Uncovering Availability of the Secondary Iron Resources in China: Integrating Material Flow Analysis and Secondary Resources Reserve Assessment.

As the largest iron and steel producer, China still cannot meet its demand of iron and steel only through domestic primary supply in the last few decades. Hence, secondary iron resources are increasingly significant in meeting China's iron supply and demand balance. However, the secondary iron resource availability in China and how it impacts the future supply demand balance were still insufficiently discussed. In this work, we developed a material flow analysis and secondary resources reserve assessment (MFA-SRRA) integrated model, assessed secondary iron resources availability, and conducted a supply demand analysis through nine scenarios for irons in China. The results showed that China's secondary iron reserves will increase from 8.9 Gt in 2021 to 14.04 to 19.01 Gt in 2050. With the increasing secondary iron supply, more than 60% of iron ore as a source of steelmaking can be replaced by 2050. Landfills, as a significant reserve of iron but always ignored, will accumulate 1.42-1.51 Gt secondary iron resources by 2050 and should be noticed to be mined and utilized in the future. Last, we suggest that promoting innovation in landfill mining technology and making sustainable material management policies are urgent to prevent these secondary iron resources from becoming real waste.

Tracking Three Decades of Global Neodymium Stocks and Flows with a Trade-Linked Multiregional Material Flow Analysis.

Neodymium (Nd), an essential type of rare earth element, has attracted increasing attention in recent years due to its significant role in emerging technologies and its globally imbalanced demand and supply. Understanding the global and regional Nd stocks and flows would thus be important for understanding and mitigating potential supply risks. In this work, we applied a trade-linked multiregional material flow analysis to map the global and regional neodymium cycles from 1990 to 2020. We reveal increasingly complex trade patterns of Nd-containing products and a clearly dominant but slightly weakening role of China in the global Nd trade (for both raw materials and semi- and final products) along the life cycle in the last 30 years. A total of 880 kt Nd was mined accumulatively and flowed into the global socioeconomic system, mainly as NdFeB permanent magnets (79%) in semi-products and conventional vehicles and home appliances (together 48%) in final products. Approximately 64% (i.e., 563 kt Nd) of all the mined Nd globally were not recycled, indicating a largely untapped potential of recycling in securing Nd supply and an urgency to overcome the present technological and non-technical challenges. The global Nd cycle in the past three decades is characterized by different but complementary roles of different regions along the global Nd value chain: China dominates in the provision of raw materials and semi- and final products, Japan focuses on the manufacturing of magnets and electronics, and the United States and European Union show advantages in the vehicle industry. Anticipating increasing demand of Nd in emerging energy and transport technologies in the future, more coordinated efforts among different regions and increased recycling are urgently needed for ensuring both regional and global Nd supply and demand balance and a common green future.

High-Resolution Mapping of the Urban Built Environment Stocks in Beijing.

Improving our comprehension of the weight and spatial distribution of urban built environment stocks is essential for informing urban resource, waste, and environmental management, but this is often hampered by inaccuracy and inconsistency of the typology and material composition data of buildings and infrastructure. Here, we have integrated big data mining and analytics techniques and compiled a local material composition database to address these gaps, for a detailed characterization of the quantity, quality, and spatial distribution (in 500 m × 500 m grids) of the urban built environment stocks in Beijing in 2018. We found that 3621 megatons (140 ton/cap) of construction materials were accumulated in Beijing's buildings and infrastructure, equaling to 1141 Mt of embodied greenhouse gas emissions. Buildings contribute the most (63% of total, roughly half in residential and half in nonresidential) to the total stock and the subsurface stocks account for almost half. Spatially, the belts between 3 and 7 km from city center (approximately 5 t/m2) and commercial grids (approximately 8 t/m2) became the densest. Correlation analyses between material stocks and socioeconomic factors at a high resolution reveal an inverse relationship between building and road stock densities and suggest that Beijing is sacrificing skylines for space in urban expansion. Our results demonstrate that harnessing emerging big data and analytics (e.g., point of interest data and web crawling) could help realize more spatially refined characterization of built environment stocks and highlight the role of such information and urban planning in urban resource, waste, and environmental strategies.

Product and Metal Stocks Accumulation of China's Megacities: Patterns, Drivers, and Implications.

The rapid urbanization in China since the 1970s has led to an exponential growth of metal stocks (MS) in use in cities. A retrospect on the quantity, quality, and patterns of these MS is a prerequisite for projecting future metal demand, identifying urban mining potentials of metals, and informing sustainable urbanization strategies. Here, we deployed a bottom-up stock accounting method to estimate stocks of iron, copper, and aluminum embodied in 51 categories of products and infrastructure across 10 Chinese megacities from 1980 to 2016. We found that the MS in Chinese megacities had reached a level of 2.6-6.3 t/cap (on average 3.7 t/cap for iron, 58 kg/cap for copper, and 151 kg/cap for aluminum) in 2016, which still remained behind the level of western cities or potential saturation level on the country level (e.g., approximately 13 t/cap for iron). Economic development was identified as the most powerful driver for MS growth based on an IPAT decomposition analysis, indicating further increase in MS as China's urbanization and economic growth continues in the next decades. The latecomer cities should therefore explore a wide range of strategies, from urban planning to economy structure to regulations, for a transition toward more "metal-efficient" urbanization pathways.

Product, building, and infrastructure material stocks dataset for 337 Chinese cities between 1978 and 2020.

Reliable city-level product, building, and infrastructure material stocks data are essential for understanding historical material use patterns, benchmarking material efficiency, and informing future recycling potentials. However, such urban material stocks data are often limited, due primarily to unavailable, inconsistent, or noncontinuous city-level statistics. Here, we provided such an Urban Product, Building, and Infrastructure Material Stocks (UPBIMS) dataset for China, a country that has undergone a remarkable urbanization process in the past decades, by collating different official statistics and applying various gap-filling methods. This dataset contains the stock of 24 materials contained in 10 types of products, buildings, and infrastructure in all 337 prefecture-level cities in China from 1978 to 2020. This quality controlled and unified dataset is the first of its kind with such a full coverage of all prefecture-level Chinese cities and can be used in a variety of applications, for example in urban geography, industrial ecology, circular economy, and climate change mitigation. Every piece of data is tagged with its source and the dataset will be periodically updated.