-strength, betweenness centrality, and modularity of steel scraps products. We chose net weights (phys- indicators (table 1) (Jackson 2010, Liu et al 2016, ical quantity) of steel scraps and AE contents (%) to Jiang et al 2019, Ma et al 2021, Pacini et al 2021, Gao explore the associated AE flows. The contents of AEs et al 2022a). The associated calculation methods are are listed in table S2 of the supporting information. detailed in the supporting information. The amount of AE x embodied in the steel scraps trade is calculated by using equation (1), 2.3. Uncertainty analysis ∑n All AEs flows are calculated based on the actual Mx = Ap × Rpx (1) contents of such elements in different steel scraps p products under different HS codes (Wang et al where Mx represents the total mass of the AE x in the 2021b). The uncertainty of this study is mainly caused steel scraps; p represents each traded steel scraps com- by the AEs contents (Gao et al 2022b). Simplified modity and is presented by one HS code; n repres- ranges are determined to estimate the uncertainties ents the number of involved steel scraps types, with (Laner et al 2014). According to a previous study, the a maximum number of 7; Ap represents the mass of aggregate uncertainty for element concentration data each steel scraps commodity under p HS code, Rpx may be lower than 20% (Liu et al 2013). Relevant represents the content of each AE embodied in each studies on steel AEs present that such uncertainty involved steel scraps commodity under p HS code. ranges from 2% to 10% (Gao et al 2022b, Su et al 2023). Therefore, we assume the uncertainty ranges 2.2. Social network analysis of AEs contents directly collected from databases and Social network analysis is used to analyze the trade literature are at a low level (2%), while the uncer- network structure of global steel scraps and its tainty ranges derived from estimated parameters are embodied AEs. Gephi software is used to visualize assumed to be high (10%). The calculated results are this network so that bilateral trade relations for steel illustrated in figures S54 and S55 of the Supporting scraps can be presented, in which each node repres- Information. ents a country and each edge represents a bilateral relationship between two involved countries. This 3. Results network model is composed of a node-set (P) and an edge-set (Q), where P= {pi : i = 1,2,…,n} (Gao 3.1. Features of the GSSTN et al 2022a), n is the number of nodes, and Q= By considering the top 80% of the global steel scraps {qi : i = 1,2,…,m}, m is the number of edges. The trade volume during 2000–2021, we identified a total adjacency matrix of this network is expressed by of 44 key nodes within GSSTN (figures S1, S2 and equation (2), table S3). Figure 1 shows the trade patterns of key nodes within GSSTN from 2000 to 2021, in which the 0 ω1,2 · · · ω1,n top three exporters were the United Kingdom (153.89 ω2,1 0 · · · ω2,n Mt), Japan (143.31 Mt), the Russian Federation G = (P, Q) = ...... (2) .. 0. (131.46 Mt), while the top three importers were ωn,1 ωn,2 ··· 0 Turkey (344.75 Mt), Republic of Korea (139.26 Mt), Spain (113.73 Mt). During the study period, sev- where ωij represents the weight of the edge from node eral countries emerged as key players in the global m to node n. steel scraps trade, including the USA, Canada, and Several indicators are used to analyze the fea- Denmark, which are key nodes in the export trade tures of the GSSTN and the embodied AEs networks, network, while Pakistan and Viet Nam emerged as including in-degree and out-degree, in-strength and key nodes in the import trade network. In contrast, 3 Environ. Res. Lett. 18 (2023) 094048 W Cai et al Figure 1. Trade patterns of key nodes within GSSTN from 2000 to 2021. unit: kilotons (kt)]. Note: 1. Countries are ranked by the net import amount from left to right, with positive values indicating imports and negative values indicating exports. 2. The evolution of steel scraps trade volume among these key nodes is detailed in the Supporting Information figures S4–S47. 3. The red line represents the net-import of each key node. several other countries, such as Ukraine, Georgia, and those low and middle-income countries in Africa, China, gradually reduced their roles in the global steel South America, and Asia. However, being influenced scraps trade. by COVID-19, the number of participating coun- The global traded steel scraps amount experi- tries in GSSTN decreased significantly after 2020 enced a fluctuating upward trend, increasing from (figure S50). Also, different regions have different 51.25 Mt in 2000–103.62 Mt in 2021 (figure S49). trade patterns. The main export destinations of those Highly industrialized countries in Europe and North European countries include the Mediterranean and America were the main exporters of the steel scraps, Arabian countries, while the main export destinations with several European countries such as Germany, the of Asian countries include those East and Southeast Netherlands, France and Belgium ranking among the Asian countries. Moreover, the destinations for those top ten steel scraps exporters. After 2006, the USA American countries are relatively diversified, with dominated the global steel scraps export, increasing South American and Asian countries as the main des- from 14 181.67 kilotons (kt) in 2000 to 16 482.97 kt tinations. in 2021. Emerging economies, such as Turkey, China, The number of communities in GSSTN fluctu- and India, became the main importers