In-use Stock Research Articles

Impact of circular economy on the long-term allocation structure of primary and secondary lithium

Lithium is key for a clean energy transition but faces sustainability challenges in the global supply. Here, we use a bottom-up approach to study the evolution of the global lithium-ion battery industry from 2023 to 2050. The supply and demand trends are predicted to determine the supply potential and allocation structure of primary and secondary lithium. The results indicate a projected global lithium demand of 1.93 million metric tons in 2050, a significant increase of 26.2 times compared to 2023. In the process of global lithium resources shifting from underground reserves to in-use stocks, population and Gross Domestic Product (GDP) influence regions’ lithium endowment and per capita primary consumption, respectively. If the European Union’s new battery regulation is implemented globally, then it is projected to reduce global primary lithium consumption by 1.03 million metric tons by 2050, with a 53.48% decrease in the proportion of primary lithium consumption.

Mapping chromium flows in China's stainless-steel product chain: A product-level substance flow analysis

Chromium (Cr) is a critical metal that supports the development of China's emerging industries. Approximately 82% of China's Cr is used to manufacture stainless steel. However, the stainless-steel product chain has often been referred to as a “black box” in Cr substance flow analysis, leading to limited guidance for Cr management. This study aims to fill this gap by analysing Cr flows and in-use stock patterns in China's stainless-steel product chain from 2012 to 2022. During this period, China's Cr consumption experienced significant growth, increasing by over 10% annually, with 90.4% being imported. The Energy Infrastructure sector emerged as the dominant consumer of Cr (8,099 kt) and in-use stock (7,702 kt), Heavy Machinery products accounting for the highest Cr consumption (3,269 kt). Conducting product-level SFA is crucial for sustainable Cr resource management and environmental policy-making.

Urbanization inequality: evidence from vehicle ownership in Chinese cities

Unequal outcomes resulting from urbanization can pose a significant challenge to sustainable development. Vehicles are an important urbanization dimension as a critical component of urban infrastructure by providing mobility and accessibility to social services. China’s vehicle ownership (referred to as in-use vehicle stocks) has been growing quickly since 2000, but its per capita stocks are still much lower than that in developed economies. This raises the question of whether and when China’s vehicle stocks will reach a peak level close to that in the developed countries. By analyzing vehicle stocks in 283 Chinese cities during 2001–2018, we have the following findings: (1) vehicle stocks are predominantly distributed in northern and eastern coastal cities and provincial capital cities; (2) inequality in vehicle ownership rates between cities shows a declining trend at both national and region scales; (3) the growth of vehicle ownership rates follows an S-shape curve and most cities are still at the early stage of motorization; (4) China is likely to have a lower saturation level of vehicle ownership rate. These results could help to accurately forecast future vehicle demand in China, estimate the resulting environmental impacts, and explore strategies to achieve carbon neutrality in transportation.

Evolving cobalt cycle and urban mines in the EU, 1988–2020

Urban mines are vital for resource security and resilience, but the intricacies of their recycling processes are often overlooked. This study uses dynamic Material Flow Analysis to delve into the EU's cobalt cycle from 1988 to 2020, focusing on urban cobalt mining potential. We observed a significant shift in EU cobalt consumption patterns, with the demand for electric vehicle batteries surpassing that for superalloys, thereby positioning batteries as the primary cobalt consumers. Moreover, batteries increasingly dominate the cobalt in-use stock. The recycling process experiences substantial losses, especially in collection and pretreatment stages, reaching up to 87 %. Our findings indicates that urban cobalt mines could account for 57–66 % of the EU's total cobalt consumption, amounting to 166–193 kt in a high scenario. These insights emphasize the changing dynamics of the EU cobalt cycle and the importance of efficient urban cobalt mine management.

Mapping Plastic and Plastic Additive Cycles in Coastal Countries: A Norwegian Case Study.

The growing environmental consequences caused by plastic pollution highlight the need for a better understanding of plastic polymer cycles and their associated additives. We present a novel, comprehensive top-down method using inflow-driven dynamic probabilistic material flow analysis (DPMFA) to map the plastic cycle in coastal countries. For the first time, we covered the progressive leaching of microplastics to the environment during the use phase of products and modeled the presence of 232 plastic additives. We applied this methodology to Norway and proposed initial release pathways to different environmental compartments. 758 kt of plastics distributed among 13 different polymers was introduced to the Norwegian economy in 2020, 4.4 Mt was present in in-use stocks, and 632 kt was wasted, of which 15.2 kt (2.4%) was released to the environment with a similar share of macro- and microplastics and 4.8 kt ended up in the ocean. Our study shows tire wear rubber as a highly pollutive microplastic source, while most macroplastics originated from consumer packaging with LDPE, PP, and PET as dominant polymers. Additionally, 75 kt of plastic additives was potentially released to the environment alongside these polymers. We emphasize that upstream measures, such as consumption reduction and changes in product design, would result in the most positive impact for limiting plastic pollution.

