One morning in September, a truck disgorged its load of pulverized rock with a resounding bang inside Stillwater Mining’s metallurgical plant north of Yellowstone National Park. The mined ore contains platinum, palladium and rhodium, three of the earth’s rarest, most expensive metals — and vital components in the millions of catalytic converters that reduce polluting emissions from gasoline-powered vehicles. At the opposite end of the plant was another batch of metal, not from the mine but from used catalytic converters ground into powder for recycling. The new and the old metals would later be blended under intense heat, then shipped to a refinery. Recycling catalytic converters costs less than mining the ore.

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Locations: Yellowstone, Stillwater