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Characterization of soluble and insoluble radioactive cesium in municipal solid waste incineration fly ash
Chemosphere 248 (2020) 126007
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Characterization of soluble and insoluble radioactive cesium in municipal solid waste incineration fly ash Atsushi Ohbuchi a, *, Kengo Fujii b, Miki Kasari b, Yuya Koike c a
Rigaku Americas Corporation, 9009 New Trails Drive, The Woodlands, Texas, 77381, USA Applied Chemistry Course, Graduate School of Science and Technology, Meiji University, 1-1-1 Higashimita, Tama-ku, Kawasaki, 214-8571, Japan c Department of Applied Chemistry, School of Science and Technology, Meiji University, 1-1-1 Higashimita, Tama-ku, Kawasaki, Kanagawa, 214-8571, Japan b
h i g h l i g h t s Radioactive Cs in MSWI fly ash was separated into soluble and insoluble forms. The result of Tessier method indicated that water-soluble radioactive Cs exists as CsCl. Insoluble radioactive Cs was trapped into silicate as amorphous phase result from chemical treatment. Silicate-bound and free radioactive Cs were contained into surface and inner part of the silicate amorphous phase.
a r t i c l e i n f o
a b s t r a c t
Article history: Received 11 October 2019 Received in revised form 18 January 2020 Accepted 21 January 2020 Available online 22 January 2020
Soluble and insoluble radioactive cesium in municipal solid waste incineration fly ash were analyzed by X-ray diffraction and gamma-ray spectrometry. A total of 60% of soluble radioactive cesium was determined using the Tessier extraction method, and it was almost same extraction rate with Japanese leaching test No.13. In addition, chloride compounds such as halite (NaCl) and sylvite (KCl) showed same behavior with soluble radioactive cesium, therefore, soluble radioactive cesium existed as a chloride (CsCl) with water solubility characteristics. Almost insoluble radioactive cesium trapped into silicate of crystalline phase or amorphous phase was eluted by hydrogen fluoride treatment. Radioactive 137Cs was released in three stages by heating treatment (untreated - 400 C, 600 Ce800 C, and 800 Ce1000 C) according to decreasing amorphous content. The relationship between the concentrations of radioactive 137 Cs and amorphous phase exhibited good linearity (R ¼ 0.9278). Insoluble radioactive 137Cs was contained in inner part of the amorphous phase, and free radioactive cesium was determined from the concentration of the amorphous phase. © 2020 Elsevier Ltd. All rights reserved.
Handling Editor: Martine Leermakers Keywords: Municipal solid waste incineration fly ash Soluble and insoluble radioactive cesium Tessier extraction method Chemical treatment Heating treatment
1. Introduction Considerable amounts of radioactive cesium having 11.8e18 PBq (134Cs) and 13e62.5 (137Cs) PBq (Steinhauser et al., 2014) were released into environment by the Fukushima Daiichi Nuclear Power Plant (FDNPP) accident. After the FDNPP accident, the concentration of radioactive cesium in soil near Kawasaki, located 300 km from the FDNPP, increased by a factor of ˃100 (Ochi et al., 2017). Moreover, the radioactive cesium concentration in waste collected at Kyusyu, located approximately 1200 km from FDNPP, was 5
* Corresponding author. Tel.: þ1 281 362 2300; fax: þ1 281 364 3628 E-mail addresses: [email protected], [email protected] (A. Ohbuchi). https://doi.org/10.1016/j.chemosphere.2020.126007 0045-6535/© 2020 Elsevier Ltd. All rights reserved.
