Per this article in Scientific American, which was written based on a publication in the Proceedings of the National Academy of Sciences USA: - " Daniel MÃ¼ller of Yale University and his colleagues derived the first estimates of the total stock of iron in use and elsewhere in the U.S." They have estimated "that between 1900 and 2004 the U.S. has brought into use 3.2 billion metric tons of iron." Reminding us of an earlier post on copper sustainability, the authors concluded that what exists, as iron in product, is similar to the amount of iron left in the ground as ore. Notably, the remaining ore in North America is generally of lower grade than what was historically mined and smelted, and therefore will only be reduced to iron at a relatively higher cost in energy and C02 emissions. The report also states that "U.S. per capita demand for steel has stabilized at roughly 12 metric tons since 1980..." While "77 million metric tons of iron leave use every year, only 57 million metric tons reach the recycling stage (and only 42 million metric tons make it back into use)".
Did the mass balance account for ships long ago made in the US, and now headed for the scrap heap in India? What of sunken war ships from WWII? Particularly disturbing is that the US-based Iron and Steel Institute reports an overall recycling rate for steel of 70.7 percent in the year 2002. It would be convenient to just assume the common sense explanation that 'in the olden days scrap was mostly thrown out and steel beer cans left to rust in the fields', and that the short term modern recycle rate for steel is indeed 70+ percent, leaving the long term average, represented quited reasonably, closer to 54% (calculated by this author from the cited numbers). Perhaps the important point is that 70% is nowhere good enough for society already into the Peak Iron phase of resource consumption.
Photo credit: Scientific American