Anthropogenic cycles of praseodymium in China: 2000–2020

Praseodymium (Pr) is one of critical rare earth elements (REEs), which is widely used in clean energy technologies and home appliances. With the increasing demand of renewable energy, it is necessary to uncover the features of Pr stocks and flows through its whole life cycle. China is the largest REEs supplier in the world, but its Pr stocks and flows remain unclear. Therefore, this study investigates the anthropogenic Pr cycle in China for the period of 2000–2020 by applying dynamic material flow analysis. The results show that a total of 176 Gg Pr flowed into the Chinese anthropogenic system over the past two decades. Pr supply reached 10.8 Gg in 2020, while Pr demand reached 9.2 Gg in 2020, respectively. The top three Pr consumption fields were wind turbines (2.5 Gg), refrigerators (431 Mg), and electric vehicles (403 Mg) in 2020, with annual growth rates of 40%, 32%, and 86% during the study period, respectively. The largest in-use Pr stock came from wind turbines (with a figure of 18.8 Gg) in 2020, followed by air conditioners (5.5 Gg) and wash machines (3.2 Gg). The largest end-of-life flow came from air conditioners in 2020, with a figure of 847 Mg. Based on these results, three policy recommendations are proposed, including stable Pr supply, appropriate Pr recycling and recovery, and synergetic management with neodymium.

Quantifying provincial in-use stocks of rare earth to identify urban mining potentials in the Chinese mainland

Recycling of rare earth elements (REE) can help to offset the increasing demand for REE minerals and enhance the diversification of the REE supply chain. The development of low-carbon technologies, such as new energy vehicles and wind turbines has expedited the accumulation of REE as “urban mines”. This trend offers prospects for the progress of REE recycling initiatives targeting end-of-life products. This study conducts a dynamic material flow analysis (combined top-down and bottom-up method) of nine products containing NdFeB permanent magnets (their scrap is regarded as the most important secondary resource of rare earth) in the Chinese mainland at a provincial level to identify end-of-life products and provinces with high urban mining potentials. Results indicate that e-bikes, wind turbines, and air conditioners have the most significant REE recycling potentials in the Chinese mainland. Provinces with large populations and robust economies, such as Guangdong and Jiangsu, exhibit greater potential for REE recycling. This study illustrates significant provincial disparities in the end-of-life recycling potentials of REEs in the Chinese mainland and highlights the significance of provincial-level assessments of urban mining potential in the planning of the REE recycling industry.

Ensuring the sustainable supply of semiconductor material: A case of germanium in China

The semiconductor industry relies on the sustainable supply of critical mineral resources, such as Germanium (Ge), a key metal used in making electronics, fiber cables and solar cells. However, since Ge is a companion element, its primary production is constrained by the availability of host minerals such as zinc and coal. As such, its recycling is challenging since both recycling networks and technologies are still in its early infancy. There are increasing concerns on how to meet with the future demand for Ge due to its limited supply. This study aims to uncover the metabolic characteristics of the Ge cycle in China for the period of 2002–2021 from a whole life cycle perspective by employing a dynamic material flow analysis. The results show that China's demand for Ge had increased from 19.16 tons in 2002 to 85.87 tons in 2021. Fiber cables and infrared optical instruments consumed the most Ge resource, accounting for 54.59% and 36.76% of the total Ge consumption, respectively. The in-use Ge stock had increased more than 40 folds, implying a substantial potential for future recycling. The majority of Ge was extracted from coal ash and zinc concentrates, with figures of 1086.92 tons and 585.27 tons respectively, while only 13.45 tons of Ge were recovered from those end-of-life products. Furthermore, the Ge loss reached 1586.31 tons at the production stage. The Ge stock in those intermediate products has gradually decreased. The cumulative Ge export amount contained in various products was 655.64 tons, mainly dominated by intermediate products, while the share of final products increased in recent years. Based on these findings, several policy recommendations are proposed, including improving Ge production efficiency and expanding Ge supply sources, establishing a comprehensive Ge recycling system, and upgrading the entire Ge industrial chain. These policies can help better cope with the challenges that the global semiconductor supply chain is facing.

