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Explora: Environment
and Resource Accelerated carbonation for heavy metal inhibition in incineration bottom ash

Table 4. Leaching results of native and carbonated IBA (in µg/kg of metal/IBA) as well as NEA limit value for determining
application as construction materials
Heavy metal NEA limit value Native IBA IBA‑AC2 IBA‑AC4 IBA‑AC6 IBA‑AC8 IBA‑AC10
Cd 1 9.2 7.3 3.6 3.1 3.1 2.8
Cr 40 701.8 797.2 559.2 456.9 464.9 384.8
Cu 60 2519.6 630.0 385.8 353.5 317.7 275.3
Ni 10 338 128.9 87.4 80.2 88 91.6
Pb 20 2.4 0.9 1.2 1.0 0.7 2.1
Zn 200 83.1 45.3 38.5 43.1 34.4 32.3
Abbreviations: AC: Ammonium carbonate; IBA: Incineration bottom ash; NEA: The National Environment Agency of Singapore.

A B

Figure 3. Effect of AC concentration on solid and liquid phases. (A) IRs for different heavy metals versus concentration of (NH ) CO . (B) Concentration
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4 2
of heavy metals in the carbonating solution
Abbreviations: AC: Ammonium carbonate; IBA: Incineration bottom ash; IR: Inhibition rate.
of ash in construction materials, landfill disposal leaching
criteria may not be suitable, as leaching from construction
materials poses higher exposure risks for humans and
the surrounding. Indeed, as Table 4 shows, except Pb and
Zn, the content of all other heavy metals in the leachate
exceeds the limit set by the National Environment Agency,
although the accelerated carbonation improves their
leaching behavior effectively.
4. Conclusion
Figure 4. pH of the leachate for native IBA and carbonated IBA Leaching test results show the higher leaching rates for IBA
Abbreviations: AC: Ammonium carbonate; IBA: Incineration bottom ash.
with particle sizes below 2 mm for all heavy metals except
Pb and Zn. The low leaching rate of Pb and Zn is attributed
It has been suggested that the formation of neominerals to the effective natural weathering. The application of
during carbonation plays a role in immobilizing trace (NH ) CO as a carbonating agent proved effective,
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4 2
heavy metals. The reduction in pH after carbonation with concentration-dependent outcomes. Carbonation
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also aids in the formation of insoluble metal compounds, demonstrated notable efficiency in inhibiting heavy metal
especially those that are amphoteric. Table 4 presents leaching, particularly for Pb, Zn, and Cu. However, its
leaching values for IBA with a particle size below 0.6 mm. effectiveness varied across metals, with Cr exhibiting lower
Native IBA exhibits excessive leaching of Cu, while all IR. The study also highlighted the interconnected factors
carbonated IBAs have leaching values below the criteria influencing carbonation, such as pH reduction and the
set by the National Environment Agency of Singapore for formation of neominerals. Importantly, the results indicate
landfill disposal, classified as inert waste according to the that carbonation, while meeting landfill disposal criteria,
EU standard (EN 12457-2). However, for the utilization may necessitate re-evaluation when considering utilization

Volume 1 Issue 1 (2024) 7 doi: 10.36922/eer.4609