The PGM Dilemma

What are PGMs, you ask? They are platinum group metals. There are six of them—ruthenium, rhodium, palladium, osmium, iridium, and platinum. They are noble metals—highly resistant to corrosion, acids, and decomposition. Like gold, they are also very rare—the rarest and least abundant stable metals in the Earth’s crust. Here they are listed in milligrams per kilogram (below right). Below,...