Selenium leaching behaviors from MSWI fly ash and its control

A large number of fly ash samples from mechanical grate furnaces at a municipal solid waste incineration (MSWI) plant were examined including Se speciation and content. Se leaching behaviors before and after solidification/stabilization(S/S) treatment were comparatively studied. The results showed that Se in the MSWI fly ash was present mainly in the form of selenite with small amounts of physically adsorbed SeO 2 (s). Se in the low alkalinity ash (pH ∼ 7) tended to be more leachable than that in the high alkalinity ash (pH ∼ 12). The chelation treatment would further raise the risk of Se leaching into the environment from the low alkalinity ash (pH ∼ 7). Three Fe-containing additives (zero-valent iron (ZVI)、α-Fe 2 O 3 and Fe 3 O 4 ) were introduced, respectively in attempt to immobilize Se in the low alkalinity MSWI fly ash. A strong positive effect was found with ZVI addition in terms of Se leaching from low alkalinity chelated MSWI ash. Comparatively, iron oxides showed no obvious effect. The adjustment to ash alkalinity (CaO addition) exhibited a comparable effect to ZVI addition, which provided another option to control Se leaching from low alkalinity chelated ash.