World nonbauxite aluminum resources excluding alunite

Abstract

The nonbauxite resources having the best potential for extraction of aluminum are alunite, high-alumina clay, and aluminous igneous rocks; those having less potential are dawsonite-bearing rocks, aluminous phosphate rocks, saprolite, aluminous metamorphic rocks, aluminous shale, coal waste, and coal ash. With the exception of alunite, which was discussed in the separately published Chapter A of this Profes sional Paper, all these resources are discussed in this report. The high-alumina clays are composed of minerals of the kaolin group-kaolinite, halloysite, dickite, and nacrite. Kaolinite is by far the most abundant, and it is the major component in a variety of highalumina clays. High-alumina clays have a maximum alumina content of about 39 weight percent. However, no large deposits are pure, and most high-alumina clay deposits are 25-35 weight percent alumina. Igneous rocks exceptionally rich in alumina include anorthosite, nepheline syenite, phonolite, and leucite-bearing volcanic rocks. U.S. anorthosite contains 24-33 weight percent alumina, U.S. nepheline syenite contains 17-23 weight percent alumina, and Italian leucitebearing rocks contain 20-22 weight percent alumina. The mineral dawsonite, which contains 35.4 weight percent alumina, occurs in oil shale but makes up no more than 12-25 weight percent of the rock. Therefore, any aluminum production from dawsonite must depend upon other products from the shale such as oil and soda ash derived from nahcolite. The aluminous phosphate rock associated with phosphate deposits is the result of calcium phosphate being leached by meteoric waters. The alumina content of such phosphate rock in the United States ranges from about 6 to 15 weight percent, and the aluminum phosphate minerals make up 20-30 weight percent of the rock. Any aluminum production from this rock will depend on the recovery of other products such as phosphate and uranium. The Thies region, Senegal, is the only place in the world where significant tonnages of aluminum phosphate are mined. Saprolite is a decomposed rock formed in place by subaerial chemical weathering of any kind of rock; it retains the original structure and texture of the parent rock. Some saprolite is similar in chemical and mineral composition to high-alumina clay, and some saprolite contains gibbsite replacing kaolinite. Generally, saprolite that is a potential resource of alumina contains 20-38 weight percent alumina. Aluminous metamorphic rocks contain the minerals kyanite, sillimanite, andalusite, topaz, or dumortierite. These minerals contain 55-64 Manuscript approved for publication, November 3, 1989. weight percent alumina. Aluminous metamorphic rocks may contain as much as 40 weight percent kyanite-group minerals, but generally they contain less than 15 weight percent. Aluminous shales are sedimentary rocks formed by the consolidation of clay-and silt-sized material. Almost all shales contain some quartz and the clay minerals illite, kaolinite, and (or) smectite. The alumina content of shale that is a potential resource...

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