times higher than the levels measured before the accident (Iwahana et al., 2013). Eight years after the FDNPP accident, radioactive cesium can be detected in high concentrations due to the long half-lives of 134Cs and 137Cs (T1/2 ¼ 2.06 and 30.07 years, respectively). The deposited radioactive cesium on the ground via dry and wet deposition were incinerated at an incineration plant to reduce the waste volume. After incineration, municipal solid waste incineration (MSWI) fly ash and bottom ash were produced, and both ashes were buried in landfills after stabilization treatment to prevent the elution of toxic components. The Ministry of the Environment Government of Japan has reported radioactive cesium in contaminated materials is contained in the fly and bottom ashes to fairly high concentrations, and a higher concentration of radioactive cesium in MSWI fly ash compared to that in MSWI bottom ash
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(Ministry of the Ministry of Environment, 2011). The limit for radioactivity set by Japanese Ministry of the Environment is ˂8000 Bq kg1 in waste materials including fly ash. Radioactive waste is incinerated as usual waste material, and the generated ashes are subsequently stored in landfills. Waste materials with radioactivities of ˃8000 Bq kg1 are treated to control the radioactivity of the landfill site by enclosing around with soils of a water resistant layer to prevent contact with water, and putting an absorption layer of radioactive materials at underside (Ministry of the Ministry of the Environment Government of Japan, 2015). In contrast, fly ash with ˂8000 Bq kg1 can be recycled for uses in cement (Aubert et al., 2006; Saikia et al., 2007), ceramics (Qian et al., 2006), stone (Nishida et al., 2001), and zeolite (Fan et al., 2008), similar to regular MSWI fly ash. The physicochemical properties of fly ash were investigated by conducting leaching tests of heavy metals (Harada et al., 2011; Okada and Matsuto, 2009). Lead in fly ash was specified by sequential chemical extraction (Sukandar et al., 2009), leaching of Cu, Cr, and Pb were suppressed by ball milling (Chen et al., 2016). Moreover, enrichment and distribution of heavy metals were et al., 2017). However, the physicochemical investigated (Raclavska properties of radioactive nuclides are required for further comprehensive understanding of fly ash characteristics. Studies regarding the speciation analyses of radioactive cesium in fly ash have been reported after the FDNPP accident (Saffarzadeh et al., 2014; Tojo et al., 2014; Shiota et al., 2015; Iwahana et al., 2017). Iwahana (Iwahana et al., 2017) and co-workers reported the chemical speciation of 210Pb using the sequential extraction method proposed by Tessier (Tessier et al., 1979), and the chemical form differed from that of stable Pb. An insoluble radioactive cesium in bottom ash was contained to the amorphous matter (Tojo et al., 2014). The chemical form of radioactive cesium could be separated into water-soluble and insoluble forms using the Japanese leaching test No. 13 (JLT-13) defined by the Ministry of the Environment Government of Japan. The JLT-13 can be applied to MSWI fly ash to determine the leaching properties of metals (Sakai et al., 1995; Pariatamby et al., 2006). The physicochemical properties of radioactive cesium in fly ash were also studied using the JLT13 (Ohbuchi et al., 2016; Fujii et al., 2018). Approximately 60% of radioactive cesium was present as water-soluble forms in fly ash (Ohbuchi et al., 2016). Moreover, the elution ratio of radioactive cesium from fly ash increased with decrease in the particle size and was influenced by the presence of chloride compounds such as sodium chloride (NaCl) and potassium chloride (KCl). Therefore, radioactive cesium in fly ash is likely contained as chloride compounds such as CsCl (Fujii et al., 2018). Estimation of the chemical forms of radioactive cesium in fly ash is useful for the safe recycling and control of landfilled fly ash. Herein, characteristic of radioactive cesium in MSWI fly ash contaminated by the FDNPP accident was evaluated. Especially, estimation of the chemical form of insoluble radioactive cesium in the amorphous phase was performed, including quantitative analysis of the amorphous phase by Rietveld refinement (Rietveld, 1969) which was applied to various materials such as cement (Guirado et al., 2000; Taylor et al., 2000), and waste materials (Singh and Subramaniam, 2016; Ohbuchi et al., 2019). The sequential extraction method developed by Tessier was used to further evaluate the form of soluble radioactive cesium. Moreover, the chemical speciation of insoluble radioactive cesium was evaluated considering the relationship between the concentrations of radioactive cesium and amorphous phase by chemical and heat treatments.
