Speciation and Mobility Assessment of Zinc in Coastal Landfill Sites with MSW Incinerator Ash

Abstract

The mobility of zinc in coastal landfill sites reclaimed by municipal solid waste incinerator ash (MSWIA) was modeled and investigated by conducting a large column test. Temporal and spatial variations in the pH, redox potential (Eh), total organic carbon, and microbial activity were measured in pore water to observe their influences on the mobility of heavy metals throughout the test. After 502 days, permeation was terminated. Then to determine the content and forms of Zn along the column, MSWIA and marine clay samples were analyzed by the community bureau of reference modified sequential extraction procedure. Zn was partitioned into four defined chemical fractions: exchangeable, reducible, oxidizable, and residual. The results showed that attenuation processes occurred within the ash layer, Zn mobility was minor, and coastal landfill conditions promoted the immobilization of heavy metals. Both pH and Eh were the main factors for controlling the solubility of Zn. Moreover, under reduced-alkaline conditions, the reducible fraction was affected, but the oxidizable fraction was slightly favored. The formation of zinc sulphides might be another attenuation mechanism for Zn.