Metal leaching from monolithic stabilised/solidified air pollution control residues

Area of Science:

• Environmental Science
• Materials Science
• Waste Management

Background:

• Air pollution control (APC) residues from municipal solid waste incineration pose environmental challenges.
• Effective stabilization/solidification (s/s) is crucial for safe disposal of these hazardous wastes.
• Existing waste acceptance criteria (WAC) guide the treatment process, but leaching mechanisms require further investigation.

Purpose of the Study:

• To evaluate the effectiveness of Portland cement (CEM I) and ground granulated blast furnace slag (ggbs) in treating APC residues.
• To determine optimal binder content for meeting UK monolithic Waste Acceptance Criteria (monWAC).
• To investigate the leaching mechanisms of contaminants from stabilized APC residues.

Main Methods:

• Preparation of stabilized/solidified (s/s) products using CEM I and ggbs at varying binder additions (10-50 wt.%) and water/solids ratios (0.40-0.80).
• Monolithic leach tests conducted according to EA NEN 7375:2004.
• Analysis of leaching data to assess compliance with monWAC and evaluate underlying mechanisms.

Main Results:

• 50% binder addition was required to meet monWAC for lead (Pb) and zinc (Zn).
• Chloride leaching exceeded WAC even at 50% binder addition.
• Lower binder additions (10% and 20%) were insufficient for lead reduction.
• Leaching processes were more complex than simple diffusion for s/s APC residues.

Conclusions:

• High binder content (50% CEM I + ggbs) is necessary for meeting Pb and Zn WAC in APC residue treatment.
• Chloride remains a concern, exceeding WAC even with high binder content.
• The study highlights the need to consider complex leaching mechanisms beyond diffusion for effective waste stabilization.