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Carbonation of municipal solid waste incineration electrostatic precipitator fly ashes in solution Aurore De Boom, Jean-Emmanuel Aubert and Marc Degrez Waste Manag Res 2014 32: 406 originally published online 9 April 2014 DOI: 10.1177/0734242X14527637 The online version of this article can be found at: http://wmr.sagepub.com/content/32/5/406
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WMR0010.1177/0734242X14527637Waste Management & ResearchDe Boom et al.
Original Article
Carbonation of municipal solid waste incineration electrostatic precipitator fly ashes in solution
Waste Management & Research 2014, Vol. 32(5) 406–413 © The Author(s) 2014 Reprints and permissions: sagepub.co.uk/journalsPermissions.nav DOI: 10.1177/0734242X14527637 wmr.sagepub.com
Aurore De Boom1, Jean-Emmanuel Aubert2 and Marc Degrez1
Abstract Carbonation was applied to a Pb- and Zn-contaminated fraction of municipal solid waste incineration electrofilter fly ashes in order to reduce heavy metal leaching. Carbonation tests were performed in solution, by Na2CO3 addition or CO2 bubbling, and were compared with washing (with water only). The injection of CO2 during the washing did not modify the mineralogy, but the addition of Na2CO3 induced the reaction with anhydrite, forming calcite. Microprobe analyses showed that Pb and Zn contamination was rather diffuse and that the various treatments had no effect on Pb and Zn speciation in the residues. The leaching tests indicated that carbonation using Na2CO3 was successful because it gave a residue that could be considered as non-hazardous material. With CO2 bubbling, Pb and Zn leaching was strongly decreased compared with material washed with water alone, but the amount of chromium extracted became higher than the non-hazardous waste limits for landfilling. Keywords Carbonation, fly ash, leaching, municipal solid waste incineration (MSWI)
Introduction Municipal solid waste incineration (MSWI) produces a variety of residues, namely bottom ash, fly ashes and air pollution control (APC) residues. Fly ashes correspond to the finest fraction of the remaining residues after thermal treatment; this fraction is transported by the flue gases beyond the furnace. When reactive substances are injected into the flue gases, fly ashes are mixed with the reaction products and the excess of the reactive substances; therefore, such a mix is not composed only by pure fly ashes and it constitutes the APC residues. If the APC system has an electrostatic precipitator (ESP) just after the boiler, without any reagent injection before the ESP, the ESP residues may also be considered as fly ashes, as it is the case in this article. Because of the different possible configurations of the APC system from one MSWI plant to another, distinguishing pure fly ashes from APC residues is not always obvious and their composition may largely differ. MSWI fly ashes and APC residues are considered as hazardous waste because they contain large quantities of chlorides, combined with significant concentrations of heavy metals, such as Cr, Pb and Zn, which may be leached by water. Consequently, the residues are usually treated by a stabilization/solidification process and are then landfilled. Recent studies have investigated new stabilization treatments including, among others, carbonation. Carbonation generally decreases inorganic contaminant mobility because of the pH change and the low solubility of carbonate compounds. Moreover, carbonation of alkaline residues captures atmospheric CO2 and
contributes to its storage (Baciocchi et al., 2006; Costa et al., 2007). APC residues could store as much as 120 g of CO2 kg-1 of dry solids (Baciocchi et al., 2006). Alkaline MSWI residue carbonation could be a CO2 capture and storage technique, especially for the CO2 coming from MSWI (Baciocchi et al., 2006; Prigiobbe et al., 2009). Carbonation occurs naturally through the presence of CO2 in the atmosphere and participates in solid weathering, especially of alkaline minerals (Costa et al., 2007). Natural carbonation is a rather slow process and carbonation must be accelerated if it is to be applied as a treatment for residues. Accelerated carbonation processes have largely been discussed by Costa et al. (2007). They have been developed according to two routes, indirect and direct, depending on whether the minerals to be carbonated are dissolved or not. In the indirect route, the first step is to extract the compounds and this is followed by carbonate precipitation. The direct method does not involve extraction; the gas is injected directly into a closed vessel containing either the solids or a solution of the solids. In such configurations, temperatures above 350
1Université 2Université
libre de Bruxelles (ULB), Brussels, Belgium de Toulouse, UPS, INSA, Toulouse, France
Corresponding author: Aurore De Boom, Université libre de Bruxelles (ULB); Brussels School of Engineering; 4MAT Department, Avenue F.D. Roosevelt 50, CP165/63, 1050 Brussels, Belgium. Email: [email protected]
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De Boom et al. Table 1. Initial and final pH after carbonation, leaching evolution after carbonation. Ash or residue description
Initial pH
Final pH
As Cl Cd Cr Cu Mo Ni Pb Sb Se SO42- Zn References
Aged fly ash Aged fly ash Aged fly ash Fly ash Fly ash Fly ash Fly ash
11.5–12 11.5–12 11.5–12 12–12.5 12–12.5 12–12.5 12.1
MSWI fly ash Revasol treated fly ash Medical SWI APC ash - 200°C Medical SWI APC ash - 300°C Medical SWI APC ash - 400°C Medical SWI APC ash MSWI fly ash MSWI APC residues MSWI APC residues MSWI APC residues MSWI APC residues
12.51 6.6 12.4
7.5–8 10–10.5 10–10.5 7 11.5–12 6–6.5 12 (10 h) to – 7–8 (300 h) 12.14 10.3 – 12.4
12.4
– – – – ~ ~
+ ~ ~ + + + +
Li et al., 2007 Li et al., 2007 Li et al., 2007 Li et al., 2007 Li et al., 2007 Li et al., 2007 Wang et al., 2010
~ –
+ – +
Todorovic and Ecke, 2006 Aubert et al., 2006 Baciocchi et al., 2009
+
12
–
+
–
–
Baciocchi et al., 2009
12.4
12
+
–
–
–
Baciocchi et al., 2009
12.4 12–12.5 12.45 12.5–13 13 11.8–12
11.6 11 9.77 12.5 10.5–10.7 10.8
–
–
–
–
–
+ – – –
–
–
– + – –
bl2 bl2 – ~ ~ – – – – – –
~ – – –
Baciocchi et al., 2009 Jianguo et al., 2009 Todorovic and Ecke, 2006 Quina et al., 2011 Cappai et al., 2012 Sicong et al., 2011
– ~ ~
–
~ + +
– – – ~ ~ + –
~ – +
–
~ –
– ~ ~ ~ – +
~ + +
–
– –1 –
– – – – – – –
+ +
– +
+ +
–
+ –
1soluble
fraction, 2 bl : below detection limit. –: leaching decreased; +: leaching increased; ~: leaching remained stable.