of steel scraps. ated considerably between 2000 and 2021, ranging Particularly, Turkey has become the world’s largest from 5 to 10. Overall, the modularity of GSSTN importer of steel scraps, accounting for more than has remained high, with values between 0.32 and 14% of the global steel scraps trade annually (except 0.52 (figure S51), indicating a good quality of com- for 2009). Due to the implementation of Solid Waste munity division. However, a fluctuating decline in the Import Ban policy, China has significantly decreased modularity index can be observed during this period its steel scraps import since 2017. The total imported although it has become stabilized since 2018. This steel scraps reached a minimum value of 254.19 kt in phenomenon shows that the steel scraps trade has 2020, which is only 1.59% of its total import in 2009 become increasingly globalized in recent years, and (with a figure of 16 016.56 kt). the division of each community has become less signi- The global steel scraps flows are visualized in ficant. Also, GSSTN remained a hierarchical structure figure 2, indicating that the total trade volume has during the study period, which has been dominated significantly increased with more intensive trade by a few core countries. The community structure relations. New participants in GSSTN were mostly of GSSTN experienced a dynamic evolution trend 4 Environ. Res. Lett. 18 (2023) 094048 W Cai et al Figure 2. Global steel scraps trade network in 2000 (a), 2007 (b), 2014 (c), and 2021 (d). Note: 1. Each curve represents one steel scraps trade relation, flowing from an export country to an import country with a clockwise direction; 2. The size of each node represents the total trade volume of a country; 3. The width of each edge represents the trade flow between two trading partners; 4. Different colors represent different communities. Nodes within GSSTN are grouped by community detection, with nodes in the same community being more densely connected to each other than to the rest of the network. The community number represents the ranking of each community, with community 1 representing the community with the most trade relations, while community 10 representing the community with the least trade relations. 5. Since countries in communities 6–10 have significantly smaller trade volumes than those in the top five communities, we do not include trade relations within communities 6–10 in this figure. (figure S52). Specifically, the main communities in 3.2. Global flow patterns of AEs embodied in steel this GSSTN have shifted from the European com- scraps trade munity to the American-Asian communities after With the increasing steel scraps trade, the total 2007, in which Southeast Asian countries played a amount of each AE embodied in global steel scraps more important role. The community division of trade increased from 1076.12 kt in 2000 to 2413.25 this GSSTN was geographically clustered in its early kt in 2021 (figure 3(a)). In particular, a surge of stage, indicating that countries with shorter distances embodied AEs occurred in 2004. Typical AEs, such had closer trade relations. For example, the com- as V, Nb, and Ni, had grown faster than other AEs, munity with the most trade relations was mainly increasing by more than 1.5 times. Sn had the slow- composed of several European countries, such as est growth rate of 60.67%. The most embodied AEs Germany, the United Kingdom, and the Netherlands. include Cr (21 304.79 kt), Ni (8997.67 kt), and Mn Originally, these countries had more intensive steel (6759.82 kt) due to their universal and vital functions scraps trade relations. But later on, these countries in various types of steel products. These elements began to have more transactions with non-European together accounted for more than 80% of all the AEs countries. In addition, the globalization further made (figure 3(b)). Other key embodied AEs include Cu, several African countries, such as Mozambique and Mo, Zn, Sn, and Pb, with a total amount ranging Zambia, involved in the core communities. Several from 300 kt to 2500 kt. The amount of each of other traditional export countries, such as the United remaining AEs is below 210 kt. However, although the Kingdom, Germany, and the USA, have a high level contents of these AEs in the steel products are relat- of connectivity (high betweenness centrality) in this ively less, their market values are high due to their GSSTN, meaning that these countries have stronger scarcity and irreplaceability, such as Nb, Co, and V. resource control capabilities and are critical hub We compared the structure of embodied AEs countries in GSSTN. Similarly, major steel scraps within GSSTN (figure 4 and supporting information import countries, such as India and Turkey, gradually figure S53). International steel scraps flows may not increased their connectivity in GSSTN, demonstrat- necessarily result in significant losses/acquisitions of ing that they had diversified trade partners for steel embodied AEs. For example, although Ukraine was scraps. the third largest steel scraps exporter in 2000, its total 5 Environ. Res. Lett. 18 (2023) 094048 W Cai et al Figure 3. Trade amounts of AEs embodied in global steel scraps from 2000 to 2021. (a) Historical evolution of global exports of each alloy element embodied in steel scraps over 2000–2021 (unit: kt); (b) Shares of AEs embodied in steel scraps over 2000–2021. (c) Top ten countries in total exports of each alloy element embodied in steel scraps