Assessment of the Secondary Copper Reserves of Nations.

The sustainable use of metals demands consideration not only of primary metals in the natural environment but also of secondary metals in society as alternative resources. This study applied our proposed classification framework of secondary resources to copper (1) to investigate the applicability of the framework and (2) to assess the secondary copper reserves and resources of selected countries. To estimate secondary copper reserves, we introduced the variable "secondary reserve ratio": the fraction of in-use copper stocks that is technically and economically recoverable. Our estimates showed that the United States and China have secondary copper reserves of 44 and 33 Mt, respectively, and showed that global secondary copper reserves are about 30% of global primary reserves. The application of the classification framework showed that considerable amounts of secondary copper resources are in landfills, which are potential targets of future extraction of secondary copper through landfill mining. Overall, the classification framework provides a better understanding of the current size of available secondary resources and waste deposits. It also highlights the need for integrated management of primary and secondary resources.