°C seem to be necessary to achieve carbonation (Prigiobbe et al., 2009). The direct route may be exploited at an MSWI plant, by using the flue gases as a source of CO2 (Ecke et al., 2000). The carbonation may be influenced by several factors, principally the liquid-to-solid (L/S) ratio, the temperature, the partial pressure of CO2, the reaction time, the particle size and the chemical composition of the residues (Baciocchi et al., 2006; Costa et al., 2007; Ecke, 2003; Fernández Bertos et al., 2004; Li et al., 2007). Baciocchi et al. (2006) obtained a maximum CaCO3 formation at 400 °C by applying a direct gas–solid carbonation on APC residues from a medical solid waste incinerator. Li et al. (2007) found an optimal L/S ratio of 0.3, based on the ash weight gain. The optimal L/S ratio results from a compromise between the reaction promoted by the water and the pores blocked by too much water (Fernández Bertos et al., 2004; Li et al., 2007). Li et al. (2007) also studied the influence of temperature on carbonation: a temperature of 21 °C gave the highest CaCO3 formation after 30 minutes. Using indirect carbonation, Chiang et al. (2001) achieved the highest extracted amounts of Cd and Cr by using an L/S ratio of 40 at pH 3. Carbonation influences the leaching of some compounds from the treated ashes and residues, but the influence is not systematic, as Table 1 reveals. Carbonation may increase, decrease or not affect the leaching of Cd, Cr, Cu, Mo and sulphates. Pb and Zn leaching generally decreases after carbonation but some exceptions occur (Costa et al., 2007). Carbonation seems to increase Sb leaching, which has been also noticed and studied in the case of bottom ash at pH>12 (Cornelis et al., 2006). Chloride leaching
decreased after carbonation, owing to the salt dissolution during the carbonation in solution acting as a washing step. However, these data show how delicate it is to conclude on a general effect of carbonation on heavy metal leaching. The carbonation effect on the leachability of residues may be related to the pH obtained and the solubility of compounds at that pH, while the formation of new compounds could also be responsible. Shimaoka et al. (2002) suggested that Pb substitutes Ca in compounds like gypsum (CaSO4.2H2O) and vaterite (CaCO3). This article reports the application of carbonation to a fraction contaminated with heavy metals (Pb and Zn), obtained from ESP fly ashes by sieving at 38 µm (De Boom & Degrez, 2009). The carbonation aims to reduce the leachability of heavy metals. The carbonation treatment consisted of mixing the ashes with Na2CO3 and of injecting CO2 into a solution. The use of carbonation, which in itself has not been optimized as the main goal, was to observe its effects on ESP fly ashes, to know if such a treatment is worthy to be used. The chemical and mineralogical characteristics of the resulting residues were studied and special attention was paid to the leachability of harmful elements, measured according to the standard European leaching test (EN 12457-2, 2002).
Materials and methods Materials ESP fly ashes (200 L) were sampled at a Belgian MSWI plant (De Boom & Degrez, 2012). No reagent is injected before the ESP so the residues were considered as ‘pure’ fly ashes.
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The ashes were first mixed with a brine solution (L/S ratio of 5 L kg-1) for 2 h and sieved at 38 µm. The brine solution (pH 11.5) came from previous ash washings. The fraction below 38 µm was recovered and washed with water to remove the main soluble salts (NaCl, KCl). The residues were then carbonated in solution, by adding Na2CO3 or by injecting pure CO2 by means of a sintered glass vessel. Na2CO3 concentration was equivalent to twice the Ca molar concentration. The mixing with Na2CO3 in solution lasted 2 h, while the injection of CO2 took 20 min at a flow of 0.5 L min-1. The effects of carbonation were compared with simple washing by water. The different treatments were labelled H2OH2O, H2O-Na2CO3 and H2O-CO2.
Analysis methods The solid composition was determined by X-ray fluorescence (XRF) (Siemens RS 3000, Be source, Rh-anti-cathode, OVO 55 analyser crystal). Thermo gravimetric analyses (TGA) were carried out on samples of ashes to measure their CO2 content. The samples were heated to 850 °C at a constant rate of 10 °C min-1. The crystalline phases were identified using a Siemens D5000 powder X-ray diffractometer equipped with a monochromator using a cobalt anticathode (λ = 1.789 Å). Quantitative analyses were performed using a CAMECA SX50 microprobe with SAMx automation. The operating conditions were: accelerating voltage 15 kV, beam current 10 nA and analysed surface approximately 3 µm × 3 μm. Natural and synthetic minerals were used as standards. Detection limits for Zn and Pb are 0.3 and 0.4%, respectively. Leaching tests were applied to residues mixed with deionized water (L/S = 10 L kg-1) for 24 hours in a rotary agitation device (EN 12457-2, 2002). Solutions were then filtrated on 0.45 µm-membranes (Millipore). Cr, Cu, Pb and Zn concentrations were analysed by Inductively Coupled Plasma Optical Emission Spectroscopy (ICP-OES, Varian VISTA-MPX CCD Simultaneous). Chlorides were qualitatively estimated by chloride titrators (Hach).
Results and discussion Chemical composition Raw ESP fly ashes and treatment residues contain Ca as a major cationic component (expressed as CaO), as shown in Table 2. The concentration of CaO increases after the treatment, mainly because of the dissolution of soluble salts (NaCl, KCl expressed as Cl, Na2O and K2O in Table 2), but also because of the formation of calcite, especially in the H2O-Na2CO3 treatment. The fluctuations in S (as SO3) concentration are also noteworthy; in case of the H2O-Na2CO3 treatment, the SO3 concentration dropped to 2.9%, reflecting the reaction of anhydrite with Na2CO3 according to: Na2CO3 + CaSO4 → Na2SO4 + CaCO3. This reaction produced soluble sodium sulphate, which then dissolved in the washing water, and calcite (CaCO3). The carbonation effect of H2O-Na2CO3 and H2O-CO2 treatments was highlighted by the
Table 2. Chemical composition of raw ESP and treated residues, in oxides (%). %
Raw
H2O-H2O
H2O-Na2CO3
H2O-CO2
CaO Cl SO3 Na2O K2O SiO2 Al2O3 CO2 ZnO P2O5 TiO2 MgO Fe2O3 PbO SnO2 Br CuO Sb2O3 BaO Cr2O3 MnO
22.2 20.0 14.1 13.5 8.4 7.6 3.7 2.2 2.0 1.9 1.3 1.1 0.89 0.42 0.14 0.13 0.10 0.10 0.08 0.08 0.04
36.3 0.4 22.3 0.3 1.1 12.0 6.2 4.0 5.9 4.0 1.9 1.5 0.8 0.81 0.28 n.d. 0.18 0.19 0.17 0.44 1.1
44.5 0.7 2.9 2.4 0.8 14.5 5.7 7.9 6.9 4.5 2.4 2.7 1.8 0.87 0.33 n.d. 0.24 0.22 0.20 0.23 0.09
34.2 0.7 16.5 0.6 0.9 13.8 7.3 6.0 7.0 4.5 2.1 2.6 1.5 0.99 0.25 n.d. 0.33 0.15 0.20 0.21 0.08
n.d.: non detected.
increase in the CO2 content of the ashes. Heavy metals, especially Zn, appeared to be generally more concentrated in the treated residues, because these residues correspond to the solid fraction below 38 µm richer in heavy metal compounds (De Boom & Degrez, 2009), as these compounds preferably condense on small particles (Chandler et al., 1997).