from 2000 to 2021 (unit: kt). (d) Top ten countries in total imports of each alloy element embodied in steel scraps from 2000 to 2021 (unit: kt). Figure 4. The amounts of alloy elements in key countries accounting for 80% of the global steel scraps exports and imports in 2000 (a), 2007 (b), 2014 (c), and 2021 (d) (unit: kt). AEs only ranked the 12th in the world. Similarly, In addition, regional disparities exist in terms of the Egypt was the 10th largest steel scraps importer in trade structure of AEs. Countries mainly involving in 2014, but only ranked the 22nd in terms of its embod- stainless steel scraps trade, such as Germany, Belgium, ied AEs. The trade of steel scraps resulted in a con- and India, had much higher Cr, Ni, and Mo contents siderable amount of embodied AEs (mainly Cr, Ni, embodied in their traded steel scraps. In contrast, Mn, and Mo) transferring from developed econom- countries mainly involved in cast iron scraps and steel ies to developing countries (figures 3(c) and (d)). ingots for remelting, such as Malaysia, Belarus, and 6 Environ. Res. Lett. 18 (2023) 094048 W Cai et al Figure 5. Trade networks of alloy elements embodied in steel scraps from 2000 to 2021 (unit: kt). Note: 1. Each curve represents the trade flow of each AE embodied in steel scraps. 2. The size of each node represents the total trade amount of a country. 3. The width of each edge represents the trade flow between two trading partners. 4. Different colors represent different communities. Nodes within GSSTN are grouped by community detection, with nodes in the same community being more densely connected to each other than to the rest of the network. The community number represents the ranking of each community, with Community 1 representing the community with the largest trade relations, while Community 10 representing the community with the least trade relations. Lebanon, contributed much less to the international USA, from Mexico to the USA, and from the USA flows of AEs. to China were always the top three trade flows, sev- The global flows of different AEs embodied in eral characteristics are observed. For example, India steel scraps trade are illustrated in figure 5. India, and the United Kingdom dominated the first com- Netherlands, Germany, and the United Kingdom have munity (the community with the most trade rela- higher betweenness centrality values for all the AEs, tions) in both embodied Ni and Nb networks. In con- indicating that these countries played a vital role in trast, American and Asian countries dominated the the flows of AEs embodied in global steel scraps trade. first community in the embodied V network, such as The value of modularity indicates the extent to which the Republic of Korea and Canada. Similarly, India, communities are divided in different embodied AE Spain, and the United Kingdom dominated the first trade patterns. Except for Sn (0.15) and V (0.16), community in the embodied Mo network. And, sev- other AEs have clear community divisions, with mod- eral European and Asian countries dominated the ularity values ranging from 0.46 to 0.58, indicating first community in the embodied Sn trade network. distinct trade centers within their respective network Finally, Spain, India, United Kingdom, and Thailand communities. In the embodied V, Ni, and Nb trade dominated the first community in the embodied Cr networks, although the flows from Canada to the trade network, while Germany, Finland, and Italy 7 Environ. Res. Lett. 18 (2023) 094048 W Cai et al dominated the second community (the community products. Additionally, since several core countries with the second largest trade relations). dominated this GSSTN, their policies on steel scraps trade can greatly influence the global steel scraps 4. Discussion trade structure. For instance, with the implementa- tion of Solid Waste Import Ban policy, China gradu- 4.1. Environmental challenges and potential risks ally reduced its core role in the global steel scraps in the global steel scraps trade trade (figure 2). Consequently, as China’s original The global distribution of steel scraps supply is cur- trade partner, Japan began to sell steel scraps to other rently uneven, with highly industrialized countries Asian countries, such as Viet Nam and Bangladesh. contributing significantly to the global market. These Moreover, our social network analysis results countries have more in-use steel stocks and can col- reflect that only a few countries have the most lect more steel scraps from their end-of-life products trade relations within GSSTN. Most countries tend (Pauliuk et al 2013a). Also, they sell their steel to keep their original trade partners. However, due scraps due to their stricter environmental regulations. to the clear emission reduction feature of recycled Although secondary steel production is less energy steel, now more countries have determined to sup- and emission intensive, these developed countries still port steel recycling within their territories and begun prefer to purchase steel products from other countries to restrict the export of their steel scraps, such as so that they can avoid such energy consumption and Argentina (Lee 2023), the United Arab Emirates corresponding emissions (De Sa and Korinek 2021). (Gerber Group 2022), and Kenya (The Scrap Metal In contrast, developing economies, such as Turkey, Council 2015). The EU has also restricted the China, and India, are still experiencing rapid industri- export of such steel scraps to non-OECD