The second law of thermodynamics (2LT) helps to quantify the limits as well as the resource efficiency of the circular economy (CE) in the transformation of resources, which include materials, energy, or water, into products and residues, some of which will be irreversibly lost. Furthermore, material and energy losses will also occur, as well as the residues and emissions that are generated have an environmental impact. Identifying the limits of circularity of large-scale CE systems, i.e., flowsheets, is necessary to understand the viability of the CE. With this deeper understanding, the full social, environmental, and economic sustainability can be explored. Exergy dissipation, a measure of resource consumption, material recoveries, and environmental impact indicators together provide a quantitative basis for designing a resource-efficient CE system. Unique and very large simulation models, linking up to 223 detailed modeled unit operations, over 860 flows and 30 elements, and all associated compounds, apply this thermoeconomic (exergy-based) methodology showing (i) the resource efficiency limits, in terms of material losses and exergy dissipation of the CdTe photovoltaic (PV) module CE system (i.e., from ore to metal production, PV module production, and end-of-life recycling of the original metal into the system again) and (ii) the analysis of the zinc processing subsystem of the CdTe PV system, for which the material recovery, resource consumption, and environmental impacts of different processing routes were evaluated, and the most resource-efficient alternative to minimize the residue production during zinc production was selected. This study also quantifies the key role that metallurgy plays in enabling sustainability. Therefore, it highlights the criticality of the metallurgical infrastructure to the CE, above and beyond simply focusing on the criticality of the elements.