Mineralogy Thirteen mineralogical compounds in raw ESP fly ashes were identified by X-ray diffraction (XRD) (Figure 1). Among those compounds, chlorides (halite and sylvite) were the most abundant. After treatment, the chloride salts were removed from the solids because of their high solubility (see Figure2). Residues from H2O-H2O and H2O-CO2 treatment mainly consisted of anhydrite and calcite, while H2O-Na2CO3 residues only contained calcite. The absence of anhydrite in H2O-Na2CO3 residues may be owing to the transformation of anhydrite into calcium carbonate, which is a thermodynamically more stable component (Fernández-Díaz et al., 2010). The precise calcium carbonate mineral formed (calcite or vaterite, CaCO3) depends on the ratio between CO32- and SO42- anions: if SO42-/CO32- > 1, vaterite forms while, if the ratio is < 1, calcite precipitates, as was the case in the present work (Fernández-Díaz et al., 2010). Some microprobe analyses were conducted on the treatment residues to complete the mineralogical characterization performed by XRD. Table 3 summarizes the different compounds identified by XRD and microprobe. Over 100 spots were analysed by microprobe for H2O-H2O and H2O-CO2 residues, while only 50 were
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De Boom et al.
Figure 1. Raw ESP fly ashes – XRD diffractograms.
Figure 2. Treatment residues – XRD diffractograms.
taken for H2O-Na2CO3 residues because of the massive presence of aggregates in which individual particles were not easy to distinguish from the resin. As the technique does not identify H or C, hydrated and carbonated compounds were expected to present a deficit in their analysis (total largely below 100%). Microprobe
analyses confirmed the presence of perovskite and hematite, which was only supposed from XRD study owing to the significant overlapping of diffraction peaks. Moreover, microprobe analyses also indicated the scarcity of quartz in all the treatment residues. As the residues have been sieved at 38 µm, their small size may explain
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Table 3. Mineral compounds present in the different residues – XRD and microprobe analyses. Raw H2O- H2OH2OH2O Na2CO3 CO2 Quartz Anhydrite Bassanite Gehlenite Portlandite Calcite Perovskite Halite Sylvite Hydrocalumite Hematite Hydroxylapatite
SiO2 CaSO4 CaSO4.0.5H2O Ca2Al2SiO7 Ca(OH)2 CaCO3 CaTiO3 NaCl KCl Ca4Al3O6Cl2.10H2O Fe2O3 Ca5(PO4)3OH
X X X X X X X X X X X X
X X X X
X
X X
X X
X X
X X
X
X X X X X X X X
the scarcity of quartz (Bodénan et al., 2010; Thipse et al., 2002). Finally, a few minerals rich in K were measured in the raw sample and could correspond to feldspars, such as microcline, which it was not possible to identify using XRD analyses because of the number of minerals contained by the ash and the low concentration of this phase.
Pb and Zn speciation The microprobe analyses also identified some particles or aggregates presenting higher levels of heavy metals, especially Zn and Pb. The 250 analyses conducted on the three treated ashes seemed to show that Zn contamination was rather diffuse in the different residues. However, a few particles containing more than 5% ZnO were detected (see Table 4). Particles presenting such high concentrations in heavy metal compounds may determine the hazardous character of the residue. The particle matrix generally consisted of CaO, while some analyses revealed high levels of SiO2 or SO3 in some particles. In H2O-H2O residues, high concentrations of ZnO may also have been associated with the presence of MgO (one particle containing 36% of other compounds, mainly MgO in this case). In H2O-Na2CO3 residues, ZnO seemed to be linked with higher concentration of Fe2O3 or SiO2. The H2O-CO2 residues presented the highest ZnO levels, associated with relatively high concentrations of SiO2 and Al2O3. Some TiO2 rich particles were also visible. As for Zn, some Pb-rich particles were also identified (see Table 5). The particles systematically presented CaO, SO3 and ZnO. In H2O-Na2CO3 and H2O-CO2 residues, TiO2-rich particles were also detected. These results showed that the ash contamination in Pb and Zn was diffuse, whatever the ash treatment. So, the treatments did not influence the Pb and Zn speciation.
Leaching behaviour The leaching tests showed that all the treatments efficiently removed the chlorides (see Table 6). The washing with water only
led to the extraction of amounts above the non-hazardous waste limits for landfilling in the case of Pb (2003/33/EC). The carbonation using Na2CO3 reduced the leaching of Pb and thus allowed the residue to be considered as a non-hazardous material, even though Cr and Zn leaching increased slightly with this treatment compared with washing using water only. In the same way, bubbling with gaseous CO2 considerably improved the Pb and Zn leaching, their extracted amounts becoming undetectable. With such treatment, the chromium leaching increase prevented the residue from being considered as a non-hazardous material. The results presented in this article are comparable with those found in the literature (Table 1): carbonation leads to a decrease in Pb and Zn leaching that may be directly related to the pH falling to just below 11, where Pb and Zn compounds can precipitate (Van Herck et al., 2000). The carbonation increased the leaching amount of Cr. According to Baciocchi et al. (2007), the increase could be related to the fact that the pH decreased in the case of H2O-CO2, where the Cr leaching increase was more marked. However, it is rather difficult to explain the Cr leaching behaviour. Astrup et al. (2005) studied Cr leaching from APC residues, considering that Cr is mainly present as Cr(VI). At the contrary, Cr(III) has been principally found in MSWI fly ash by Hu et al. (2013), which is reinforced by the low leaching of Cr from fly ash, compared with bottom ash, related by Verbinnen et al. (2013) and by the small proportion of leached Cr compared with the total context (8.95%) indicated by Chiang et al. (2009). By assuming that Cr is mainly present as Cr(III) in the initial residues, a leaching increase may be due to oxidation of Cr(III) to Cr(VI) being more soluble. Verbinnen et al. (2013) proved by thermodynamics and kinetics that the oxidation of Cr(III) by O2 in the presence of alkali is favoured, which could have thus happened during the carbonation experiments of the present study.