coun- alization and urbanization and have higher demands tries (European Commission 2021). Similarly, sev- for steel products. Compared with developed eco- eral countries have restricted the export of their nomies, these countries typically have lax envir- steel scraps by charging higher export taxes (Price onmental regulations and ineffective enforcement. and Nance 2009). For instance, the export tariff rate Therefore, international steel scraps trade may further on steel scraps is 40% in China (Recycling Today result in cross-border transfer of associated environ- 2017), while the export tariff on steel scraps is mental burdens (Schütz et al 2004, Wang et al 2021b). €290/ton in Russia if the exported amount exceeds For example, India imported a large amount of steel the official quota (International Information Group scraps during 2000–2021 (figures 1 and 2). However, 2022). These policy changes may disrupt current steel the waste recycling industry in India is poorly man- scraps supply chain. In particular, trade restrictions aged (Schoot Uiterkamp et al 2011, Rathore 2020). on steel scraps by those more developed countries The recycled steel from steel scraps by its formal sec- may lower production efficiency in emerging eco- tor accounted for only about 5% of the total recycled nomics, especially advanced developing countries, steel (Awasthi and Li 2017). This country is cur- since it is difficult for them to access cheap steel rently the second largest steel producer in the world scraps (Yamaguchi 2018). For example, several coun- (Dakua 2019), in which recycled steel accounted for tries (such as Turkey) heavily rely on importing more than 55% of the total steel production (The steel scraps to support their steel industry (Özdemir World Steel Association 2020). It is expected that et al 2018). These countries may suffer from get- India will account for nearly a fifth of the global steel ting steel scraps with unreasonable prices (Wübbeke production by 2050 (International Energy Agency and Heroth 2014). In addition, such export restric- 2020), which means that ineffective governance on tion policy may increase the domestic steel scraps those unauthorized recycling firms will undermine supply in developed economies, which will lower the the global net zero efforts. local steel scraps prices and reduce the incentives of During the early stage of the study period, local recyclers to collect more steel scraps (Ohno et al more trade activities occurred within the same con- 2015). tinent due to their geographical proximity, which can reduce the corresponding transportation costs. 4.2. The dilemma of embodied AEs in the global Another reason is regional trade restriction policies. steel scraps recycling For example, the Basel Convention restricted EU The amount of AEs embodied in the global steel countries to export their non-hazardous and recyc- scraps trade has increased rapidly, with the total lable steel scraps to non-member countries (Wang volume in 2021 exceeding 1.5 times that of 2000. It et al 2020a). However, since these countries locate in indicates that more countries involved in the global the same continent and normally have similar eco- steel scraps trade. The recovery rate for some special nomic development levels and environmental gov- steel scraps, such as stainless-steel scraps, is normally ernance, it is difficult to have more internal steel high. A previous study shows that the recovery rates scraps trade. Then these countries began to seek new of Cr and Ni from stainless-steel scraps are nearly trade partners in other continents, especially those 95% (Team Stainless 2023). However, basic recovery developing countries with higher demands for steel technologies, such as shredding, crushing, magnetic 8 Environ. Res. Lett. 18 (2023) 094048 W Cai et al sorting, are typically applied by considering economy 4.3. Policy implications of scale (Reck and Graedel 2012). The recovery rates Based on the main findings of this study, we propose of embodied AEs are on average still low (Björkman two policy recommendations, including the optimiz- and Samuelsson 2014). In practice, downcycling is ation of steel scraps trade structure and technological still widely applied. It is difficult to achieve full recyc- cooperation. ling of AEs due to the lack of recycling considera- Our findings suggest that it makes sense for all tions during the design of complex products and dif- the involved countries to develop their steel scraps ficult screening of various steel scraps (Ohno et al trade policies to avoid potential risks. Those highly 2014). Additionally, most steel scraps are classified industrialized economies, such as the USA, the EU and traded based on their physical shapes (such as tri- and Japan, have significant influences on the global angular, rectangle, round, or even irregular shapes) in steel scraps supply chain. Therefore, key steel scraps the global market, indicating that the true values of import countries, such as Turkey and Republic of such AEs cannot be fully reflected in the steel scraps Korea, should seek to diversify their import part- markets (Ohno et al 2015). ners. Another consideration for these import coun- Our results show that the global steel scraps trade tries is how to avoid steel scraps price volatility has led a large amount of AEs to transfer from global or supply disruptions. Stockpiling is one solution, north countries to global south countries, especially but its effective implementation relies