Bureau of Mines / Minerals yearbook: Metals and minerals 1978-79
Year 1978-79, Volume 1 (1978-1979)
Potter, Michael J.
Kyanite and related materials, pp. 503-506 PDF (439.3 KB)
503Kyanite and Related Materials By Michael J. Potter' Kyanite, andalusite, and sillimanite are anhydrous aluminum silicate minerals that are alike in both composition and use patterns and have the same chemical formula, A1203*Si02. Related materials include synthetic mullite, dumortierite, and topaz, also classified as aluminum silicates, although the last two additionally contain substantial proportions of boron and fluorine, respectively. All of these kyanite-group substances can serve as raw materials for manufacturing special high-performance, high-alumina refräctories, but there has been no record in recent years of significant utilization of either dumortierite or topaz for this purpose in the United States. Although published statistics are incomplete, it appears that the United States, India, and the Republic of South Africa are the leading world producers of kyanitegroup minerals. It can be presumed that the U.S.S.R. and perhaps a few other industrialized nations also produce significant quanti ties of these materials. U.S. kyanite estimated production in both 1978 and 1979 increased slightly in tonnage and value. Export and import data since 1977 for kyanite and mullite-containing materials are no longer collected as a separate category by the Bureau of the Census. NL Industries, Inc., announced in late 1978 the sale of its Taylor Refractories Division to Didier Werke of Wiesbaden, Federal Republic of Germany. The sale of the division and related assets amounted to approximately $32 million. Taylor produces mullite and other special refractories, plus a wide range of kiln furniture, shapes, bricks, and monolithic refractories, mainly based on nonbasic materials. Legislation and Government Programs.—The allowable depletion rates for kyanite, established by the Tax Reform Act of 1969 and unchanged through 1979, were 22% for domestic production and 14% for foreign operations. DOMESTIC PRODUCTION Kyanite was produced in the United States in 1978 and 1979 at three open pit mines, two in Virginia and one in Georgia. Kyanite Mining Corp. operated the Willis Mountain and East Ridge mines in Buckingham County, Va. C-E Minerals, Inc., operated the' Graves Mountain mine in Lincoln County, Ga. Estimated output of domestic kyanite in both 1978 and 1979 showed slight increases in tonnage and value. Kyanite production statistics for 1979 (and for all previous years since 1949) are withheld to avoid disclosing company proprietary data. There are three types of synthetic mullite. Fused synthetic mullite is made by melting Bayer process alumina and silica, or bauxite and kaolin, in an electric furnace at around 3,450'F. High-temperature sin- tered synthetic mullite is prepared by sintering mixtures of alumina and kaolin, bauxite and kaolin, or alumina, kaolin, and kyanite above 3,180*F. Low-temperature sintered synthetic mullite is made by sintering siliceous bauxite or mixtures of bauxite and kaolin above 2,820*F. Output of synthetic mullite in 1978 and 1979 was largely of the high-temperature sintered variety, and the four producers of this material were A. P. Green Refractories Co. at Philadelphia, Pa.; C-E Minerals, Inc., at Americus, Ga.; Didier Taylor Refractories Corp. at Greenup, KY.; and HarbisonWalker Refractories Co. at Eufala, Ala. Electric-furnace-fused mullite was produced by Muscle Shoals, Electrochemical Div., at Tuscumbia, Ala. (in 1978), and The Carborundum Co. at Niagara Falls, N.Y.
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