Ash from Coal-Fired Power Plants as a Raw Material for the Production of Alumina

Abstract

The energy sector of the Russian Federation based on coal to generate heat and electricity is a major source of ash and slag. The dumps of this waste occupy large areas and at the same time cause environmental problems. Ash and slag contain alumina and other valuable products such as silica, magnetite etc. The ashes of large thermal coal-fired power plants of the Ural region – Troitskaya, Reftinskaya, Verkhnetagilskaya and others – contain about 28-32 % wt alumina. The waste obtained could become the technogenic raw materials for the production of aluminum. This will allow partially replacing the import of alumina to Russia from foreign countries. The current work presents the results of experimental studies aimed at developing a technology for extracting high-quality alumina from the high-alumina ash of coal-fired power plants. In the study, the sintering method was used to obtain Al2O3 from ash for the first time. Because of high silica concentration in ash, the direct sintering cannot be applied. To remove SiO2, the ash samples collected from three thermal power plants of Ural region were preliminary treated with alkali solution and then thermally treated. The influence of various technological parameters on the process of obtaining the target product has been studied. To obtain an enriched alumina concentrate, the ash was found to be treated with 20 % wt of NaOH solution at 90-100 °C. The further thermal treatment should be performed at a temperature of 1,000-1,200 °C to activate ash. The sintering of the activated ash results in the production of Al2O3 with a purity of 97-98 % wt.