This study seeks to understand the role of primary processing, i.e. the first post-mining stage, in supply risk, by means of a case study on three critical metals (neodymium, cobalt, and platinum) in the context of Japan. Applying the ‘footprint’ concept with a multiregional input–output model, we have quantified the direct and indirect vulnerability of the Japanese economy to such risks. Considering the supply risks associated with primary processors, we find that Japanese final consumers are exposed to relatively higher supply risks for neodymium as compared with cobalt and platinum. Our study shows that the primary processing stage of a metal’s supply chain may contribute significantly to the overall supply risks, suggesting that this stage should be taken into due account in understanding and mitigating supply-chain vulnerability through, e.g. supplier diversification and alternative material development.

This study, encompassing 231 countries and regions, quantifies the global transfer of three critical metals (neodymium, cobalt, and platinum) considered vital for low-carbon technologies by means of material flow analysis (MFA), using trade data (BACI) and the metal contents of trade commodities, resolving the optimization problem to ensure the material balance of the metals within each country and region. The study shows that in 2005 international trade led to global flows of 18.6 kt of neodymium, 154 kt of cobalt, and 402 t of platinum and identifies the main commodities and top 50 bilateral trade links embodying these metals. To explore the issue of consumption efficiency, the flows were characterized according to the technological level of each country or region and divided into three types: green ("efficient use"), yellow ("moderately efficient use"), and red ("inefficient use"). On this basis, the shares of green, yellow, and red flows in the aggregate global flow of Nd were found to be 1.2%, 98%, and 1.2%, respectively. For Co, the respective figures are 53%, 28%, and 19%, and for Pt 15%, 84%, and 0.87%. Furthermore, a simple indicator focusing on the composition of the three colored flows for each commodity was developed to identify trade commodities that should be prioritized for urgent technical improvement to reduce wasteful use of the metals. Based on the indicator, we discuss logical, strategic identification of the responsibilities and roles of the countries involved in the global flows.