Conclusion The effect of carbonation on the mineralogy of MSWI electrofilter (ESP) fly ashes and on the leaching of heavy metals was investigated in this work. Carbonation was achieved either by Na2CO3 mixing or by CO2 bubbling in water. All the carbonation treatments led to the dissolution of chlorides (NaCl, KCl), the formation of carbonate compounds (mainly calcite) and, in the case of Na2CO3 mixing, anhydrite removal. Pb and Zn speciation was studied using microprobe analysis to identify possible effects of the carbonation treatments on the stabilization of the elements in some specific phases. Microprobe analyses of the residues obtained with the three treatments under study (washing with water only, Na2CO3 addition and CO2 bubbling) were comparable and Pb and Zn contamination appeared to be rather diffuse. Thus, microprobe analyses did not highlight all the effects of the various treatments on the speciation of Pb and Zn in the residues. In spite of this, the results of the leaching tests carried out on the three residues showed significant differences. The carbonation using Na2CO3 decreased the leaching of Pb compared with the washing with only water and thus permitted
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De Boom et al. Table 4. Oxide compounds (%) detected in particles containing more than 5% in ZnO – microprobe analyses (‘Other’ corresponds to the sum of K2O, MgO, Na2O and P2O5). %
Total
CaO
SiO2
Al2O3
SO3
TiO2
Fe2O3
ZnO
PbO
Other
H2O-H2O H2ONa2CO3 H2O-CO2
98.0 59.4 76.3 38.0 28.8 34.1 33.0 36.0 39.7 23.4 69.5 72.8 89.4 95.8 83.6 101.1 34.4 90.3 50.4 46.8 40.6 32.9 40.1 36.6 32.6
35.2 8.1 15.1 12.8 9.4 7.0 12.0 12.4 16.2 7.1 41.5 6.3 7.0 22.7 28.2 16.5 12.3 25.7 9.3 18.9 12.0 9.4 12.5 13.9 10.3
45.9 28.7 0.7 5.6 2.5 6.8 3.2 3.8 5.3 2.7 6.5 7.9 5.5 31.5 39.1 37.2 5.9 22.2 11.5 9.9 9.7 5.1 5.6 5.9 5.8
6.3 4.3 0.3 2.1 1.1 5.3 1.7 2.4 2.0 1.4 0.2 3.7 2.3 23.4 2.8 9.5 2.1 14.4 7.0 7.1 5.1 2.6 2.4 3.2 3.3
0.3 4.4 16.6 5.5 5.1 4.9 4.7 4.3 3.8 2.6 2.2 0.1 0.1 0.1 0.1 0.0 3.1 0.8 3.1 1.2 4.3 4.8 3.3 2.1 3.5
0.2 1.5 0.1 0.0 0.0 0.5 1.3 0.1 0.4 0.0 6.2 0.2 0.4 0.4 0.4 6.1 1.9 0.2 0.6 0.9 0.3 0.5 0.1 0.1 0.2
0.4 0.3 0.5 0.7 0.2 0.2 1.1 0.3 0.4 0.2 0.1 34.5 63.7 1.0 1.8 0.9 0.7 0.5 0.8 0.2 0.6 0.3 0.5 0.5 0.8
5.0 7.8 6.8 8.5 7.3 8.2 5.2 9.9 6.4 5.1 7.4 17.5 5.9 8.2 5.7 7.4 5.5 22.5 13.1 5.4 5.4 7.0 6.7 6.1 5.9
0.3 0.3 0.2 0.7 0.5 0.2 0.6 0.7 0.6 0.2 3.9 0.1 0.1 0.2 0.4 0.1 0.6 0.4 1.1 1.1 0.5 1.1 0.5 1.1 0.8
4.2 4.1 36.0 2.2 2.7 1.1 3.2 2.1 4.5 4.2 1.4 2.5 4.4 8.3 5.0 23.5 2.3 3.6 3.8 2.1 2.7 2.0 8.6 3.8 2.0
Data in bold indicate higher concentrations.
Table 5. Oxide compounds (%) detected in particles with more than 0.8% in PbO – microprobe analyses.
H2O-H2O H2ONa2CO3 H2O-CO2
Total
CaO
SiO2
Al2O3
SO3
TiO2
Fe2O3
ZnO
PbO
Other
70.2 54.5 46.2 86.7 52.6 56.3 53.0 42.2 37.1 26.8 63.6 40.5 20.6 82.6 41.0 50.5 41.3 54.4 35.9 26.9 21.7 25.4
29.8 19.9 20.9 52.1 22.4 48.9 46.5 18.1 16.5 11.7 33.0 23.5 6.0 39.6 17.1 28.1 18.2 28.9 11.8 15.4 5.8 4.5
2.1 4.2 2.9 20.3 11.3 1.2 0.9 3.4 3.2 3.5 7.2 5.9 5.8 15.4 2.8 5.4 3.7 7.7 7.1 2.4 5.3 6.3
1.2 2.7 5.7 0.5 3.6 0.2 0.1 4.3 1.1 1.5 2.3 1.3 1.3 2.2 2.6 5.1 1.7 5.7 3.4 1.2 2.6 3.6
27.6 19.8 11.8 8.9 6.5 1.9 1.8 8.5 5.2 3.7 4.2 1.3 0.6 11.9 9.9 8.9 2.6 5.2 4.0 3.3 1.1 1.0
1.3 0.3 2.3 1.1 0.1 0.1 0.1 3.2 0.0 0.1 11.4 0.8 0.1 0.5 0.0 0.0 9.5 1.1 0.7 0.0 0.2 0.2
0.4 0.3 0.1 0.1 0.4 0.1 0.3 0.7 0.4 0.4 0.8 2.8 0.6 3.5 0.2 0.2 0.5 0.5 0.6 0.3 0.4 0.6
1.3 3.8 1.2 1.9 3.2 2.1 1.5 1.9 4.8 3.3 2.0 2.2 2.4 2.1 4.6 1.0 2.8 2.3 4.4 2.3 3.9 4.7
0.8 0.9 0.9 0.9 3.0 1.1 1.2 0.8 1.0 0.8 0.8 0.9 0.8 1.2 1.4 1.2 0.9 1.4 0.9 0.8 0.9 1.0
5.7 2.7 0.4 1.0 2.0 0.7 0.6 1.2 4.7 2.0 1.8 2.0 3.0 6.2 2.3 0.6 1.5 1.7 3.1 1.2 1.6 3.6
Data in bold indicate higher concentrations.