Mapping the evolution of manganese flows and stocks in China from 2000 to 2021

Manganese is a strategic metal that has been widely applied in the steelmaking industry and the emerging energy batteries industry. China is the largest manganese importer and consumer, but the critical features of its manganese metabolisms, including its supply and demand, trade, and waste management, remain unclear. By applying dynamic material flow analysis (DMFA) method, this research investigates the evolution of China’s anthropogenic manganese flows and stocks during the period of 2000 to 2021. We found that the demand for manganese had increased almost tenfold in China from 2000 to 2021, mainly used for steelmaking, while the surging demand for manganese in energy batteries had gradually increased. However, China highly relied on importing manganese concentrates due to its limited manganese resources. The cumulative in-use manganese stocks also increased by tenfold and reached approximately 168 million tons (Mt). In addition, manganese flow from the end-of-life (EoL) final products reached 12 Mt in 2021, but few of them were recycled, implying a huge recycling potential. These findings provide valuable insights to prepare more appropriate manganese resource management policies, such as improving domestic mining technologies, enhancing manganese recycling, and diversifying the supply of manganese resources, so that the overall manganese resource efficiency can be improved.

Multi-typology and multi-scale maps of the in-use building material stock in China

China's rapid urban expansion and population migration have led to a substantial increase in building material stocks (MS). Understanding these stocks is crucial for effective planning and managing the built environment. This study analyzed in-use building MS in China from 2000 to 2020 at different spatial scales and resolutions and employed typological data as a bridge addressing information gaps in non-residential buildings and the spatial scale discontinuity issue in MS analysis. At the macro scale, MS in China increased from 70 gigatons (Gt) in 2000 to 133 Gt in 2020. Non-residential and non-urban MS played substantial roles, constituting 41.8 % and 47.9 % in 2020, respectively. In highly urbanized regions, the proportion of residential building MS decreased due to the prevalence of more functional buildings. Some southern provinces had MS from rural areas even exceeding 50 %, emphasizing the importance of considering rural areas in construction resource management. At a high-resolution scale using GIS data, differences emerged between the analysis and statistical data. These differences, especially in estimating residential and commercial building MS, may be attributed to the mixed-use of building types in Chinese cities or unclear delineations of land use types. We advocate for further research to explore these variations, establishing consistent MS methods across different spatial scales and providing decision-makers with effective data support and analytical tools.

Uncovering the key features of platinum metabolism in China during 2001–2022: A dynamic material flow analysis

Platinum is a critical mineral resource and has been called the “vitamin” of the technology industry as it is widely utilized in diverse fields such as automobiles, petroleum, chemicals, medicine, jewelry, and electronics. The demand for platinum is increasing, but its reserve is limited, especially in China, a major platinum user in the world. This study aims to track the platinum cycle in China for the period of 2001–2022 by employing dynamic material flow analysis so that the key features of platinum metabolism in China can be identified. Our results show that the total production of domestic platinum mining accounted for only 1.27% of the national platinum supply. China had to import platinum resource to meet with its increasing demand. The jewelry sector contributed the largest platinum consumption due to the preference of the Chinese consumers. There are two recycling routes for all the retired platinum-containing products, including both closed-loop and open-loop routes. Also, the total illegal imported platinum scraps reached 131.27 tons, accounting for 47.57% of the total open-loop recycled platinum. China's platinum in-use stocks increased from 44.23 tons in 2001 to 824.49 tons in 2022. As a result, the end-of-life platinum scraps increased from 0 tons in 2001 to 65.83 tons in 2022. In addition, China primarily imported platinum semi-finished products to meet its domestic demand, but mainly exported platinum scraps and finished products to other countries. Based on these research findings, policy recommendations are proposed by considering the Chinese realities, covering political, technological, and industrial cooperation dimensions. The results of this study provide valuable insights to those decision makers so that they can prepare more effective platinum resource policies.

Boosted efficiency and unsaturated material stock growth in China's megacities: Accelerating as urbanization approaches 80 %

Buildings, infrastructure, and durable goods are essential for human activities. Understanding their relationship with socioeconomic development is crucial for optimizing resource allocation in urban settings, thereby enhancing efficiency and lessening environmental impact. This study delves into the urban material stock evolution in China's megacities, spanning 111 distinct end-use stocks. From 1978 to 2018, in-use stocks witnessed a substantial surge, increasing from a modest <350 Mt to an astounding 819–3130 Mt across cities—an average annual growth rate ranging from of 4.7 to 15.2 %. This growth was paralleled by improvements in stock productivity, associated with reductions in CO2 emissions by 154–505 Mt and conservation of significant amounts of energy and food resources. As urbanization approaches the 80 % mark, a mere 1 % rise results in considerable increments of 13.5, 1.9, and 0.6 t in per capita stocks of buildings, infrastructure, and durable goods. Our results shed light on strategies for resource circulation, stock management, and sustainable urban future trajectories.

