Modern innovative products tend to utilize a broad range of elements because each element has a unique fundamental property. (1) Magnetism is one of the major properties needed for clean energy technologies (e.g., power electric vehicles). Dysprosium (Dy), a rare-earth element, is effective in ensuring the magnetic strength of the most widely used magnet, neodymium–iron–boron (Nd–Fe–B). (2,3) Thus, the transition to clean energy is projected to be accompanied by an exponential increase in Dy demands. (4) However, only a few regions have provided Dy-bearing mineral resources in the last three decades. Approximately, 90% of minerals were produced by China and Burma in 2018 (Figure S1). Due to the growing demand and supply risk, Dy availability has received considerable attention. (4,5) Particularly in the United States (US), Dy has been regarded as a critical raw material since early 2012. (6) A recent study enhanced concerns about Dy supplies in the US because of the difficulty in recovering and reusing it. (7) Particularly in this post-pandemic period, supply risks are amplified by trade policy changes and suspended operations. Since 2009, throughout the globe, governments, companies, and research institutes have taken actions to minimize the potential impact of Dy shortage, (8) for example, by supporting the development of low-Dy Nd–Fe–B magnets by the Japanese government (9) and the recycling of Dy-bearing secondary resources by the European Commission. (10)

Exploring Dy flows between products and across countries is essential to devise strategic plans. Some researchers attempted to identify and quantify the major factors that contribute to the US Dy availability and supply risks, (11–13) such as the depletion time of domestic reserves, country concentration, and governance, and they primarily focus on Dy ore supply. Several other studies evaluated Dy demands for finished products under specific scenarios, such as for wind turbines driven by the Wind Vision Project (14) and Blue Map (15), and electric vehicles by automotive electrification, (16,17) which informed the decision-makers of potential material-related issues in particular initiatives. (18–23) Furthermore, several studies were conducted to identify particular sources of certain products (e.g., domestic extraction of ores, (24) cross-border trade of alloys (8,20,25), and finished products (23,26)). Owing to scarce data, element-specific material flow analysis (MFA) of rare-earth elements in the US has not been conducted, and information on domestic demands for Dy-bearing chemicals and alloys is unavailable. Element-specific information is crucial for making decisions on capacity planning (business level), industrial development (industry level), and national strategy formulation (country level). One such example is the volume of national strategic stockpiles (mostly composed of chemicals) determined according to the demands of manufacturing industries. So far, the information about Dy flows is still incomplete.

Thus, to bridge the knowledge gap related to the US Dy, we performed a dynamic MFA covering the period from 1987 to 2018. The MFA has been used as an effective tool to explore material flows into, out of, and within a certain system by analyzing material production, consumption, and international trade from a lifecycle perspective. (27,28) Notably, in this study, we explored the comprehensive coverage of products, processes, and periods. First, the MFA framework adopted in our study considers all types of Dy-bearing products available in the US market including ores, concentrates, chemicals, alloys, and finished products. Second, it distinguishes the US from the rest of the world, allowing for comparative analyses of domestic and overseas supply and demand. Third, it explores the scenario starting from 1987, when the first Dy chemicals were produced by factories in the US. The results reveal the temporal evolutions of the whole Dy supply chain as well as the causes and consequences and provide quantitative information on the Dy flows in the US. Based on these results, the progress of actions and policies, as well as near-term implications, are discussed...

Figure 2. Cumulative Dy flows in the US from 1987–2018. Values are measured using the metallic equivalent weight (in metric ton Dy). According to the mass-balance principle, the domestic demands for the upstream products equal domestic supplies for the downstream industries. For example, the domestic demand for concentrates drives compound production. According to the results of the uncertainty analysis, the total domestic demand for finished products is likely to range from 6200 to 11,000 t Dy, with a 97.5% confidence.

Figure 3. Dy demand (measured in t Dy) in percentage. (A) Average, (B) by years and amounts, and (C) for finished products.

Figure 4. Total supplies (i.e., domestic production plus imports), import dependency, and demands (i.e., domestic consumption plus exports) of (a) concentrates, (b) chemicals, (c) alloys, and (d) finished products. Consumption is represented by the domestic production of downstream industries.