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Table 6. Amounts of Cl (g kg-1), Cr, Cu, Pb and Zn (mg kg-1) extracted and pH after the leaching test, compared with European limits for landfilling (2003/33/EC). Cl
Cr
Cu
g kg-1 mg kg-1
H2O-H2O H2O-Na2CO3 H2O-CO2 Hazardous waste limit Non-hazardous waste limit
0.3 0.2 0.2 25 15
Carbonation of municipal solid waste incineration electrostatic precipitator fly ashes in solution Aurore De Boom, Jean-Emmanuel Aubert and Marc Degrez Waste Manag Res 2014 32: 406 originally published online 9 April 2014 DOI: 10.1177/0734242X14527637 The online version of this article can be found at: http://wmr.sagepub.com/content/32/5/406
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On behalf of:
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research-article2014
WMR0010.1177/0734242X14527637Waste Management & ResearchDe Boom et al.
Original Article
Carbonation of municipal solid waste incineration electrostatic precipitator fly ashes in solution
Waste Management & Research 2014, Vol. 32(5) 406–413 © The Author(s) 2014 Reprints and permissions: sagepub.co.uk/journalsPermissions.nav DOI: 10.1177/0734242X14527637 wmr.sagepub.com
Aurore De Boom1, Jean-Emmanuel Aubert2 and Marc Degrez1
Abstract Carbonation was applied to a Pb- and Zn-contaminated fraction of municipal solid waste incineration electrofilter fly ashes in order to reduce heavy metal leaching. Carbonation tests were performed in solution, by Na2CO3 addition or CO2 bubbling, and were compared with washing (with water only). The injection of CO2 during the washing did not modify the mineralogy, but the addition of Na2CO3 induced the reaction with anhydrite, forming calcite. Microprobe analyses showed that Pb and Zn contamination was rather diffuse and that the various treatments had no effect on Pb and Zn speciation in the residues. The leaching tests indicated that carbonation using Na2CO3 was successful because it gave a residue that could be considered as non-hazardous material. With CO2 bubbling, Pb and Zn leaching was strongly decreased compared with material washed with water alone, but the amount of chromium extracted became higher than the non-hazardous waste limits for landfilling. Keywords Carbonation, fly ash, leaching, municipal solid waste incineration (MSWI)
Introduction Municipal solid waste incineration (MSWI) produces a variety of residues, namely bottom ash, fly ashes and air pollution control (APC) residues. Fly ashes correspond to the finest fraction of the remaining residues after thermal treatment; this fraction is transported by the flue gases beyond the furnace. When reactive substances are injected into the flue gases, fly ashes are mixed with the reaction products and the excess of the reactive substances; therefore, such a mix is not composed only by pure fly ashes and it constitutes the APC residues. If the APC system has an electrostatic precipitator (ESP) just after the boiler, without any reagent injection before the ESP, the ESP residues may also be considered as fly ashes, as it is the case in this article. Because of the different possible configurations of the APC system from one MSWI plant to another, distinguishing pure fly ashes from APC residues is not always obvious and their composition may largely differ. MSWI fly ashes and APC residues are considered as hazardous waste because they contain large quantities of chlorides, combined with significant concentrations of heavy metals, such as Cr, Pb and Zn, which may be leached by water. Consequently, the residues are usually treated by a stabilization/solidification process and are then landfilled. Recent studies have investigated new stabilization treatments including, among others, carbonation. Carbonation generally decreases inorganic contaminant mobility because of the pH change and the low solubility of carbonate compounds. Moreover, carbonation of alkaline residues captures atmospheric CO2 and
contributes to its storage (Baciocchi et al., 2006; Costa et al., 2007). APC residues could store as much as 120 g of CO2 kg-1 of dry solids (Baciocchi et al., 2006). Alkaline MSWI residue carbonation could be a CO2 capture and storage technique, especially for the CO2 coming from MSWI (Baciocchi et al., 2006; Prigiobbe et al., 2009). Carbonation occurs naturally through the presence of CO2 in the atmosphere and participates in solid weathering, especially of alkaline minerals (Costa et al., 2007). Natural carbonation is a rather slow process and carbonation must be accelerated if it is to be applied as a treatment for residues. Accelerated carbonation processes have largely been discussed by Costa et al. (2007). They have been developed according to two routes, indirect and direct, depending on whether the minerals to be carbonated are dissolved or not. In the indirect route, the first step is to extract the compounds and this is followed by carbonate precipitation. The direct method does not involve extraction; the gas is injected directly into a closed vessel containing either the solids or a solution of the solids. In such configurations, temperatures above 350
1Université 2Université
libre de Bruxelles (ULB), Brussels, Belgium de Toulouse, UPS, INSA, Toulouse, France
Corresponding author: Aurore De Boom, Université libre de Bruxelles (ULB); Brussels School of Engineering; 4MAT Department, Avenue F.D. Roosevelt 50, CP165/63, 1050 Brussels, Belgium. Email: [email protected]
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De Boom et al. Table 1. Initial and final pH after carbonation, leaching evolution after carbonation. Ash or residue description
Initial pH
Final pH
As Cl Cd Cr Cu Mo Ni Pb Sb Se SO42- Zn References
Aged fly ash Aged fly ash Aged fly ash Fly ash Fly ash Fly ash Fly ash
11.5–12 11.5–12 11.5–12 12–12.5 12–12.5 12–12.5 12.1
MSWI fly ash Revasol treated fly ash Medical SWI APC ash - 200°C Medical SWI APC ash - 300°C Medical SWI APC ash - 400°C Medical SWI APC ash MSWI fly ash MSWI APC residues MSWI APC residues MSWI APC residues MSWI APC residues
12.51 6.6 12.4
7.5–8 10–10.5 10–10.5 7 11.5–12 6–6.5 12 (10 h) to – 7–8 (300 h) 12.14 10.3 – 12.4
12.4
– – – – ~ ~
+ ~ ~ + + + +
Li et al., 2007 Li et al., 2007 Li et al., 2007 Li et al., 2007 Li et al., 2007 Li et al., 2007 Wang et al., 2010
~ –
+ – +
Todorovic and Ecke, 2006 Aubert et al., 2006 Baciocchi et al., 2009
+
12
–
+
–
–
Baciocchi et al., 2009
12.4
12
+
–
–
–
Baciocchi et al., 2009
12.4 12–12.5 12.45 12.5–13 13 11.8–12
11.6 11 9.77 12.5 10.5–10.7 10.8
–
–
–
–
–
+ – – –
–
–
– + – –
bl2 bl2 – ~ ~ – – – – – –
~ – – –
Baciocchi et al., 2009 Jianguo et al., 2009 Todorovic and Ecke, 2006 Quina et al., 2011 Cappai et al., 2012 Sicong et al., 2011
– ~ ~
–
~ + +
– – – ~ ~ + –
~ – +
–
~ –
– ~ ~ ~ – +
~ + +
–
– –1 –
– – – – – – –
+ +
– +
+ +
–
+ –
1soluble
fraction, 2 bl : below detection limit. –: leaching decreased; +: leaching increased; ~: leaching remained stable.
