Classifying urban mineral resources and reserves for a circular economy

Humans have changed planetary boundaries; the depletion of virgin minerals and accumulation of urban minerals are occurring. In contrast to geological resources, the scientific classification of anthropogenic resources remains unsolved. Clarifying where, when, how many, and how various urban minerals accumulate and can be extracted is crucial for fostering a circular economy material "closed loop". To this end, we developed a structural and evidence-based quantifiable classification method to explore the availability (resource) and accessibility (reserve) of urban minerals. Using China's electric and electronic equipment and automobile industries as a case study, our analysis indicates that the annual urban minerals "formation" in 2023 has reached 27 million tons. Among 42 target metals, eight were mineable, 26 were unmineable, and the remaining eight were swinging between mineable and unmineable across scenarios. Furthermore, we found that enhancing separation and recovery ratios for Fe, Al, Cu, and precious metals can further reduce reliance on natural sources for these minerals by 9%-15% and that optimizing recycling value thresholds for the other 37 metals (e.g., rare earth elements and light metals) can replace the need to mine 7%-42% of these virgin minerals, potentially raising present circularity of electrical and electronic equipment and automobiles from one-third to half. This study reveals the "availability-accessibility" gradient structure of urban minerals and its coupling across policy, technological, and economic dimensions, offering scientific support for building urban mineral databases, formulating urban mining policies, and promoting the implementation of urban mining.