Illuminating tungsten's life cycle in the United States: 1975-2000.
Tungsten's unique properties, such as its high density and melting point, are manifest in a variety of technological applications, and attention has recently centered upon the health and environmental effects of tungsten. Utilizing material flow analysis, the amounts of tungsten produced, fabricated and manufactured, entering use, and entering waste management in the United States from 1975-2000 were determined, with the inclusion of net trade, and with attention paid to the way that tungsten partitions into in-use reservoirs and the quantities of tungsten that enter the environment as a result of anthropogenic processes. The results from two approaches are presented: the first and typical, approach for historical material flow analysis studies, whereby tungsten use in products over time was approximated using end-use sectors used by the United States Bureau of Mines and the United States Geological Survey (the "end-use sector model") and a second, more detailed approach whereby the historical pattern of end-use products was determined (the "finished product model"). These models represent the first life cycle of tungsten that takes into account both finished product trade and varying residence times for products entering use. For the cumulative time period of 1975-2000, approximately 60% of the supply to fabrication and manufacturing processes in the United States consisted of imports. The tungsten embodied in products used in applications other than transportation is discarded (i.e., enters the waste stream, which encompasses both material that is eventually landfilled and that is eventually recycled) in the same year it enters service. Of its items entering end-of-life for the cumulative time period, 50-70% of tungsten is estimated to be landfilled. In both models, the largest flows of tungsten to the environment were estimated to originate from post-consumer discards. Approximately 8-17 times as much tungsten entered landfills than was estimated to be generated as waste from fabrication and manufacturing processes; for tailings, these ratios are even greater. Tungsten is an example of a critical mineral resource where the majority of the United States' supply comes from imports, it has vital uses in manufacturing, and it has a high rate of loss at end-of-life.
Harper
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EM
Center for Industrial Ecology, School of Forestry and Environmental Studies, 205 Prospect Street, Yale University, New Haven, Connecticut 06511, USA. erm_harper@yahoo.com
Graedel
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TE
D014414:Tungsten / Q000737:chemistry*; D014481:United States
D014414:Tungsten