Recycling metals

Extractive industries, such as mining, are inherently unsustainable, because the crust of the Earth contains only a finite supply of metals.  In my younger days of field work in the Southwest, I was appalled at the environmental scars of mining in the desert environment.  Often I thought there must be a better way to reduce this impact.

Modern society recycles a fair percentage of its annual use of metals, such as iron, lead, copper, and zinc, but inevitably some supplies are dissipated into the environment, like the lead in shotgun shells.  Some materials are incorporated into long-lived products, like steel girders in high-rise construction, and much of the demand for gold is driven by long-term possession.

One must expect that with rising human population new (virgin) sources of ore will be mined to satisfy the demand for more products. There is also new demand for some materials, such as lithium, cobalt, and rare earth elements, to supply the electronics and battery industries.

Alexandre Poncelet and colleagues have recently attempted to estimate the average lifetime of metals in the global economy to evaluate the extent of recycling.  They define lifetime as the amount of a metal in current use globally, divided by its loss to the environment in dissipated and discarded products. The values range from 192 years for gold to 10 years or less for a wide variety of elements, including rare earths, that are not effectively recycled.  Iron and lead, which have well established traditions of recycling, have lifetimes of 154 and 27 years, respectively, in the economy. One might expect that the average lifetime of lithium in the economy, about 7 years, will increase as programs emerge to recycle lithium batteries.  A similar expectation should accompany cadmium, arsenic, and tellurium which are used in solar panels, most of which are still in their initial round of service.

The lifetime of metals that are toxic to organisms including humans is of particular interest, since it would behoove us to recover as much of these materials as possible.  Here, mercury (lifetime = 5 years), arsenic (2 years) and cadmium (8 years) deserve special attention.  There are considerable inadvertent losses of mercury and arsenic to the environment during the extraction of other metals (viz. gold and copper), especially as the availability of high-grade ores declines.

As long as human population is rising, we will never stop mining metals from the Earth’s crust. There are powerful reasons to promote recycling as a path to a healthy and sustainable biosphere.  As the cost of metals rises, so too will the motivation to recycle them.  This will help ensure that no metal goes to a landfill.

 

References

Graedel, T.W. 2018.  Grand challenges in metal life cycles. Natural Resources Research 27: 181-190.

Poncelet, A.C. and 9 others. 2022.  Losses and lifetimes of metals in the economy.   Nature Sustainability 5: 717-726.

Schlesinger, W.H., E.M. Klein, Z. Wang and A. Vengosh. 2021.  Global biogeochemical cycle of lithium.  Global Biogeochemical Cycles   doi:10.1029/2021GB006999

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