The assessment of the criticality of raw materials allows the identification of the likelihood of a supply disruption of a material and the vulnerability of a system (e.g. a national economy, technology, or company) to this disruption. Inconclusive outcomes of various studies suggest that criticality assessments would benefit from the identification of best practices. To prepare the field for such guidance, this paper aims to clarify the mechanisms that affect methodological choices which influence the results of a study. This is achieved via literature review and round table discussions among international experts. The paper demonstrates that criticality studies are divergent in the system under study, the anticipated risk, the purpose of the study, and material selection. These differences in goal and scope naturally result in different choices regarding indicator selection, the required level of aggregation as well as the subsequent choice of aggregation method, and the need for a threshold value. However, this link is often weak, which suggests a lack of understanding of cause-and-effect mechanisms of indicators and outcomes. Data availability is a key factor that limits the evaluation of criticality. Furthermore, data quality, including both data uncertainty and data representativeness, is rarely addressed in the interpretation and communication of results. Clear guidance in the formulation of goals and scopes of criticality studies, the selection of adequate indicators and aggregation methods, and the interpretation of the outcomes, are important initial steps in improving the quality of criticality assessments.

Society requires a stable and secure supply of raw materials. Raw materials supply stability and security are, amongst others, addressed by the concept of raw materials criticality, which focuses on the vulnerability of an economic unit (most commonly a country or region, but also the world, specific sectors, companies or products) to supply restrictions of certain mineral raw materials (cf. Schrijvers et al., 2020). The idea of keeping materials in the economic cycle for longer is specified in the Circular Economy (CE) concept, which encompasses efforts that reduce waste and improve material efficiency (Ellen McArthur Foundation, 2013; European Commission, 2018). So far, CE beyond recycling has not played a prominent role in the criticality debate. At the same time, critical raw materials (CRM) have only been a minor topic in the discussion on CE (recent exceptions include European Commission, 2018, and Gaustad et al., 2018). If properly aligned, criticality assessments might help in defining priority materials for the CE, and circularity strategies could substantially mitigate supply risks. In this paper, we explore the potential benefits, as well as caveats, of adopting a CE approach to CRM, based on our own experiences and our discussions organized by the IRTC (International Round Table on Materials Criticality) project.