Journal
CHEMOSPHERE
Volume 300, Issue -, Pages -Publisher
PERGAMON-ELSEVIER SCIENCE LTD
DOI: 10.1016/j.chemosphere.2022.134571
Keywords
Fly ash; Heavy metal leaching characteristics; Leaching model; Long-term environmental risk
Categories
Funding
- National Key Research and Development Program of China [2018YFC1900103, 2021YFE0112100]
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This study investigated the leaching characteristics of different heavy metals in cement-solidified MSWIFA blocks and established mechanical models to estimate the long-term environmental risk. The results showed that the leaching of lead was controlled by diffusion, while the leaching of copper, chromium, arsenic, and nickel was mainly controlled by surface wash-off and diffusion.
Cement solidification is a commonly used pre-treatment method for municipal solid waste incineration fly ash (MSWIFA) prior to sanitary landfill. However, the long-term environmental risk of cement-solidified MSWIFA blocks in the exposed scenario of zoning sanitary landfill remains unclear. In this study, the leaching characteristics of different heavy metals in cement-solidified MSWIFA blocks under deionized water and acid rain scenarios were firstly investigated. The leaching control mechanisms of heavy metals were also explored and applied to established mechanical models for the estimation of long-term environmental risk. Results revealed that Pb leaching from cement-solidified MSWIFA blocks was controlled by diffusion; Cu, Cr and As leaching was mainly controlled by surface wash-off and diffusion; and Ni leaching was mainly controlled by diffusion and dissolution. Additionally, the established bulk diffusion, first-order reaction/diffusion and diffusion/dissolution models could accurately fit the abovementioned three types of heavy metals with different leaching control mechanisms (R-2 > 0.95). Under acid rain scenarios, according to the prediction results of the calibrated models, the cumulative leaching amount of Pb in 718 d was higher than the limit in GB16889-2008, the cumulative leaching amount of Cu, Cr, As and Ni did not exceed the limit in GB 16889-2008 even in 50 years. Therefore, the long-term environmental risk was relatively high for Pb but was low for Cu, Cr, As and Ni in cement-solidified MSWIFA blocks. This finding could be attributed to the strong alkali environment of cement-solidified MSWIFA blocks (pH > 12) that induced Pb salts (e.g. Pb(OH)(2) and PbSO4) dissolution. Therefore, the removal of partially soluble Pb salts from freshly made cement-solidified MSWIFA blocks by water or natural rainwater (e.g. without final cover system) washing in the initial landfilling stage (e.g. the leachate drainage system remains functional) is an effective countermeasure to reduce the environmental risks in zoning sanitary landfill.
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