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

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 H2SeO3. The dissolved H2SeO3 transformed into HSeO3- and adsorbed onto the surface of the ash particles in solution upon elevation of the pH. The re-elution of the absorbed HSeO3- as SeO32- at a pH of 10 was also confirmed, and will cause the elution of the excess selenium from the acid-washed ash.

► We have developed the acid washing process in order to remove boron, arsenic, and selenium in coal fly ash.
► The elution concentration of selenium in coal fly ash by the certified test method often beyond the regulation limit.
► An adsorption of HSeO3- on the surface of coal fly ash was observed at pH ≈ 4.
► The re-elution of HSeO3- as SeO32- at pH ≈ 10 was observed, which may cause an excess elution of selenium.