Processing of low-quality bauxite feedstock by thermochemistry-Bayer method
- 1 — Ph.D., Dr.Sci. professor Saint-Petersburg Mining University
- 2 — Ph.D., Dr.Sci. professor Norilsk Nickel Harjavalta Oy
Abstract
The modern production of aluminum which by its global output ranks first among the non-ferrous metals includes three main stages: ore extraction, its processing into alumina and, finally, the production of primary aluminum. Alumina production from bauxites, being the primary raw material in the alumina industry, is based on two main methods: the Bayer method and the sintering method developed in Russia under the lead of an academician Nikolay Semenovich Kurnakov. Alumina production by the Bayer’s method is more cost effective, but has higher requirements to the quality of the bauxite feedstock. A great deal of research has been carried out on low quality bauxites focusing firstly on finding ways to enrich the feedstock, secondly on improving the combined sequential Bayer-sintering method and thirdly on developing new hydrometallurgical ways for bauxites processing. Mechanical methods of bauxite enrichment have not yet brought any positive outcome, and a development of new hydrometallurgical high alkaline autoclave process faced significant hardware difficulties not addressed so far. For efficient processing of such low quality bauxite feedstock it is suggested to use a universal thermochemistry-Bayer method, which was developed in St. Petersburg Mining University under the lead of Nikolay Ivanovich Eremin, allows to process different substandard bauxite feedstock and has a competitive costing as compared to the sintering method and combined methods. The main stages of thermochemistry-Bayer method are thermal activation of feedstock, its further desiliconization with the alkaline solution and leaching of the resultant bauxite product under Bayer’s method. Despite high energy consumption at the baking stage, it allows to condition the low quality bauxite feedstock by neutralizing a variety of technologically harmful impurities such as organic matter, sulfide sulfur, carbonates, and at the same time to remove crystalline hydrate and free water. Subsequent desiliconization of thermally activated bauxite with an alkaline solution allows to regrade it from low quality bauxites to feedstock suitable for processing by the Bayer method.
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