Leaching of arsenic from coal fly ashes 1. Leaching behavior of arsenic and mechanism study

The leaching of arsenic from coal fly ash NIST-1633b and NIST-2689 was tried with various lixiviants. The leaching of arsenic was found to have taken place readily and to be dependent on both the equilibria of dissolution/precipitation and adsorption/desorption in the leaching system. The arsenic leaching intensity was significantly elevated by the use of proper chelating agents, which is supposed to be owing to the formation of metal (aluminium and/or iron)-chelate complexes followed by an enhanced binding with arsenate ions. The results of the present study show that arsenic oxides are associated well with iron and aluminium oxide deposits on the particle surface of coal fly ash NIST-1633b. Surface enrichment for arsenic was also examined and confirmed by XPS measurement. The leaching percentages of arsenic on the surface from XPS detection were in good agreement with those in bulk found in the leaching tests.