2. Materials and methods 2.1. Sample preparation MSWI fly ash samples, which was same sample with previous study (Ohbuchi et al., 2016), were collected from a municipal waste incineration plant in Fukushima Prefecture, Japan, on January 2013 and dried at 105 C for 24 h. The combustion capacity of plant is 300-ton day1 with two stoker furnaces in the plant at temperature between 800 and 1000 C where municipal solid waste (MSW) of general component is combusted. The bottom ash was composed of cinder cooled with water. The fly ash was collected from an electrostatic precipitator after spraying with slaked lime to neutralize acid gases. About one kg of fly ash was fractionated to 20 g by conical quartering. The activity ratio of radioactive nuclides 134 Cs/137Cs in MSWI fly ash derived from the FDNPP accident was previously determined to be 1:1 (Komori et al., 2013) and the behavior of 134Cs is similar to that of 137Cs (Saffarzadeh et al., 2014). The activity ratio of 134Cs/137Cs in all samples was decay-corrected on March 11, 2011, the day of the FDNPP accident. Gamma-ray spectrometry indicated that the radioactive cesium in the fly ash originated from the FDNPP accident. 2.2. Gamma-ray spectrometry The activity of radioactive cesium was determined via gammaray spectrometry using a p-type high-purity Ge/coaxial-type semiconductor detector (HPGe; IGC 10200, Princeton Gamma Tech Instruments, Inc., USA) surrounded by a 100 mm-thick lead shield with 50 mm-thick oxygen-free copper and 5 mm-thick acrylic plates. Each of the classified fly ash samples was compressed in the U8 container (height and diameter of 68 and 56 mm, respectively, Sekiya Rika Co. Ltd, Japan). Detection efficiencies were calculated for gamma ray spectrum of a152Eu standard source (diameter and height of 25 and 6.0 mm, respectively, Japan Radioisotope Association, Japan). The detection efficiency curve drawn using detection efficiencies of standard source was corrected using the 1461 keV gamma-ray activity emitted from 4 K in KCl (Koike et al., 2017; Fujii et al., 2018). Koike et al. (2017) have developed a gamma-ray spectrometry calibration method using natural radionuclides included in commercially available chemical regents at a noncontrolled area in Japan. The activities of 134Cs and 137Cs were determined by the emitted gamma rays, i.e., 606 and 662 keV, respectively. 2.3. X-ray diffractometry A SmartLab diffractometer (Rigaku, Japan) equipped with a horizontal goniometer in Bragg-Brentano para-focusing geometry and CuKa1,2 (2 kW X-ray tube) with a one-dimensional silicon strip detector D/teX Ultra250 were used for crystalline phase analysis. The samples were loaded into a glass sample holder by samplefront-pressing. The diffraction patterns of the samples were recorded from 5 to 80 /2q at 0.01 intervals and at a 2 /min scanning speed. Phase identification and quantitative analysis by Rietveld refinement were performed using the integrated X-ray powder diffraction software PDXL (Rigaku, Japan). 2.4. X-ray fluorescence spectrometry The major and minor elements in fly ash were analyzed using a Rigaku ZSX Primus IV (Rigaku, Japan) X-ray fluorescence spectrometer equipped with an end window containing a 4 kW Rh Xray tube. The analyzer crystals were LiF(200), Ge(111), PET(002), and RX25. A NaI scintillation counter and proportional counter with
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flowing P-10 gas composed of Ar (90%) and CH4 (10%) were used as detectors. The gas flow rate of the P-10 gas was 50 cm3 min1. 2.5. Rietveld refinement
3
(i) Ion exchangeable fraction Five g of fly ash was leached for 1 h at 25 C with continuous agitation using 40 mL of 1 mol L1 magnesium chloride (MgCl2, Junsei Chemical Co. ltd, Japan).
Pattern fitting was performed using PDXL software and was based on Rietveld method. Rietveld refinement was applied over the entire diffraction profile (for example 5e90 /2q). The background for each pattern was defined as the interpolation of n points that were manually introduced. The profile function used a split pseudo-Voigt function (Toraya, 1990) to consider the asymmetry of each peak. The optimized parameters were: background coefficients, peak shift, lattice constant, full width at half maximum (FWHM), and peak shape. The quantitative values of each crystalline phase were calculated as follows:
Forty mL of 1 mol L1 sodium acetic acid buffer (pH 5) prepared using sodium acetate (CH3COONa, Junsei Chemical Co. ltd, Japan), acetate acid (CH3COOH, Junsei Chemical Co. ltd, Japan), and distillated water was added to the residues from step (i) for 6 h at room temperature to leach carbonate bound materials.
ðS Z M V Þ W i ¼ P i i i i j Sj Zj Mj Vj
The free oxide phases were extracted using 100 mL of 0.04 mol L1 of hydroxylamine hydrochloride (NH2OH HCl, Wako Pure Chemical Co., Japan) heated at 96 C for 6 h.
