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

the mineral phases of the diverse samples. Cu-Kα radiation The extent of carbonation was assessed by measuring the
(λ = 1.54060 Å) was employed in continuous scan mode, increase in CO loss from TGA after carbonation. To compare
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with a step size of 0.02° in the 2θ range spanning from mineralogical differences before and after carbonation,
15° to 90°. Heavy metal contents were determined by XRD analysis was conducted specifically for the IBA sample
digesting IBA samples (<0.6 mm and 0.6 – 1.12 mm only) carbonated with 10 wt% ammonium carbonate.
with a mixture of HNO and HBF followed by inductively Heavy metals such as Cd, Cr, Ni, and Pb in the filtrate
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coupled plasma-mass spectrometry. Digestion of IBA was were examined with an inductively coupled plasma-mass
performed according to a published method with slight spectrometer (ICP-MS; Perkin Elmer NexION 2000C,
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modifications. Small amount of IBA (<50 mg to make PerkinElmer, USA), while Cu and Zn were examined by
sure full digestion) with an accuracy of 1 mg was added means of inductively coupled plasma-optical emission
into a 15 mL Teflon vessel. Then, a pre-prepared HBF 4 spectroscopy (ICP-OES; Perkin Elmer Avio200, Perkin
solution (1.14 g boric acid dissolved in 3 mL of HF) was Elmer, USA). Sample preparation involved taking 20 mL of
added to the vessel followed by the slow addition of 7 mL the filtrate, passing it through a 0.45 µm PTFE membrane
of concentrated HNO acid (both HF and HNO are trace filter, acidifying with concentrated nitric acid to achieve a
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metal grade). HBF acid, instead of HF acid, was employed pH of 2 – 3, and finally adjusting the volume to 25 mL with
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due to the high content of Ca. HF alone will form insoluble deionized water.
CaF , which leads to incomplete digestion. The digestion
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was conducted in a microwave digestion machine (ETHOS 2.3. Leaching test and leachate characterisation
One, Milestone, Italy). The temperature was increased to A one-stage batch leaching test, conducted in accordance
230°C within 20 min and held at 230°C for 30 min. with UNE-EN-12457-2 standards, was employed to assess
Surface area measurements were obtained through the release of heavy metals in IBA. In this procedure, 9 g
N adsorption utilizing a Micromeritics ASAP2420MP of either native or carbonated IBA was mixed with 90 mL
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instrument (Micromeritics Instrument Corporation, of deionized water in a round-bottom flask, achieving a
USA). Thermogravimetric analysis (TGA) was performed liquid-to-solid ratio of 10. The flask was rotated on a rotary
using an SDT Q600 unit (TA Instruments, USA). In this evaporator for 24 h at atmospheric pressure, 30 rpm, and
process, 10 – 20 mg of ash underwent ramping at 10°C/min room temperature.
from 30°C to 900°C under a 100 cm /min flow of N . Following leaching, the resulting leachate underwent
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2.2. Accelerated carbonation filtration through a 0.45 µm PTFE membrane filter and
was subsequently acidified using concentrated nitric acid.
Carbonation investigations were exclusively conducted The concentrations of Cd, Cr, Cu, Ni, Pb, and Zn were
on IBA particles with a particle size below 0.6 mm. determined through ICP-MS. In addition, the pH value
Larger-sized IBA exhibits considerable heterogeneity in of each leachate was measured using a pH meter (OHAUS
composition and morphology, and the stirring process Starter3100) to provide comprehensive insights into the
has the potential to cause varying degrees of breakage, leaching behavior.
resulting in an even broader size range and complicating
the interpretation of results. 3. Results and discussion
Ammonium carbonate, from Sigma-Aldrich (ACS 3.1. Composition of native IBA
reagent), was employed as the carbonating agent. In each
experiment, 10 g of IBA was introduced to a 50 mL solution IBA is a heterogeneous material, both in terms of size and
of ammonium carbonate with varying concentrations. composition. Table 1 presents the XRF results for IBA with
Liquid/solid of 5 ensures a good mixing of the slurry. varying particle sizes and heavy metal contents determined
The mixture underwent stirring at room temperature for by ICP-MS. The table shows that the predominant oxides
1 h at 500 rpm. Subsequently, the residue was collected in IBA include Ca, Si, Fe, and Al, while Ca is the most
through filtration and dried overnight in an oven at 100°C. abundant element. Besides, the percentage of Ca decreases
Five distinct carbonated IBA samples were produced, with an increase in particle size, whereas Si and Fe exhibit
corresponding to ammonium carbonate concentrations an upward trend. This result agrees with the observation by
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of 2 wt%, 4 wt%, 6 wt%, 8 wt%, and 10 wt%, respectively. Um et al. and Beikmohammadi et al. who attributed it
,
These samples were designated as IBA-AC2, IBA-AC4, to the increased amount of glass and synthetic ceramics in
IBA-AC6, IBA-AC8, and IBA-AC10, with the numerical coarser fractions.
value representing the concentration of ammonium Calcium-containing alkaline minerals,
carbonate in percent by weight (denoting by “AC”). such as portlandite (Ca(OH) ), hydrocalumite
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Volume 1 Issue 1 (2024) 3 doi: 10.36922/eer.4609