Beneficiation of coal ash from ash silos of six Chinese power plants and its risk assessment of hazardous elements for land application

Abstract

The tremendous amount of ash produced from coal-fired power plants must be disposed and utilized in an economically and environmentally sustainable manner. This paper conducted a study on the beneficiation of silo ashes and the risk assessment for land use. Silo ash samples were collected from six Chinese power plants and segregated into five size fractions by a combination of sieving and air classification. The concentration distributions of nine hazardous elements (i.e., As, Cd, Cr, Cu, Hg, Ni, Pb, Se, and Zn) were characterized. The results show that the particle size distributions of hazardous elements in the silo ashes do not exactly agree with the generally accepted models of their release and partitioning in the boiler. Environmental risks were assessed for agricultural and development land use of coal ash, according to related Chinese standards. The results suggest that all the bulk ashes meet the requirements for development land use. Beneficially, for some coal ashes, the coarse fraction (> 10 µm) can be applied to agricultural land while the remaining fraction (< 10 µm) still complies with the standard for development land use. This work demonstrates that a simple air classification is potentially an eco-friendly and value-added approach for the full utilization of coal ash.