Tracking the devil's metal: Historical global and contemporary U.S. tin cycles

Tin is an essential industrial metal with many applications from plastics to electronics. In contrast to other metals, tin reserves are very small with a static lifetime of 22 years. Mining is heavily concentrated in a few countries. Together, these characteristics render primary tin supply potentially vulnerable to short and long-term disruptions. An increased use of secondary tin resources (e.g., scrap from retiring products) could replace primary tin and thereby mitigate both challenges. In order to identify the potential for secondary resource use, it is necessary to know both where tin is accumulating in the anthroposphere and where tin could be recovered most effectively. We first analyzed the global, historical tin metabolism on a highly aggregated level to identify areas of stock accumulation. Subsequently, we studied the contemporary (2005) U.S. tin cycle in more detail to detect flows rich in tin for potential recycling. Most of the tin mined globally in the 20th century has been accumulating in landfills due to a relatively short lifetime and low recovery rates. The global tin reservoir in landfills has reached about double the size of current reserves, while products in use constitute about half the amount in reserves. In addition, substantial amounts of tin have accumulated in steel (where it forms a tramp element and is virtually lost for future recovery). Landfills might become important tin mines in the future, however, currently more attractive is a focus on in-use stocks, where tin is available in higher concentrations. Today, the U.S. has a post-consumer recycling rate of about 28%, exclusively in alloy form. The most important current source of post-consumer recycled material is lead acid batteries. Products that are good candidates for improved end of life recycling include containers and electronics, although this potential is not currently being harvested in the U.S.