on careful for Co, V, Ni and Nb. These elements are now classi- national plan and international cooperation. Key sec- fied as critical minerals by many developed econom- ondary steel production countries (such as Turkey ies (MNRC 2016, European Comission 2017, USGS and India) should have more trade cooperation with 2017, DISER 2022). These countries have begun high-media countries (such as the United Kingdom, to restrict their export activities of such elements. Germany, Sweden, and the USA) so that they can bet- Unfortunately, the cross-border flows of AEs embod- ter express their trade opinions in the global steel ied in steel scraps have not received adequate atten- scraps market. In addition, some countries impor- tion. The absence of standards for recovering AEs ted cleaner steel scraps to produce high value-added is one reason for this phenomenon. For example, steel products, but exported low grade steel scraps Japan has implemented a comprehensive classifica- (Wang et al 2020a). For example, the copper contam- tion standard for steel scraps in order to differenti- ination in the exported steel scraps from the USA is ate steel scraps based on their AEs contents (Ohno 14% higher than that in its domestic recycling source et al 2014). However, this standard only covers the (Cooper et al 2020). To date, more countries start to contents of three AEs (Cr, Ni, and, Mo) and two restrict the import of low-grade steel scraps, which tramp elements (elements that may deteriorate steel means that steel scraps export countries should fur- properties during steel recycling, such as Cu and ther improve the quality of their steel scraps through Sn), but does not classify high-valued AEs such as pre-treatments. V, Nb, and Co. Also, we find that trade relations Additionally, we recommend that all countries between global north and south countries are gen- involved pay closer attention to those AEs embod- erally closer in embodied AEs trade networks. For ied in steel scraps. Although the development of instance, countries such as India, Spain, the United advanced recycling technologies for embodied AEs Kingdom, and South Africa belong to the same com- that are economically feasible still faces a number of munity in embodied Cr, Ni, Mo, Nb, Co, Pb, Al, Cu, technical difficulties, it is promising to seek poten- and Zn networks. These countries carry out intensive tial solutions through joint research and develop- international trade in alloyed steel scraps. However, ment efforts on laser, near-infrared, or x-ray sort- for global south countries, even if they obtain alloyed ing technologies by all trade countries (Reck and steel scraps through international trade, they may not Graedel 2012). The establishment of a formalized have the ability to extract and recycle AEs embod- international research body, including key stakehold- ied in these steel scraps. Thus, it is urgent to promote ers such as scientists, engineers, entrepreneurs and technological cooperation between global north and policymakers, is encouraged so that they can work global south countries. together to seek more innovative technologies on AE In addition, copper and tin are tramp elements in recovery. In order to make it effective, it is necessary steel scraps (Nakamura et al 2012). The recycling of to host regular meetings to help different stakehold- steel scraps may increase the concentration of such ers identify key technological problems, discuss how tramp elements in the recycled steel and eventually to collect adequate research funds, allocate research lead to thermal embrittlement, cracks and fractures of missions, and prepare a road map. For instance, secondary steel products (Daehn et al 2017, Yeşiltepe laser-induced breakdown spectroscopy is an emer- and Şeşen 2020). For instance, Turkey was the world’s ging technology for sorting steel scraps (Björkman largest importer of embodied Cu and embodied Sn. and Samuelsson 2014). Similarly, x-ray fluorescence Their recycling firms have to pay extra attention on sorter can help further improve the sorting efficiency their purchased steel scraps to avoid or at least reduce of steel scraps (Brooks et al 2019). Both technolo- the accumulation of Cu and Sn. gies should be further promoted so that they can 9 Environ. Res. Lett. 18 (2023) 094048 W Cai et al be better applied. Also, policymakers from different promote the overall resource efficiency. Finally, global countries may work together to release an interna- north countries should pay more attention on the tional standard on steel scraps trade so that the accu- corresponding environmental impacts and technical mulation of copper and tin in steel scraps can be mit- challenges associated with steel scraps trade, espe- igated. As such, industrial standards on the recovery cially in those global south countries. They should of AEs can help avoid high valued metals from down- help those involved global south countries through grade recycling. In addition, policymakers in relevant technology transfer, technical secondment, capacity countries should prepare economic incentives to pro- building activities and financial support. tect critical AEs, such as resource tax, financial sub- sidies and appropriate pricing. Finally, global north Data availability statement countries should actively help those involved global south countries through technology transfer, tech- All data that support the findings of this study are nical secondment, capacity building activities and fin- included