°C seem to be necessary to achieve carbonation (Prigiobbe et al., 2009). The direct route may be exploited at an MSWI plant, by using the flue gases as a source of CO2 (Ecke et al., 2000). The carbonation may be influenced by several factors, principally the liquid-to-solid (L/S) ratio, the temperature, the partial pressure of CO2, the reaction time, the particle size and the chemical composition of the residues (Baciocchi et al., 2006; Costa et al., 2007; Ecke, 2003; Fernández Bertos et al., 2004; Li et al., 2007). Baciocchi et al. (2006) obtained a maximum CaCO3 formation at 400 °C by applying a direct gas–solid carbonation on APC residues from a medical solid waste incinerator. Li et al. (2007) found an optimal L/S ratio of 0.3, based on the ash weight gain. The optimal L/S ratio results from a compromise between the reaction promoted by the water and the pores blocked by too much water (Fernández Bertos et al., 2004; Li et al., 2007). Li et al. (2007) also studied the influence of temperature on carbonation: a temperature of 21 °C gave the highest CaCO3 formation after 30 minutes. Using indirect carbonation, Chiang et al. (2001) achieved the highest extracted amounts of Cd and Cr by using an L/S ratio of 40 at pH 3. Carbonation influences the leaching of some compounds from the treated ashes and residues, but the influence is not systematic, as Table 1 reveals. Carbonation may increase, decrease or not affect the leaching of Cd, Cr, Cu, Mo and sulphates. Pb and Zn leaching generally decreases after carbonation but some exceptions occur (Costa et al., 2007). Carbonation seems to increase Sb leaching, which has been also noticed and studied in the case of bottom ash at pH>12 (Cornelis et al., 2006). Chloride leaching
decreased after carbonation, owing to the salt dissolution during the carbonation in solution acting as a washing step. However, these data show how delicate it is to conclude on a general effect of carbonation on heavy metal leaching. The carbonation effect on the leachability of residues may be related to the pH obtained and the solubility of compounds at that pH, while the formation of new compounds could also be responsible. Shimaoka et al. (2002) suggested that Pb substitutes Ca in compounds like gypsum (CaSO4.2H2O) and vaterite (CaCO3). This article reports the application of carbonation to a fraction contaminated with heavy metals (Pb and Zn), obtained from ESP fly ashes by sieving at 38 µm (De Boom & Degrez, 2009). The carbonation aims to reduce the leachability of heavy metals. The carbonation treatment consisted of mixing the ashes with Na2CO3 and of injecting CO2 into a solution. The use of carbonation, which in itself has not been optimized as the main goal, was to observe its effects on ESP fly ashes, to know if such a treatment is worthy to be used. The chemical and mineralogical characteristics of the resulting residues were studied and special attention was paid to the leachability of harmful elements, measured according to the standard European leaching test (EN 12457-2, 2002).
Materials and methods Materials ESP fly ashes (200 L) were sampled at a Belgian MSWI plant (De Boom & Degrez, 2012). No reagent is injected before the ESP so the residues were considered as ‘pure’ fly ashes.
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The ashes were first mixed with a brine solution (L/S ratio of 5 L kg-1) for 2 h and sieved at 38 µm. The brine solution (pH 11.5) came from previous ash washings. The fraction below 38 µm was recovered and washed with water to remove the main soluble salts (NaCl, KCl). The residues were then carbonated in solution, by adding Na2CO3 or by injecting pure CO2 by means of a sintered glass vessel. Na2CO3 concentration was equivalent to twice the Ca molar concentration. The mixing with Na2CO3 in solution lasted 2 h, while the injection of CO2 took 20 min at a flow of 0.5 L min-1. The effects of carbonation were compared with simple washing by water. The different treatments were labelled H2OH2O, H2O-Na2CO3 and H2O-CO2.
Analysis methods The solid composition was determined by X-ray fluorescence (XRF) (Siemens RS 3000, Be source, Rh-anti-cathode, OVO 55 analyser crystal). Thermo gravimetric analyses (TGA) were carried out on samples of ashes to measure their CO2 content. The samples were heated to 850 °C at a constant rate of 10 °C min-1. The crystalline phases were identified using a Siemens D5000 powder X-ray diffractometer equipped with a monochromator using a cobalt anticathode (λ = 1.789 Å). Quantitative analyses were performed using a CAMECA SX50 microprobe with SAMx automation. The operating conditions were: accelerating voltage 15 kV, beam current 10 nA and analysed surface approximately 3 µm × 3 μm. Natural and synthetic minerals were used as standards. Detection limits for Zn and Pb are 0.3 and 0.4%, respectively. Leaching tests were applied to residues mixed with deionized water (L/S = 10 L kg-1) for 24 hours in a rotary agitation device (EN 12457-2, 2002). Solutions were then filtrated on 0.45 µm-membranes (Millipore). Cr, Cu, Pb and Zn concentrations were analysed by Inductively Coupled Plasma Optical Emission Spectroscopy (ICP-OES, Varian VISTA-MPX CCD Simultaneous). Chlorides were qualitatively estimated by chloride titrators (Hach).
Results and discussion Chemical composition Raw ESP fly ashes and treatment residues contain Ca as a major cationic component (expressed as CaO), as shown in Table 2. The concentration of CaO increases after the treatment, mainly because of the dissolution of soluble salts (NaCl, KCl expressed as Cl, Na2O and K2O in Table 2), but also because of the formation of calcite, especially in the H2O-Na2CO3 treatment. The fluctuations in S (as SO3) concentration are also noteworthy; in case of the H2O-Na2CO3 treatment, the SO3 concentration dropped to 2.9%, reflecting the reaction of anhydrite with Na2CO3 according to: Na2CO3 + CaSO4 → Na2SO4 + CaCO3. This reaction produced soluble sodium sulphate, which then dissolved in the washing water, and calcite (CaCO3). The carbonation effect of H2O-Na2CO3 and H2O-CO2 treatments was highlighted by the
Table 2. Chemical composition of raw ESP and treated residues, in oxides (%). %
Raw
H2O-H2O
H2O-Na2CO3
H2O-CO2
CaO Cl SO3 Na2O K2O SiO2 Al2O3 CO2 ZnO P2O5 TiO2 MgO Fe2O3 PbO SnO2 Br CuO Sb2O3 BaO Cr2O3 MnO
22.2 20.0 14.1 13.5 8.4 7.6 3.7 2.2 2.0 1.9 1.3 1.1 0.89 0.42 0.14 0.13 0.10 0.10 0.08 0.08 0.04
36.3 0.4 22.3 0.3 1.1 12.0 6.2 4.0 5.9 4.0 1.9 1.5 0.8 0.81 0.28 n.d. 0.18 0.19 0.17 0.44 1.1
44.5 0.7 2.9 2.4 0.8 14.5 5.7 7.9 6.9 4.5 2.4 2.7 1.8 0.87 0.33 n.d. 0.24 0.22 0.20 0.23 0.09
34.2 0.7 16.5 0.6 0.9 13.8 7.3 6.0 7.0 4.5 2.1 2.6 1.5 0.99 0.25 n.d. 0.33 0.15 0.20 0.21 0.08
n.d.: non detected.
increase in the CO2 content of the ashes. Heavy metals, especially Zn, appeared to be generally more concentrated in the treated residues, because these residues correspond to the solid fraction below 38 µm richer in heavy metal compounds (De Boom & Degrez, 2009), as these compounds preferably condense on small particles (Chandler et al., 1997).
