Dissolution behavior of selenium from coal fly ash particles for the development of an acid-washing process

Abstract Coal fly ash emitted from coal-fired electric power stations generally contains environmentally regulated trace elements. In particular, boron, arsenic, and selenium have been recognized as troublesome trace elements because elutions from the fly ash contain them. In order to design an effective removal process for these trace elements, we have developed and investigated an acid-washing process. The dissolution behavior of selenium from coal fly ash particles was focused on for the improvement of the process, and was found to greatly depend on the pH of the acid solutions. The species of selenium in solutions with a pH of around 0–1 was determined to be H 2 SeO 3 . The dissolved H 2 SeO 3 transformed into HSeO 3 - and adsorbed onto the surface of the ash particles in solution upon elevation of the pH. The re-elution of the absorbed HSeO 3 - as SeO 3 2 - at a pH of 10 was also confirmed, and will cause the elution of the excess selenium from the acid-washed ash.