within the article (and any supplementary ancial support since most global south countries do files). not have adequate financial, technological and insti- tutional abilities to effectively recover AEs embodied Acknowledgment in steel scraps. This study is financially supported by the National 5. Conclusions Key Research and Development Program of China (2019YFC1908501) and the Natural Science Steel scraps is a promising source to replace virgin Foundation of China (72088101, 71810107001). steel and can greatly contribute to the global net zero efforts. The embodied AEs have been transferred among different countries through the global steel References scraps trade, leading to the leakages and losses of such critical metals. This study maps the global flows of An H, Zhong W, Chen Y, Li H and Gao X 2014 Features and AEs embodied in steel scraps for the first time, and evolution of international crude oil trade relationships: a uncovers the key evolution features of international trading-based network analysis Energy 74 254–9 Awasthi A K and Li J 2017 Management of electrical and steel scraps trade network and its embodied AEs from electronic waste: a comparative evaluation of China and 2000 to 2021. We found that both the total trade India Renew. Sustain. Energy Rev. 76 434–47 amount and trade relations significantly increased, Björkman B and Samuelsson C 2014 Recycling of steel Handbook with a few countries (such as the USA, Germany, of Recycling (Elsevier) pp 65–83 Brooks L, Gaustad G, Gesing A, Mortvedt T and Freire F 2019 and Turkey) dominating the global steel scraps net- Ferrous and non-ferrous recycling: challenges and potential work. Also, we found that a few countries (such as the technology solutions Waste Manage. 85 519–28 United Kingdom, Germany, Sweden, and the USA) Brunner P H and Rechberger H 2016 Handbook of Material Flow were important hub countries and played a key role Analysis: For Environmental, Resource, and Waste Engineers (CRC Press) to connect this steel scraps trade network. In addi- Chen B, Li J S, Wu X F, Han M Y, Zeng L, Li Z and Chen G Q 2018 tion, the flows of AEs do not follow the patterns Global energy flows embodied in international trade: a of international steel scraps trade since the amounts combination of environmentally extended input–output of AEs embodied in steel scraps are actually much analysis and complex network analysis Appl. Energy 210 98–107 lower in several countries with significant steel scraps Cooper D R, Ryan N A, Syndergaard K and Zhu Y 2020 The trade volume. Also, a large amount of AEs was trans- potential for material circularity and independence in the ferred from countries in the global north (such as the U.S. steel sector J. Ind. Ecol. 24 748–62 USA, Germany and the United Kingdom) to coun- Cullen J M, Allwood J M and Bambach M D 2012 Mapping the global flow of steel: from steelmaking to end-use goods tries in the global south (such as China, India, and Environ. Sci. Technol. 46 13048–55 Turkey), especially the following elements, including Daehn K E, Cabrera Serrenho A and Allwood J M 2017 How will chromium (Cr), nickel (Ni), manganese (Mn) and copper contamination constrain future global steel molybdenum (Mo). From a global perspective, trad- recycling? Environ. Sci. Technol. 51 6599–606 Daigo I, Matsuno Y and Adachi Y 2010 Substance flow analysis of ing and recycling steel scraps may contribute to decar- chromium and nickel in the material flow of stainless steel in bonization efforts in the global steel industry and Japan Resour. Conserv. Recycl. 54 851–63 address raw material shortages in several countries. Dakua S 2019 Effect of determinants on financial leverage in This is of great significance for supporting the col- Indian steel industry: a study on capital structure Int. J. Finance Econ. 24 427–36 laborative implementation of SDG 12 (Responsible De Sa P and Korinek J 2021 Resource efficiency, the circular Consumption and Production) and SDG 13 (Climate economy, sustainable materials management and trade in Action). However, current steel scraps prices may not metals and minerals OECD Trade Policy Papers No. 245 fully reflect the true values of such embodied critical Diener D L and Tillman A-M 2015 Component end-of-life management: exploring opportunities and related benefits metals, leading to the losses of these valuable metals. of remanufacturing and functional recycling Resour. Consequently, it is necessary to prepare appropri- Conserv. Recycl. 102 80–93 ate trade policies and circular economy strategies to DISER 2022 2022 Critical Minerals Strategy 10 Environ. Res. Lett. 18 (2023) 094048 W Cai et al Du R, Wang Y, Dong G, Tian L, Liu Y, Wang M and Fang G 2017 emissions in China’s iron and steel sector One Earth A complex network perspective on interrelations and 5 932–43 evolution features of international oil trade, 2002–2013 Liu G, Bangs C E and Müller D B 2013 Stock dynamics and Appl. Energy 196 142–51 emission pathways of the global aluminium cycle Nat. Clim. European Comission 2017 Study on the Review of the List of Change 3 338–42 Critical Raw Materials Liu G and Müller D B 2013 Mapping the global journey of European Commission 2021 Proposal for a Regulation of the anthropogenic aluminum: a trade-linked multilevel material European Parliament and of the Council on Shipments of flow analysis Environ. Sci. Technol. 