Long-term leaching from MSWI air-pollution-control residues: leaching characterization and modeling

Area of Science:

• Environmental Science
• Geochemistry
• Waste Management

Background:

• Municipal solid waste incineration (MSWI) produces air-pollution-control residues requiring safe disposal.
• Understanding the long-term leaching behavior of these residues is crucial for environmental risk assessment.

Purpose of the Study:

• To monitor the long-term leaching of various elements and dissolved organic carbon from MSWI residues.
• To identify solubility-controlling minerals and evaluate their interactions using geochemical modeling.
• To assess the environmental implications of MSWI residue disposal in landfills.

Main Methods:

• Column percolation experiments were conducted over 24 months, reaching high liquid-to-solid (L/S) ratios.
• Geochemical modeling using PHREEQC was employed to analyze mineral interactions and predict leaching behavior.
• Elemental concentrations in leachate were measured to quantify leaching.

Main Results:

• Less than 2% of As, Cu, Pb, Zn, Cr, and Sb leached, with many other elements showing minimal release (<1%).
• Geochemical modeling accurately predicted pH, alkalinity, and leaching of Ca, S, Al, Si, Ba, and Zn.
• Dissolution of ettringite-like phases was observed, correlating with Ca and S removal and leading to increased Sb and Cr leaching late in the experiments.

Conclusions:

• MSWI residues demonstrate low long-term leaching potential for many critical elements under simulated landfill conditions.
• Geochemical modeling is effective in predicting leaching behavior and identifying controlling mineral phases.
• The late-stage increase in oxyanion leaching highlights the importance of considering mineralogical transformations in long-term waste management strategies.