Portland cement (CEM I) and ground granulated blast furnace slag (ggbs) have been used to treat air pollution control (APC) residues from an energy-from-waste plant burning municipal solid waste. Stabilised/solidified (s/s) products were prepared with binder additions ranging from 10 to 50 wt.% of total dry mass and water/solids ratios between 0.40 and 0.80. Monolithic leach tests (EA NEN 7375:2004) indicated that 50% binder additions were necessary to meet the UK monolithic Waste Acceptance Criteria (monWAC) for Pb and Zn, and previous work indicated that chloride leaching exceeded WAC even at this binder addition. Lower binder additions (20 and 10%) did not sufficiently reduce leaching of Pb. Although the monWAC are based on an assumption that leaching is diffusion-controlled, evaluation of leaching mechanisms indicates that more complex processes than diffusion occur for s/s APC residues. (C) 2010 Elsevier B.V. All rights reserved.