47 11873–81 Waste and Amending Regulations (EU) No 1257/2013 and Liu X, Stanley H E and Gao J 2016 Breakdown of interdependent (EU) No 2020/1056 directed networks Proc. Natl Acad. Sci. 113 1138–43 Fan Z and Friedmann S J 2021 Low-carbon production of iron Liu Y, Ma R, Guan C, Chen B and Zhang B 2022 Global trade and steel: technology options, economic assessment, and network and CH4 emission outsourcing Sci. Total Environ. policy Joule 5 829–62 803 150008 Gao Z, Geng Y, Xiao S and Zhuang M 2022a Mapping the global Ma Z, Yang Y, Chen W-Q, Wang P, Wang C, Zhang C and Gan J anthropogenic chromium cycle: implications for resource 2021 Material flow patterns of the global waste paper trade efficiency and potential supply risk Environ. Sci. Technol. and potential impacts of China’s import ban Environ. Sci. 56 10904–15 Technol. 55 8492–501 Gao Z, Geng Y, Zeng X, Tian X, Yao T, Song X and Su C 2022b MNRC 2016 Mineral Resources Planning (2016–2020) Evolution of the anthropogenic chromium cycle in China J. Nakajima K, Ohno H, Kondo Y, Matsubae K, Takeda O, Miki T, Ind. Ecol. 26 592–608 Nakamura S and Nagasaka T 2013 Simultaneous material Ge J, Wang X, Guan Q, Li W, Zhu H and Yao M 2016 World rare flow analysis of nickel, chromium, and molybdenum used in earths trade network: patterns, relations and role alloy steel by means of input–output analysis Environ. Sci. characteristics Resour. Policy 50 119–30 Technol. 47 4653–60 Gerber Group 2022 Stainless espresso: ferrous scrap the new hard Nakamura S, Kondo Y, Matsubae K, Nakajima K, Tasaki T and currency, UAE imposes export ban (available at: https:// Nagasaka T 2012 Quality- and dilution losses in the steelnews.biz/ferrous-scrap-new-hard-currency-uae-export- recycling of ferrous materials from end-of-life passenger ban/) cars: input-output analysis under explicit consideration of Glöser S, Soulier M and Tercero Espinoza L A 2013 Dynamic scrap quality Environ. Sci. Technol. 46 9266–73 analysis of global copper flows. Global stocks, postconsumer Nakamura S, Kondo Y, Nakajima K, Ohno H and Pauliuk S 2017 material flows, recycling indicators, and uncertainty Quantifying recycling and losses of Cr and Ni in steel evaluation Environ. Sci. Technol. 47 6564–72 throughout multiple life cycles using matrace-alloy Environ. Graedel T E, Allwood J, Birat J-P, Buchert M, Hagelüken C, Sci. Technol. 51 9469–76 Reck B K, Sibley S F and Sonnemann G 2011 What do we Neşer G, Ünsalan D, Tekoğul N and Stuer-Lauridsen F 2008 The know about metal recycling rates? J. Ind. Ecol. 15 355–66 shipbreaking industry in Turkey: environmental, safety and Graedel T E, Van Beers D, Bertram M, Fuse K, Gordon R B, health issues J. Clean. Prod. 16 350–8 Gritsinin A, Kapur A, Klee R, Lifset R and Memon L 2004 Ohno H, Matsubae K, Nakajima K, Kondo Y, Nakamura S, Multilevel cycle of anthropogenic copper Environ. Sci. Fukushima Y and Nagasaka T 2017 Optimal recycling of Technol. 38 1242–52 steel scrap and alloying elements: input-output based linear Harvey L D D 2021 Iron and steel recycling: review, conceptual programming method with its application to end-of-life model, irreducible mining requirements, and energy vehicles in Japan Environ. Sci. Technol. 51 13086–94 implications Renew. Sustain. Energy Rev. 138 110553 Ohno H, Matsubae K, Nakajima K, Kondo Y, Nakamura S and Hertwich E G, Ali S, Ciacci L, Fishman T, Heeren N, Masanet E, Nagasaka T 2015 Toward the efficient recycling of alloying Asghari F N, Olivetti E, Pauliuk S and Tu Q 2019 Material elements from end of life vehicle steel scrap Resour. Conserv. efficiency strategies to reducing greenhouse gas emissions Recycl. 100 11–20 associated with buildings, vehicles, and electronics—a Ohno H, Matsubae K, Nakajima K, Nakamura S and Nagasaka T review Environ. Res. Lett. 14 043004 2014 Unintentional flow of alloying elements in steel during International Energy Agency 2021 The Role of Critical Minerals in recycling of end-of-life vehicles J. Ind. Ecol. 18 242–53 Clean Energy Transitions Ohno H, Matsubae K, Nakajima K, Nansai K, Fukushima Y and International Energy Agency 2020 Iron and Steel Technology Nagasaka T 2016 Consumption-based accounting of steel Roadmap alloying elements and greenhouse gas emissions associated International Information Group 2022 Russian govt introducing with the metal use: the case of Japan J. Econ. Struct. 5 28 quota on exporting scrap metal as of June 1, duty to be 290 Özdemir A, Günkaya Z, Özkan A, Ersen O, Bilgiç M and Banar M euros/tonne when exceeded (available at: https://interfax. 2018 Lifecycle assessment of steel rebar production with com/newsroom/top-stories/79661/) induction melting furnace: case study in Turkey J. Hazard. Jackson M O 2010 Social and Economic Networks (Princeton Toxic Radioact. Waste 22 04017027 University Press) Pacini H, Shi G, Sanches-Pereira A and Filho A C D S 2021 Jiang M, An H, Gao X, Liu S and Xi X 2019 Factors driving global Network analysis of international trade in plastic scrap carbon emissions: a complex network perspective Resour. Sustain. Prod. Consum. 27 203–16 Conserv. Recycl. 146 431–40 Panasiuk D, Daigo I, Hoshino T, Hayashi H, Yamasue E, Laner D, Rechberger H and Astrup T 2014 Systematic evaluation Tran D H, Sprecher B, Shi F and Shatokha V 2022 of uncertainty in material flow analysis J. Ind. Ecol. International comparison of impurities mixing and 18 859–70 accumulation in steel scrap J. Ind. Ecol. 26 1040–50 Lee H and Sohn I 2015 Global scrap trading outlook analysis for Pauliuk S, Milford R L, Müller D B and Allwood J M 2013a The steel sustainability J. Sustain. Metall. 1 39–52 steel scrap age Environ. Sci. Technol. 