Sustain China's copper resources with domestic mining, trading, and recycling

Rapid urbanization and industrialization made China the world's largest refined copper producer and consumer. Insufficient copper ore reserves necessitated significant imports and scrap copper recycling. Using material flow and scenario analysis, this study examined historical copper supply and assessed future supply-demand balance. The results show that China's refined copper consumption soared from 2.3 Kt in 1949 to 14.43 Mt in 2020, with imports rising from 1.5 Kt to 11.77 Mt, resulting in a 75 % external dependence. In addition, primary copper importers were concentrated in the Americas. In 2020, China accumulated around 120 Mt of in-use stocks, enabling urban mineral resource development. Forecasted results indicate a persistent copper supply deficit. Recycling copper scrap is crucial to bridge the supply-demand gap. This study enhances understanding of copper's historical supply and consumption, providing policymakers with suggestions for sustainable copper resource management.

Multinational dynamic steel cycle analysis reveals sequential decoupling between material use and economic growth

Decoupling material use from economic growth is a prerequisite for alleviating the adverse effects of anthropogenic material use and achieving the Sustainable Development Goals. In this study, we combine dynamic material flow analysis with decoupling analysis to examine the relationship between the iron and steel cycle and economic growth in 23 industrialized countries from 1860 to 2018. Specifically, we employ both the quadratic and asymptotic functions to fit the relationship of per capita steel flow/stock indicators at six life cycle stages, including domestic production and apparent consumption of iron ore, pig iron, crude steel, finished steel, and fabricated steel, as well as in-use stock, against per capita GDP. A sequential decoupling between steel flow/stock indicators and GDP growth along the iron and steel cycle is evident. The historical dynamics of the comparative advantage of material flow indicators depict the wave-like geographic diffusion of industrialization. The mechanisms underlying the evolution of material-economy relationship can be attributed to resource endowments, industry policies, trade effects, and lock-in effect of in-use stock. Understanding this phenomenon can facilitate policy-making to promote dematerialization and improve material efficiency in developing countries.

Material resource decoupling dilemma: Convergence and traps of in-use stock productivity in national economy development

Various studies have suggested decoupling material stock from economic output as an important measure for promoting sustainable development. Here, we develop three theoretical hypotheses to describe the evolution features and economic effects of material stock intensity, and predict in theory that (1) Countries with higher material stock intensity are more likely to decouple economic growth from material stock. (2) Material stock intensity follows convergence trends. (3) Higher material stock intensity leads to higher long-run economic growth rates. To examine the adaptability of these hypotheses, we choose steel in-use stock as the proxy for the material capital stock and use panel data in 85 countries from 1950 to 2018 to conduct empirical analysis. Our empirical results in most countries support the theoretical predictions of the hypotheses. In particular, a 0.1t/k$ increase in steel stock intensity leads to a 2.12% increase in the probability of decoupling between steel stock and economic output next year and a 0.34% increase in the long-run GDP per capita growth rate annually. Moreover, steel stock intensity converges to approximately 0.25t/k$ to 0.35t/k$ at mature development stages. We predict that, except China, which is expected to follow decoupling trends, other large developing economies will couple economic output with steel stock. However, the shape of intensity curves is still uncertain for highly developed countries in the future.

Mobilizing materials to enable a fast energy transition: A conceptual framework

Limiting climate heating while meeting basic needs for all necessitates large-scale deployment of renewable energy. Understanding the dynamics of mobilizing materials for the transition requires considering: 1) availability of resources in the environment and technosphere; 2) accessibility depending on resource quality and available technologies; 3) processability depending on energy availability, processing capacity, and impacts on planetary boundaries; and 4) operability depending on social acceptance and geopolitical agreements. Materials can be mobilized through four routes: 1) increasing primary production; 2) diverting existing primary production; 3) repurposing in-use stocks; and 4) re-mining wastes and emissions. The interplay of these enabling factors, material efficiency in design, and substitution with materials that are easier to mobilize determines the maximum possible rate of material mobilization and consequently the energy transition itself. This paper presents and discusses a framework to explore joint energy-material transformations, enabling to consider material aspects in transition modelling and guide technological developments.

