Thorium - Th
Thorium was discovered in 1829 by J.J. Berzelius in Stockholm. Thorium is a dark grey, radioactive metal of which the principal source is the ore, monazite, a complex phosphate of thorium, uranium, cerium and lanthanides. The metal is soft and ductile and is extracted by precipitation as the hydroxide, along with cerium and uranium; separation is achieved by further extraction with tributyl phosphate from an acid solution. The metal is made by calcium reduction of the oxide or fluoride, and pure thorium can be obtained by decomposing ThI₄ on a hot filament (the Van Arkel process). Thorium is used as an alternative reactor fuel to uranium, thorium being converted readily into uranium in the reactor. Thorium is extremely efficient as an energy source, the earthly reserves of thorium containing more energy than all other fossil fuel sources combined.