Removal of arsenic in coal fly ash by acid washing process using dilute H 2SO 4 solvent

Abstract

Coal fly ash emitted from coal thermal power plants generally contains tens ppm of arsenic, one of the hazardous elements in coal, during combustion and their elution to soil or water has become a public concern. In this study, the acid washing process developed by the authors was applied to the removal of arsenic from coal fly ash. Laboratory- and bench-scale investigations on the dissolution behavior of arsenic from various coal fly ash samples into dilute H 2SO 4 were conducted. Arsenic in the coal fly ash samples were dissolved into H 2SO 4 solutions rapidly. However, its concentrations decreased with an increase in the pH of H 2SO 4 solution in some cases. The species of arsenic in the dilute H 2SO 4 was estimated as H 3AsO 4, and its anionic species was considered to adsorb with the elevation of pH under the presence of ash particle. Such adsorption behavior was enhanced under the presence of Fe ion in the solution. The sufficient removal of arsenic was achieved by controlling pH and avoiding the adsorption of arsenic on the surface of coal fly ash particles, and the elution of arsenic from coal fly ash sample was successfully below the regulation limit.