47 3448–54 Lee R 2023 Argentina prohibits exports of aluminum and metal Pauliuk S, Wang T and Müller D B 2013b Steel all over the world: scrap until 2024 (available at: www.yieh.com/en/NewsItem/ estimating in-use stocks of iron for 200 countries Resour. 139480) Conserv. Recycl. 71 22–30 Li Q, Gao T, Wang G, Cheng J, Dai T and Wang H 2019 Dynamic Price A and Nance S 2009 Export barriers and global trade in raw analysis of iron flows and in-use stocks in China: 1949–2015 materials: the steel industry experience Report to the Raw Resour. Policy 62 625–34 Materials Committee of the OECD (Wiley) Li Z and Hanaoka T 2022 Plant-level mitigation strategies could Rathore G J S 2020 Circulating waste, circulating bodies? A critical enable carbon neutrality by 2060 and reduce non-CO2 review of E-waste trade Geoforum 110 180–2 11 Environ. Res. Lett. 18 (2023) 094048 W Cai et al Reck B K and Graedel T E 2012 Challenges in metal recycling van Vuuren D P et al 2018 Alternative pathways to the 1.5 ◦ C Science 337 690–5 target reduce the need for negative emission technologies Recycling Today 2017 China retains ferrous scrap export tax Nat. Clim. Change 8 391–7 (available at: www.recyclingtoday.com/news/china-ferrous- Wang C, Huang X, Lim M K, Tseng M-L and Ghadimi P 2020a scrap-export-tax-steel/) Mapping the structural evolution in the global scrap copper Ren L, Zhou S, Peng T and Ou X 2021 A review of CO2 emissions trade network J. Clean. Prod. 275 122934 reduction technologies and low-carbon development in the Wang C, Zhao L, Lim M K, Chen W-Q and Sutherland J W 2020b iron and steel industry focusing on China Renew. Sustain. Structure of the global plastic waste trade network and the Energy Rev. 143 110846 impact of China’s import Ban Resour. Conserv. Recycl. Schoot Uiterkamp B J, Azadi H and Ho P 2011 Sustainable 153 104591 recycling model: a comparative analysis between India and Wang P, Ryberg M, Yang Y, Feng K, Kara S, Hauschild M and Tanzania Resour. Conserv. Recycl. 55 344–55 Chen W-Q 2021a Efficiency stagnation in global steel Schütz H, Moll S and Bringezu S 2004 Globalisation and the production urges joint supply- and demand-side mitigation shifting environmental burden: material trade flows of the efforts Nat. Commun. 12 2066 European Union; which globalisation is sustainable? Wang T, Müller D B and Graedel T E 2007 Forging the Wuppertal Institut für Klima, Umwelt, Energie anthropogenic iron cycle Environ. Sci. Technol. 41 5120–9 Shao L, Hu J and Zhang H 2021 Evolution of global lithium Wang W, Chen W-Q, Diao Z-W, Ciacci L, Pourzahedi L, competition network pattern and its influence factors Eckelman M J, Yang Y and Shi L 2021b Multidimensional Resour. Policy 74 102353 analyses reveal unequal resource, economic, and Su C, Geng Y, Zeng X, Gao Z and Song X 2023 Uncovering the environmental gains and losses among the global aluminum features of nickel flows in China Resour. Conserv. Recycl. trade leaders Environ. Sci. Technol. 55 7102–12 188 106702 Wang W, Li Z and Cheng X 2019 Evolution of the global coal Sun X, Hao H, Liu Z, Zhao F and Song J 2019 Tracing global trade network: a complex network analysis Resour. Policy cobalt flow: 1995–2015 Resour. Conserv. Recycl. 149 45–55 62 496–506 Sun X, Hao H, Zhao F and Liu Z 2017 Tracing global lithium flow: Wang X, Wang A, Zhong W, Zhu D and Wang C 2022 Analysis of a trade-linked material flow analysis Resour. Conserv. Recycl. international nickel flow based on the industrial chain 124 50–61 Resour. Policy 77 102729 Tan J, Wehde M V, Brønd F and Kalvig P 2021 Traded metal scrap, Wasserman S and Faust K 1994 Social network analysis: methods traded alloying elements: a case study of Denmark and and applications implications for circular economy Resour. Conserv. Recycl. Wübbeke J and Heroth T 2014 Challenges and political solutions 168 105242 for steel recycling in China Resour. Conserv. Recycl. Team Stainless 2023 Global life cycle of stainless steel (available at: 87 1–7 www.worldstainless.org/news/global-life-cycle-of-stainless- Yamaguchi S 2018 International trade and the transition to a more steel/) resource efficient and circular economy: a concept paper The Scrap Metal Council 2015 The Scrap Metal Act Yeşiltepe S and Şeşen M K 2020 High-temperature oxidation The World Steel Association 2020 Steel Statistical Yearbook 2019 kinetics of Cu bearing carbon steel SN Appl. Sci. 2 1–8 Tokito S, Kagawa S and Nansai K 2016 Understanding Zheng S, Zhou X, Zhao P, Xing W, Han Y, Hao H and Luo W 2022 international trade network complexity of platinum: the Impact of countries’ role on trade prices from a nickel chain case of Japan Resour. Policy 49 415–21 perspective: based on complex network and panel regression UN Comtrade 2023 International trade statistics database analysis Resour. Policy 78 102930 (available at: https://comtradeplus.un.org/) Zhong W, Dai T, Wang G, Li Q, Li D, Liang L, Sun X, Hao X and USGS 2017 Critical Mineral Resources of the United States: Jiang M 2018 Structure of international iron flow: based on Economic and Environmental Geology and Prospects for substance flow analysis and complex network Resour. Future Supply (Geological Survey) Conserv. Recycl. 136 345–54 van Soest H L, den Elzen M G J and van Vuuren D P 2021 Zhou X, Zhang H, Zheng S and Xing W 2022 The global recycling Net-zero emission targets for major emitting countries trade for twelve critical metals: based on trade pattern and consistent with the Paris Agreement Nat. Commun. 12 2140 trade quality analysis Sustain. Prod. Consum. 33 831–45 12