714 



UNITED STATES MINERAL RESOURCES 



tains nearly 49 percent zirconium and less than 2 

 percent hafnium, is the principal source of these 

 elements. Baddeleyite (ZrOj), a commercially im- 

 portant but less abundant zirconium-rich mineral, 

 contains approximately 73 percent zirconium and 1 

 percent hafnium (Kauffman, 1956). Because of their 

 refractory nature (melting points 2550°C or great- 

 er), these minerals are useful directly as mold 

 materials for casting ferrous metals in foundries and 

 in bricks and blocks in glass furnaces. Of an esti- 

 mated total U.S. consumption in 1970 of 145,000 

 short tons of zircon concentrates, 100,000 tons was 

 for foundries, 22,000 tons for refractories, and 

 23,000 tons for other uses (Clarke, 1970). Zircon, 

 both natural and synthetic, is also used in minor 

 quantities as a gemstone. 



Zircon is processed as an industrial mineral by 

 reacting it with dolomite at high temperatures to 

 produce zirconia (zirconium dioxide, ZrOo), which 

 has a higher melting point and is less reactive than 

 zircon in some metallurgical systems. Zirconium com- 

 pounds for other uses are prepared from zirconium 

 oxide (Stamper and Chin, 1970b) . 



ZIRCONIUM AND HAFNIUM METALS 



Zirconium metal is obtained by reacting zircon 

 with coke in electric furnaces to produce zirconium 

 carbonitride, which is chlorinated to zirconium tetra- 

 chloride. The Kroll process, which involves reduction 

 of the tetrachloride by magnesium metal in an inert 

 atmosphere, is used to obtain zirconium sponge metal 

 which contains about 2 percent hafnium. Metal fabri- 

 cated from the sponge is suitable for non-nuclear 

 applications (Stamper and Chin, 1970b). 



Both zirconium and hafnium metals have excel- 

 lent structural properties and resistance to corrosion 

 at elevated temperatures, which make them particu- 

 larly useful in reactor materials in which these 

 properties are required. 



Reactor-grade zirconium and hafnium metals are 

 produced by dissolving crude zirconium tetrachlo- 

 ride, which contains some hafnium, and chemically 

 separating the hafnium from the solution. The zir- 

 conium and hafnium components are separately pro- 

 cessed to form chlorides which are reduced to metals 

 by the Kroll process. The necessity to separate the 

 zirconium and hafnium to meet the requirements for 

 reactor-grade metals arises from the different nu- 

 clear properties of the two metals. Zirconium, hav- 

 ing a low neutron absorption cross section (less than 

 0.2 barn), is useful in reactor components in which 

 minimum neutron absorption is required. Hafnium, 

 which has a relatively high neutron absorption cross 

 section (105 barns), is useful in components in which 



neutron absorption is a desired property (Weast 

 and others, 1965; Lustman and Kerze, 1955). 



USES OF ZIRCONIUM 



In addition to its principal use for structural ma- 

 terials in nuclear reactors, zirconium metal is used 

 in small quantities in camera flashbulbs to provide 

 quick ignition and longer light intensity. Zirconium 

 alloys are used for making mechanical components 

 such as heat exchangers, valves, tubing, spinnerets, 

 and crucibles for the chemical industry (Stamper 

 and Chin, 1970b). Zirconium-columbium alloys are 

 used in superconducting magnets. Zirconium com- 

 pounds are also used in ferroalloys, glazes, enamel, 

 welding rods, abrasives, pharmaceuticals, paints, 

 and water repellents, and for sandblasting. 



Zircon and zirconium metal and compounds have 

 many substitutes in their various applications. 

 Chromite and other materials are substitute mold 

 materials. Titanium oxide and tin oxide may be used 

 in place of zirconium oxide in opacifiers for ceramic 

 glazes and enamels. Other metals and alloys, such 

 as those of titanium, tantalum, and stainless steels, 

 may be used in place of zirconium metal and alloys. 

 Substitution of other materials for zirconium ma- 

 terials is based upon specific performance, price, 

 availability, and other factors. 



USES OF HAFNIUM 

 The principal use of hafnium is in the form of 

 metal, mainly for control rods for nuclear reactors. 

 A minor amount is used as an additive in alloys, and, 

 in recent years, about 15 percent of the hafnium 

 used in the United States was used as the oxide, 

 mainly for research. Hafnium has been used in elec- 

 tric light bulbs and in electrodes in X-ray tubes and 

 other electronic tubes. Numerous other uses of hafni- 

 um have been investigated (Stamper and Chin, 

 1970a) . Alternate materials for hafnium for nu- 

 clear-reactor control rods are stainless steels con- 

 taining silver, indium, cadmium, boron, and rare- 

 earth elements. 



PRODUCTION 



Zircon, the principal raw material for the extrac- 

 tion of zirconium, is available in excess of demand. 

 Zircon production is directly related to the produc- 

 tion of titanium mineral concentrates from placer 

 sand deposits. Australia, the leading producer of 

 concentrates of titaniferous sands, is also the lead- 

 ing producer of zircon concentrates. The production 

 of zirconium concentrates in recent years from five 

 nations is given in table 157. (U.S. production figures 

 are withheld to avoid disclosing individual company 

 confidential data.) Zircon production capacity in 



