Shifts and trends in the global anthropogenic stocks and flows of tantalum

•Global anthropogenic tantalum cycles have been developed for the years 1970-2015.•Tantalum's EoL-RR seems to have declined from a high of 25% in the 1990s to 18% today.•Only 21-25% of tantalum produced since 1970 is still in use, mainly in capacitors.

The supply and demand of tantalum has undergone a number of significant shifts over the past few decades. The purpose of this work is to quantify how these shifts have affected tantalum's global material cycle. A global stocks and flows model for tantalum has thus been developed for the years 1970-2015. The results indicate that the overall quantity of tantalum prompt scrap generated during manufacturing has increased notably due to tantalum's increased use as an alloy additive and sputtering target. In contrast, the amount of tantalum contained in recycled obsolete scrap, mainly in the form of used carbides, is estimated to have remained relatively constant since the late-1980s. Moreover, tantalum's overall end-of-life recycling rate (EoL-RR) seems to have declined from a high of 22-25% in the 1990s to approximately 18% today. This decline is also attributable to the shift in tantalum's use from carbides to sputtering targets and chemicals that, along with tantalum's use in capacitors, have not been recycled at the end-of-life (EoL) in significant quantities. The results also indicate that 21-25% of tantalum produced since 1970 is still in use today, with the remainder having been lost during processing, manufacturing, use, or at the EoL. However, a portion of the EoL “discards” may actually still be retained by the end-user as “hibernating” stocks that could potentially be recycled if the economic, technical, and behavioral challenges of recycling obsolete electronics are overcome.