It always occurs with hafnium, which has almost identical chemical properties. Fla. The metal is produced by the Kroll process. The zircon is treated with carbon in an electric furnace to form a cyanonitride, which is in turn treated with chlorine gas to form the volatile tetrachloride. The tetrachloride is carefully purified by sublimation in an inert atmosphere and is then chemically reduced to metal sponge by reaction with molten magnesium. The spongy metal is cleaned and further processed into ingots.
Special care is taken to exclude hydrogen, nitrogen, and oxygen, which make the metal brittle.
If the metal is too brittle to be worked, it can be further purified by the Van Arkel-de Boer process, in which the crude metal is reacted with iodine to form volatile iodides that are thermally decomposed on a hot wire, resulting in pure crystalline zirconium. Zirconium was discovered as the oxide zirconia in the mineral zircon by M. H. Klaproth in 1789 and was first isolated in impure form by J. J. Berzelius in 1824. Listing from Electric Library , a pay service. No relevant pictures or maps found. The Columbia Electronic Encyclopedia, Sixth Edition Copyright 2000, Columbia University Press.