Processing of Ash and Slag Waste from Coal-Fired Thermal Power Plants and Extraction of Commercial Products from the Waste (Review)

Abstract

Ash dumps of 170 large Russian coal-fired thermal power plants (TPPs) store more than 2 billion t of ash and slag waste (ASW) at present. They occupy approximately 50 000 ha and represent main sources of environmental pollution. The amount of ASW increases by approximately 20 million t every year. Besides the recorded amount of ASW, there is also waste that is not recorded in official documents. At the same time, the latter waste is man-made sources of commercial products. Direct large-scale application of ash is limited by the instability of its properties and its noncompliance with the applicable technical requirements for the products of its processing employed in various applications in power, metallurgical, chemical, construction, and other industries. Processing of ash and slag waste and gradual removal of ash dumps are a crucial state problem whose solution requires the development of appropriate industrial processes. The review examines modern methods of large-scale processing of ash and slag waste from coal-fired TPPs with extraction of commercial materials suitable for application in various industries. The emergence of a wide range of physical, chemical, and biological processes for ash processing enables the problem of reclamation of most ash dumps to be successfully solved. The attention was focused on such technologies as flotation enrichment, magnetic separation, and thermochemical methods. The mechanism of adsorption of functional groups of various collectors on the surface of carbon ash particles is examined. A large section of the review is devoted to acid, alkaline, and thermochemical methods of extracting alumina from ash and belite sludge. Attention is also focused on works dealing with the extraction of precious and rare earth metals from ash. Some new developing areas of microbiological extraction of metals from ash are also presented.