Mineralogy Thirteen mineralogical compounds in raw ESP fly ashes were identified by X-ray diffraction (XRD) (Figure 1). Among those compounds, chlorides (halite and sylvite) were the most abundant. After treatment, the chloride salts were removed from the solids because of their high solubility (see Figure2). Residues from H2O-H2O and H2O-CO2 treatment mainly consisted of anhydrite and calcite, while H2O-Na2CO3 residues only contained calcite. The absence of anhydrite in H2O-Na2CO3 residues may be owing to the transformation of anhydrite into calcium carbonate, which is a thermodynamically more stable component (Fernández-Díaz et al., 2010). The precise calcium carbonate mineral formed (calcite or vaterite, CaCO3) depends on the ratio between CO32- and SO42- anions: if SO42-/CO32- > 1, vaterite forms while, if the ratio is < 1, calcite precipitates, as was the case in the present work (Fernández-Díaz et al., 2010). Some microprobe analyses were conducted on the treatment residues to complete the mineralogical characterization performed by XRD. Table 3 summarizes the different compounds identified by XRD and microprobe. Over 100 spots were analysed by microprobe for H2O-H2O and H2O-CO2 residues, while only 50 were
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De Boom et al.
Figure 1. Raw ESP fly ashes – XRD diffractograms.
Figure 2. Treatment residues – XRD diffractograms.
taken for H2O-Na2CO3 residues because of the massive presence of aggregates in which individual particles were not easy to distinguish from the resin. As the technique does not identify H or C, hydrated and carbonated compounds were expected to present a deficit in their analysis (total largely below 100%). Microprobe
analyses confirmed the presence of perovskite and hematite, which was only supposed from XRD study owing to the significant overlapping of diffraction peaks. Moreover, microprobe analyses also indicated the scarcity of quartz in all the treatment residues. As the residues have been sieved at 38 µm, their small size may explain
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Table 3. Mineral compounds present in the different residues – XRD and microprobe analyses. Raw H2O- H2OH2OH2O Na2CO3 CO2 Quartz Anhydrite Bassanite Gehlenite Portlandite Calcite Perovskite Halite Sylvite Hydrocalumite Hematite Hydroxylapatite
SiO2 CaSO4 CaSO4.0.5H2O Ca2Al2SiO7 Ca(OH)2 CaCO3 CaTiO3 NaCl KCl Ca4Al3O6Cl2.10H2O Fe2O3 Ca5(PO4)3OH
X X X X X X X X X X X X
X X X X
X
X X
X X
X X
X X
X
X X X X X X X X
the scarcity of quartz (Bodénan et al., 2010; Thipse et al., 2002). Finally, a few minerals rich in K were measured in the raw sample and could correspond to feldspars, such as microcline, which it was not possible to identify using XRD analyses because of the number of minerals contained by the ash and the low concentration of this phase.
Pb and Zn speciation The microprobe analyses also identified some particles or aggregates presenting higher levels of heavy metals, especially Zn and Pb. The 250 analyses conducted on the three treated ashes seemed to show that Zn contamination was rather diffuse in the different residues. However, a few particles containing more than 5% ZnO were detected (see Table 4). Particles presenting such high concentrations in heavy metal compounds may determine the hazardous character of the residue. The particle matrix generally consisted of CaO, while some analyses revealed high levels of SiO2 or SO3 in some particles. In H2O-H2O residues, high concentrations of ZnO may also have been associated with the presence of MgO (one particle containing 36% of other compounds, mainly MgO in this case). In H2O-Na2CO3 residues, ZnO seemed to be linked with higher concentration of Fe2O3 or SiO2. The H2O-CO2 residues presented the highest ZnO levels, associated with relatively high concentrations of SiO2 and Al2O3. Some TiO2 rich particles were also visible. As for Zn, some Pb-rich particles were also identified (see Table 5). The particles systematically presented CaO, SO3 and ZnO. In H2O-Na2CO3 and H2O-CO2 residues, TiO2-rich particles were also detected. These results showed that the ash contamination in Pb and Zn was diffuse, whatever the ash treatment. So, the treatments did not influence the Pb and Zn speciation.
Leaching behaviour The leaching tests showed that all the treatments efficiently removed the chlorides (see Table 6). The washing with water only
led to the extraction of amounts above the non-hazardous waste limits for landfilling in the case of Pb (2003/33/EC). The carbonation using Na2CO3 reduced the leaching of Pb and thus allowed the residue to be considered as a non-hazardous material, even though Cr and Zn leaching increased slightly with this treatment compared with washing using water only. In the same way, bubbling with gaseous CO2 considerably improved the Pb and Zn leaching, their extracted amounts becoming undetectable. With such treatment, the chromium leaching increase prevented the residue from being considered as a non-hazardous material. The results presented in this article are comparable with those found in the literature (Table 1): carbonation leads to a decrease in Pb and Zn leaching that may be directly related to the pH falling to just below 11, where Pb and Zn compounds can precipitate (Van Herck et al., 2000). The carbonation increased the leaching amount of Cr. According to Baciocchi et al. (2007), the increase could be related to the fact that the pH decreased in the case of H2O-CO2, where the Cr leaching increase was more marked. However, it is rather difficult to explain the Cr leaching behaviour. Astrup et al. (2005) studied Cr leaching from APC residues, considering that Cr is mainly present as Cr(VI). At the contrary, Cr(III) has been principally found in MSWI fly ash by Hu et al. (2013), which is reinforced by the low leaching of Cr from fly ash, compared with bottom ash, related by Verbinnen et al. (2013) and by the small proportion of leached Cr compared with the total context (8.95%) indicated by Chiang et al. (2009). By assuming that Cr is mainly present as Cr(III) in the initial residues, a leaching increase may be due to oxidation of Cr(III) to Cr(VI) being more soluble. Verbinnen et al. (2013) proved by thermodynamics and kinetics that the oxidation of Cr(III) by O2 in the presence of alkali is favoured, which could have thus happened during the carbonation experiments of the present study.
