- Bauxite forms a vast majority of the mineral markets and is shipped directly to consuming plants as mined or minimally pre-processed. This is true for bauxite from Jamaica and elsewhere including the US where they are shipped far distances for conversion into various products, most of which employ the rotary kiln.
- The main uses of bauxite include the manufacture of metallic aluminum and aluminous chemicals, aluminous abrasives, and aluminous refractories. In the manufacture of metallic aluminum, the bauxite is first purified by chemical methods and the resultant product, aluminum hydrate, is calcined to produce aluminum oxide or alumina. For refractory grades they are calcined to remove bound moisture at temperatures around 1500 C (2700 F). Bauxite/Kaolin – Al2O3.2SiO2.2H2O (40:46:14 wt% ratios) are calcined and used widely in paints, fillers, etc. Some of the heat of formations for the reactions of Al2O3 to a-alumina and g-alumina are presented in Table A.13.
- Rotary kiln produced aluminous chemicals from bauxite include aluminum sulfate and its derivatives, the alums, aluminum hydrate, aluminum chloride, and sodium aluminate. Aluminum sulfate is produced by treatment of bauxite or aluminum hydrate with sulfuric acid. Aluminum hydrate and sodium aluminate result from treatment of bauxite with caustic soda. Sodium aluminum sulfate, NaAl(SO4)2.12H2O or Na2SO4.Al2(SO4)3.24H2O, also known as soda alum, is used as acidity regulator of food in the manufacture of baking powder and is calcined using short L/D rotary kilns. Some feedstocks can be produced on site as part of the overall kiln process. Budenheim Chemicals operate plants around the world including in the US and the kiln feedstock is prepared on site.
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