Obtaining Alumina from the Ash of Coal-Fired Power Plants

Russia's energy sector that uses coal for heat and electricity generation is a large source of ash and slags, the dumps of which occupy large areas and at the same time pose problems for the environment. These dumps contain, among other components, alumina and other valuable products. In the ash dumps from coal-fired power plants in the Ural region, approximately 350 million t of ash has been accumulated by now, and the amount continues to grow by 7-8 million t per annum. Given the conditions emerging on the world market, the obtaining of alumina from the ash and slag dumps at their own enterprises is a problem of Russia's metallurgical industry that is of utmost importance. Thus, the ashes from large, coal-fired thermal power plants in the Ural region of Russia, including the Troitsk, Reftinsk, Verkhnii Tagil, and other power plants, contain 28-32% of alumina and could become a man-made raw material for producing aluminum, thereby partially substituting the import of bauxites in Russia from foreign countries. The article presents the results of experimental studies aimed at elaborating a technology for extracting high-quality alumina from the alumina-rich ash of coal-fired power plants. The influence of various technological parameters on the target product's obtainment process is studied. At the first stage of this process, which involves partial desiliconization of ash by treating it with alkali solution, enriched alumina concentrate is extracted, which is close to low-grade bauxite raw material in its physicochemical properties. At the technology's second stage, a product with a 97-98% content of Al2O3 is obtained using the method of sintering the alumina concentrate with sodium and calcium carbonates; as a result, the alumina extraction ratio from ash is 88-90%.