Conclusion The effect of carbonation on the mineralogy of MSWI electrofilter (ESP) fly ashes and on the leaching of heavy metals was investigated in this work. Carbonation was achieved either by Na2CO3 mixing or by CO2 bubbling in water. All the carbonation treatments led to the dissolution of chlorides (NaCl, KCl), the formation of carbonate compounds (mainly calcite) and, in the case of Na2CO3 mixing, anhydrite removal. Pb and Zn speciation was studied using microprobe analysis to identify possible effects of the carbonation treatments on the stabilization of the elements in some specific phases. Microprobe analyses of the residues obtained with the three treatments under study (washing with water only, Na2CO3 addition and CO2 bubbling) were comparable and Pb and Zn contamination appeared to be rather diffuse. Thus, microprobe analyses did not highlight all the effects of the various treatments on the speciation of Pb and Zn in the residues. In spite of this, the results of the leaching tests carried out on the three residues showed significant differences. The carbonation using Na2CO3 decreased the leaching of Pb compared with the washing with only water and thus permitted
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De Boom et al. Table 4. Oxide compounds (%) detected in particles containing more than 5% in ZnO – microprobe analyses (‘Other’ corresponds to the sum of K2O, MgO, Na2O and P2O5). %
Total
CaO
SiO2
Al2O3
SO3
TiO2
Fe2O3
ZnO
PbO
Other
H2O-H2O H2ONa2CO3 H2O-CO2
98.0 59.4 76.3 38.0 28.8 34.1 33.0 36.0 39.7 23.4 69.5 72.8 89.4 95.8 83.6 101.1 34.4 90.3 50.4 46.8 40.6 32.9 40.1 36.6 32.6
35.2 8.1 15.1 12.8 9.4 7.0 12.0 12.4 16.2 7.1 41.5 6.3 7.0 22.7 28.2 16.5 12.3 25.7 9.3 18.9 12.0 9.4 12.5 13.9 10.3
45.9 28.7 0.7 5.6 2.5 6.8 3.2 3.8 5.3 2.7 6.5 7.9 5.5 31.5 39.1 37.2 5.9 22.2 11.5 9.9 9.7 5.1 5.6 5.9 5.8
6.3 4.3 0.3 2.1 1.1 5.3 1.7 2.4 2.0 1.4 0.2 3.7 2.3 23.4 2.8 9.5 2.1 14.4 7.0 7.1 5.1 2.6 2.4 3.2 3.3
0.3 4.4 16.6 5.5 5.1 4.9 4.7 4.3 3.8 2.6 2.2 0.1 0.1 0.1 0.1 0.0 3.1 0.8 3.1 1.2 4.3 4.8 3.3 2.1 3.5
0.2 1.5 0.1 0.0 0.0 0.5 1.3 0.1 0.4 0.0 6.2 0.2 0.4 0.4 0.4 6.1 1.9 0.2 0.6 0.9 0.3 0.5 0.1 0.1 0.2
0.4 0.3 0.5 0.7 0.2 0.2 1.1 0.3 0.4 0.2 0.1 34.5 63.7 1.0 1.8 0.9 0.7 0.5 0.8 0.2 0.6 0.3 0.5 0.5 0.8
5.0 7.8 6.8 8.5 7.3 8.2 5.2 9.9 6.4 5.1 7.4 17.5 5.9 8.2 5.7 7.4 5.5 22.5 13.1 5.4 5.4 7.0 6.7 6.1 5.9
0.3 0.3 0.2 0.7 0.5 0.2 0.6 0.7 0.6 0.2 3.9 0.1 0.1 0.2 0.4 0.1 0.6 0.4 1.1 1.1 0.5 1.1 0.5 1.1 0.8
4.2 4.1 36.0 2.2 2.7 1.1 3.2 2.1 4.5 4.2 1.4 2.5 4.4 8.3 5.0 23.5 2.3 3.6 3.8 2.1 2.7 2.0 8.6 3.8 2.0
Data in bold indicate higher concentrations.
Table 5. Oxide compounds (%) detected in particles with more than 0.8% in PbO – microprobe analyses.
H2O-H2O H2ONa2CO3 H2O-CO2
Total
CaO
SiO2
Al2O3
SO3
TiO2
Fe2O3
ZnO
PbO
Other
70.2 54.5 46.2 86.7 52.6 56.3 53.0 42.2 37.1 26.8 63.6 40.5 20.6 82.6 41.0 50.5 41.3 54.4 35.9 26.9 21.7 25.4
29.8 19.9 20.9 52.1 22.4 48.9 46.5 18.1 16.5 11.7 33.0 23.5 6.0 39.6 17.1 28.1 18.2 28.9 11.8 15.4 5.8 4.5
2.1 4.2 2.9 20.3 11.3 1.2 0.9 3.4 3.2 3.5 7.2 5.9 5.8 15.4 2.8 5.4 3.7 7.7 7.1 2.4 5.3 6.3
1.2 2.7 5.7 0.5 3.6 0.2 0.1 4.3 1.1 1.5 2.3 1.3 1.3 2.2 2.6 5.1 1.7 5.7 3.4 1.2 2.6 3.6
27.6 19.8 11.8 8.9 6.5 1.9 1.8 8.5 5.2 3.7 4.2 1.3 0.6 11.9 9.9 8.9 2.6 5.2 4.0 3.3 1.1 1.0
1.3 0.3 2.3 1.1 0.1 0.1 0.1 3.2 0.0 0.1 11.4 0.8 0.1 0.5 0.0 0.0 9.5 1.1 0.7 0.0 0.2 0.2
0.4 0.3 0.1 0.1 0.4 0.1 0.3 0.7 0.4 0.4 0.8 2.8 0.6 3.5 0.2 0.2 0.5 0.5 0.6 0.3 0.4 0.6
1.3 3.8 1.2 1.9 3.2 2.1 1.5 1.9 4.8 3.3 2.0 2.2 2.4 2.1 4.6 1.0 2.8 2.3 4.4 2.3 3.9 4.7
0.8 0.9 0.9 0.9 3.0 1.1 1.2 0.8 1.0 0.8 0.8 0.9 0.8 1.2 1.4 1.2 0.9 1.4 0.9 0.8 0.9 1.0
5.7 2.7 0.4 1.0 2.0 0.7 0.6 1.2 4.7 2.0 1.8 2.0 3.0 6.2 2.3 0.6 1.5 1.7 3.1 1.2 1.6 3.6
Data in bold indicate higher concentrations.
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Table 6. Amounts of Cl (g kg-1), Cr, Cu, Pb and Zn (mg kg-1) extracted and pH after the leaching test, compared with European limits for landfilling (2003/33/EC). Cl
Cr
Cu
g kg-1 mg kg-1
H2O-H2O H2O-Na2CO3 H2O-CO2 Hazardous waste limit Non-hazardous waste limit
0.3 0.2 0.2 25 15