Global copper cycles in the anthroposphere since the 1960s

This study characterizes the copper cycle, quantifying flows, stocks, and losses from 1960 to 2020, and explores global copper supply and demand under six scenarios until 2050. Results show substantial growth in copper production, consumption, and trade over six decades, with around 761 Tg of copper extracted, resulting in 483 Tg in-use stocks. Monte Carlo simulations indicate an 11.4 % uncertainty. These stocks, redistributed globally, form independent secondary resources for each country, with Chile, Peru and Australia holding dominant underground reserves, and China and the United States primarily having above-ground stocks. Targeted policies are needed to close the copper cycle due to current loss rates. Copper shortages are anticipated around 2040, further exacerbated by the development of low-carbon technologies and extended copper product lifespans, but mitigated by alternative technologies and increased recycling rates.

Material requirements and impacts of the building sector in the Shared Socioeconomic Pathways

The significant weight of the building sector in global material demand has been addressed in several publications, but a lack of consideration of the energy-materials nexus was identified. To fill this gap, we developed a stock-flow dynamic model from 1950 to 2100, using scenarios of the International Energy Agency and the Shared Socioeconomic Pathways of the academic literature. We find that (i) the increasing stocks in the less developed countries results in a rise of the inflows; (ii) strong inequalities are observed in the in-use stocks per capita of materials in the SSPs, despite optimistic material intensities projection, (iii) a growing materials demand translates into larger final energy demand of material production, which could question the feasibility of some low-energy demand scenarios, and that (iv) the recycled concrete aggregated display a significant potential to enhance the reduction of accumulated concrete stocks in landfills and green concrete could decrease the energy demand of concrete production. We furthermore highlight the crucial temporal aspect of policies to successfully implement these solutions, as long lifetimes are observed in the building sector.

Dynamic material flow analysis of rhenium in China for 2011–2020

Rhenium (Re) is one rare and heavy metal element that plays an important role in various fields, such as aerospace applications, petroleum industry, and power generation. However, less attention has been paid to its metabolism patterns. This study employs a dynamic material flow analysis method to investigate the anthropogenic Re cycle in China from 2011 to 2020. The results show that the annual demand for Re had increased from 7.02 tons to 10.41 tons during the study period, in which 44.91% of the total Re was used to produce petro-reforming catalysts and 32.87% of the total Re was used to make aero-engines. A total of 54.94 tons of Re became in-use stock and 18.55 tons were discarded. A significant Re loss (55.92 tons) was generated in the refining and separation stage, mainly due to cost and technological constraints. On the supply side, the domestic primary Re production remained stable in China, but unable to meet the market demand. Therefore, China has to rely on importing Re products, with a net import reliance (NIR) of more than 75% in recent years. The imported Re had increased from 8.68 tons in 2011 to 18.99 tons in 2020. About 85.4% of the imported final products were aero-engines. By identifying several problems hindering the sustainable use of Re in China, we proposed several policy recommendations to improve the overall Re resource efficiency, such as policy and economic supports for Re recycling, enhancing Re's production and utilization technologies, and strengthening Re supply resilience.

Mining the in-use stock of energy-transition materials for closed-loop e-mobility

The decarbonization of transportation is essential to achieve a carbon neutral planetary society. However, the turn to electromobility is based on advanced technologies (e.g., lithium-ions batteries) that tied our development to many functional materials with problematic supply. In this study, we apply prospective dynamic material flow analysis to explore the potentials for closing material cycles while meeting a full transition to electric for a set of energy-transition materials (ETMs) including lithium, cobalt, nickel, manganese, and natural graphite. Three demand scenarios are applied to develop trajectories for ETM demand, their in-use stock, and derive the potentials to which recycling can substitute for virgin material extraction at the global scale to 2065.Our results estimate that ETM inflow to use could increase between 20 and 50 times by 2065. However, secondary supply will hardly enable the achievement of circularity in material cycles in the next decades so that the supply of ETMs will remain mainly based on primary material extraction. Nevertheless, from 2040 onwards, recycling volumes could meet up to more than 80% of demand and represent a viable alternative to mining. If the ideal scenario is realized, government policies could have the potential for achieving the dual goal of decarbonizing e-mobility and securing sustainable access to ETMs already in the middle of 2050s. However, the combined commitment and efforts across the value chain of policymakers, companies involved in the cycle, and consumers will be needed to fully realize the great potential for circular economy to work for e-mobility.