Evaluation of leaching characteristics of heavy metals from municipal solid waste incineration fly ash by up-flow percolation column tests
To determine the potential release of heavy metals from municipal solid waste incineration fly ash (MSWI-FA), the leaching behaviors of MSWI-FA from Likeng waste incineration power plant in China were characterized according to the US EPA method 1314. Heavy metals (i.e. Pb, Cr, Cd, Cu and Zn) leaching characteristics were investigated over a wide range of liquid-to-solid ratios (L/S 0.2–10 mL/g-dry) and different pH conditions (2, 4 and 6). The test results revealed that eluent with high pH of about 12 increased a little with increase of influent solutions pH. Similar concentration patterns of a heavy metal were observed at different pH influent solutions, and different concentration patterns for different heavy metals were showed at different liquid-to-solid ratio (L/S) range. Cumulative maximum release of heavy metals followed the pattern of Cr > Pb > Cu > Cd > Zn. The release of Pb and Cd decreased with pH of influent solutions while Cu and Zn changed oppositely. However, concentration of Cr did not significantly change and cumulative release linearly increased with L/S due to the leaching process was controlled by solubility. The effect of L/S ratio on Pb, Cd and Cu release in MSWI-FA indicated the prevalence of the dominant mechanism was either solubility or diffusion controlled. Zn extract concentrations were observed to decrease initially with L/S increase to 5 followed by a slight increase due to the presence of soluble zinc compounds in strong basic conditions.