A crustal scarcity indicator for long-term global elemental resource assessment in LCA

Purpose How to assess impacts of mineral resources is much discussed in life cycle assessment (LCA). We see a need for, and a lack of, a mineral resource impact assessment method that captures the perspective of long-term global scarcity of elements. Method A midpoint-level mineral resource impact assessment method matching this perspective is proposed, called the crustal scarcity indicator (CSI), with characterization factors called crustal scarcity potentials (CSPs) measured as kg silicon equivalents per kg element. They are based on crustal concentrations, which have been suggested to correlate with several important resource metrics (reserves, reserve base, reserves plus cumulative production, and ore deposits), thereby constituting proxies for long-term global elemental scarcity. Results and discussion Ready-to-use CSPs are provided for 76 elements, through which the CSI can be calculated by multiplying with the respective masses of elements extracted from Earth's crust for a certain product. As follows from their crustal concentrations, the three platinum-group metals iridium, osmium, and rhodium have the highest CSPs, whereas silicon, aluminum, and iron have the lowest CSPs. Conclusion An evaluation of the CSPs and the characterization factors of four other mineral resource impact assessment methods in LCA (the abiotic depletion, the surplus ore, the cumulative exergy demand, and the EPS methods) were conducted. It showed that the CSPs are temporally reliable, calculated in a consistent way, and have a high coverage of elements in comparison. Furthermore, a quantitative comparison with the characterization factors of the four other methods showed that the CSPs reflect long-term global elemental scarcity comparatively well while requiring a minimum of assumptions and input parameters. Recommendations We recommend using the CSI for assessments of long-term global elemental scarcity in LCA. Since the CSI is at the midpoint level, it can be complemented by other mineral resource impact assessment methods (both existing and to be developed) to provide a more comprehensive view of mineral resource impacts in an LCA.