Assessment of long-term pH developments in leachate from waste incineration residues

Abstract

Environmental assessment of residue disposal needs to account for long-term changes in leaching conditions. Leaching of heavy metals from incineration residues are highly affected by the leachate pH; the overall environmental consequences of disposing of these residues are therefore greatly influenced by changes in pH over time. The paper presents an approach for assessing pH changes in leachate from municipal solid waste incineration (MSWI) air-pollution-control (APC) residues. Residue samples were subjected to a stepwise batch extraction method in order to obtain residue samples at a range of pH values (similar to common pH-dependence tests), and then on these samples to determine leaching of alkalinity as well as remaining solid phase alkalinity. On a range of APC residues covering various pretreatment and disposal options, this procedure was used to determine leachable and residual alkalinity as a function of pH. Mass balance calculations for typical disposal scenarios were used to provide data on pH as a function of the liquid-to-solid (L/S) ratio in the leaching system. Regardless of residue type and pretreatment, pH was found to stay above 7 for L/S ratios up to about 2000 L kg(-1) corresponding to about 100,000 years in typical landfill scenarios. It was found that pH changes were mainly governed by alkalinity decreases from leaching processes rather than neutralization reactions. The results suggest that leaching testing for assessment purposes should be carried out in the alkaline range, for example, at pH 9. The paper offers a thorough basis for further modelling of incineration residue leaching and for modelling the environmental consequences of landfilling and utilization of these residues.

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

“…Both values were fully comparable with those observed by Astrup et al [37] for similar types of residues. Alkalinity of leachates from the FA-columns was calculated using a mineral assemblage of gypsum, ettringite and calcite (no portlandite considered); calculated pH and alkalinity were found to 11.04 and 4.7 meq/L, i.e.…”

“…Similarly, the initial pH of the eluent (i.e. pH of distilled water before entering the columns) had only negligible effect (modeled, not shown) due to the huge acid-neutralization capacity of the residues [37].…”

Long-term mineral transformation of Ca-rich oil shale ash waste

“…These processes can affect its structural integrity, leading to deposit failure and/or potential leaching of hazardous components and contamination of the surroundings. Moreover, the waters draining off the deposits reach equilibrium with secondary Ca-phases and are highly alkaline (pH >12), posing environmental risks (Blinova et al, 2012) that need to be controlled in the short and long term (Astrup et al, 2006).…”

Acid neutralization capacity of waste - specification of requirement stated in landfill regulations

“…For alkaline waste materials (e.g. APC residues) containing soluble hydroxides in particular, the depletion in the long term will probably be more important than the neutralization potential of the minerals (Astrup et al 2006).…”