Substance flow analysis of copper in production stage in the U.S. from 1974 to 2012

Substance flow analysis (SFA) provides a systematic framework for tracking the sources, pathway, intermediate and final sinks of copper in the United States. The stocks and flows (STAF) method compensates for the deficiency in statistics. This paper combines SFA and STAF method to reflect the realistic copper stocks and flows within production boundary from 1974 to 2012. The goal of this paper is to discern the evolution of the copper production industry in the U.S. when conditions require that industry operates with a lower-grade ore and more sustainable development concerns are considered. The emergence of the new solvent-extraction electrowinning (SX-EW) technology, which is used in conjunction with conventional extractive metallurgy, altered the structure of domestic refined copper production. Refined copper production declined after peaking at 2486 Gg/year in 1998. In 2012, primary production was only 45.02% of the primary production in 1998, and secondary production was only 10.69% of secondary production in 1998. The decrease is due to the decline in the primary and secondary copper sources for domestic use and closure of secondary smelting and refining facilities. A portion of the lower grade ore was exported through trade after 1998. More scrap was not delivered to produce refined copper. Closure of secondary smelting and refining facilities decreased the refinery scrap in a poor economic environment. Imported refined copper offset the gap due to the decrease in domestic refined copper production. The ratio of net imported refined copper to domestic refined copper increased from 9.97% in 1974 to 47.03% in 2012. The U.S. is more dependent on import of refined copper, except during the period in which a tight global copper market disrupted the leading copper-producing country.