High grade zirconium

Two principal solvent-extraction methods are used for the production of high-grade zirconium, based upon the solvents hexone (methyl-isobutyl-ketone) and tributyl phosphate. In both cases, the aim is to purify the zirconium from its chemical homologue, hafnium, but in some variants of the process the other metallic impurities are also removed. It is also possible to obtain the hafnium in a pure condition if required, and to obtain fairly good yields of both zirconium and hafnium. 

Because of its low neutron-capture cross-section and high resistance to corrosion, the manufacture of high-grade zirconium, free from hafnium, has been developed to a great extent in the U.S.A. for use in pressurized water reactors. 

It is used for the production (thermal reduction) of other metals, such as zinc, iron, titanium, zirconium, and nickel. For instance, because of its strong electropositive nature, magnesium can desulfurize molten iron when it combines with the sulfur impurities in the iron to produce high-grade metallic iron plus MgS. 

Hafnium is obtained as a by-product of the production of hafnium-free nuclear-grade zirconium (see Nuclear reactors ZlRCONlUMAND zirconium compounds). Hafnium s primary use is as a minor strengthening agent in high temperature nickel-base superalloys. Additionally, hafnium is used as a neutron-absorber material, primarily in the form of control rods in nuclear reactors. 

Bingen B., Austrheim H., and Whitehouse M. (2001) Ilmenite as a source of zirconium during high-grade metamorphism Textural evidence from the Caledonides of western Norway and implications for zircon geochronology. J. Petrol. 42, 355-375. 

Fraser G., Ellis D., and Eggins S. (1997) Zirconium abundance in granulite-facies minerals, with implications for zircon geochronology in high-grade rocks. Geology 25, 607-610. 

This industry has most of the corrosion problems of other industries and some that are all of its own. Right from the start, the potential for disaster was recognized and tackled by using high-grade materials in many parts of the systems. Zirconium alloys were needed, which had their own corrosion problems and solutions. Growing worldwide demands for acceptable environmental performance have alienated others to the cause of nuclear power, in particular, after events at Three Mile Island and Chernobyl. 

Although the solvent purification process is adequate for the production of say reactor-grade zirconium, it is possible to modify it so that pure hafnium may also be obtained. Distribution data are available for various solutions containing thiocyanate, sulphate and chloride from which it is possible, for example, to deduce that both hafnium and zirconium will extract into hexone provided the aqueous phase has a high thiocyanate concentration and a low chloride concentration. The zirconium may then be selectively backwashed in a second extractor using say an aqueous phase of high thiocyanate concentration and moderate sulphate concentration, where the separation factor of the system is high. The hafnium can then... 

As it occurs in nature, zirconium is always found in association with hafnium, in the ratio of 1 part hafnium to 50 parts zirconium, and commercial-grade zirconium contains approximately 2% hafiiium. Because hafnium has a high absorption capacity for thermal neutrons, nuclear reactor-grade zirconium is not permitted to contain more than 0.025% Hf, and usually it contains closer to 0.01%. 

Iodine is used in many dyes and as a colorant for foods and cosmetics. Its silver salt is used in photographic negative emulsions. Other industrial applications include dehydrogenation of butane and butylenes to 1,3-butadiene as a catalyst in many organic reactions in treatment of naphtha to yield high octane motor fuel and in preparation of many metals in high purity grade, such as titanium, zirconium and hafnium. 

The pnrity of qnartz sand required for the manufacture of soluble silicate has to be high, for example, the iron content should not exceed 300 ppm [7,11,41]. The primary contaminant is Ec203, followed by titanium oxide (rutile), zirconium oxide, and chromium oxide. Typical analysis data of high-quality grades are Si02 ca. 99.0-99.8%, Fe203 ca. 0.01-0.05%, and AI2O3 ca. 0.05-0.5% [40]. 

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