(1)
In Eq. (1), Wi is the weight fraction of the analyte crystal i, S is the scale factor after the Rietveld refinement, Z is the number of molecules in a unit cell, M is the molecular weight, and V is the unit cell volume derived from the lattice constant. The concentration of amorphous phase was calculated using the following equations via the external standard method (O’Connor and Raven, 1988) using corundum (a-Al2O3: Kojyundo Chemical Laboratory Co. Ltd, Japan):
G ¼ SCor
rCor V 2Cor m*Cor CCor
(2)
In Eq. (2), SCor is the Rietveld scale factor for corundum, rCor is the corundum density, VCor is the corundum unit-cell volume, CCor is the corundum weight fraction (100 mass%), and m*Cor is the corundum mass absorption coefficient. The G factor was obtained using a pure standard material with high crystallinity. The concentration of the crystalline phase i was calculated using the following equation by substitution of the G factor.
C i ¼ Si
ri V 2i m*sample G
100
X
Ci
(iii) Free oxide fraction
(iv) Bound to organic matter fraction The residue of step (iii) was agitated in 25 mL of hydrogen peroxide (H2O2, Junsei Chemical Co. ltd, Japan) and 15 mL of 0.02 mol L1 nitric acid at 85 C for 3 h. After treatment, 25 mL of 3.2 mol L1 ammonium acetate (CH3COONH4, Wako Pure Chemical Co.), 20 mL of distillated water, and 15 mL of 0.02 mol L1 nitric acid were added and stirred to extract organic and sulfide matter for 3 h at 25 C. (v) Residue fraction The solid material remaining after step (iv) was referred to as the residual materials. The raw fly ash and four residues from extraction steps (i)e(iv) were analyzed by powder XRD to determine the speciation of the crystalline and amorphous phases, and gamma-ray spectrometry was performed for analysis of radioactive nuclides. 2.7. Chemical treatment
(3)
In Eq. (3), Ci is concentration of the crystalline phase i, Si is the Rietveld scale factor of the crystalline phase i, ri is the crystalline phase i density, Vi is unit-cell volume of the crystalline phase i, and m*sample is the mass absorption coefficient of the sample. The m*sample value was calculated from elemental analysis by X-ray fluorescence spectrometry. The concentration of amorphous phase CAmo is calculated by the following equation (4).
CAmo ¼ 100
(ii) Carbonate bound fraction
(4)
2.6. Sequential extraction via the tessier extraction method The sequential extraction via the Tessier extraction method was used to determine the speciation of the radioactive nuclides in MSWI fly ash. This method is often used to determine the speciation of heavy metals in soil and sediment samples (Abollino et al., 2002; Rosado et al., 2016) and the fractions can be classified into five phases; ion exchangeable (IE), carbonate bound (CB), FeeMn oxide (OX), bound to organic matter (OB), and residual (Res) fractions using the appropriate extraction reagents. The extraction method used herein included the following steps.
The JLT-13 specifies that a mixture (S/L ¼ 0.1) of 50 mL of pure water (pH ¼ 6.20) and MSWI fly ash dried by 105 C for 24 h should be subjected to continuous shaking for 6 h at 25 C. A mechanical shaker (Shaking Bath TBK 602DA, Advantec Inc., Japan) was used to prepare the eluted solutions from fly ash. The shaker velocity was approximately 200 rpm. After shaking, the eluted solutions were separated using filter paper (Whatman™ glass microfiber filters, 100 circles, GE Healthcare Life Science, USA). Each chemical treatment for dissolving the insoluble radioactive cesium in amorphous phase of MSWI fly ash was carried out as the following procedures. MSWI fly ash after the JLT-13 treatment was used for each chemical treatment. (a): Nitrohydrochloric acid derived from nitric acid (HNO3, Junsei Chemical Co. ltd, Japan) and hydrochloric acid (HCl, Junsei Chemical Co. ltd, Japan). Twenty mL of nitrohydrochloric acid of pH 1e5 used for evaluation in acid region was added to 1 g of MSWI fly ash, and the mixture was heated at 100 C for 6 h. (b): Sodium hydroxide (NaOH, Wako Pure Chemical Co., Japan). Twenty mL of sodium hydroxide solution was added to 1 g of MSWI fly ash, and the mixture was stirred for 6 h. (c): Hydrogen fluoride (HF, Wako Pure Chemical Co., Japan). Eighty mL of nitric acid and 20 mL of hydrogen fluoride were added to 5 g of MSWI fly ash, and the mixture was heated at 95 C
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for 6 h. Each eluted solution was separated using a filter paper, and then filtered solutions were separated to obtain residues and elutions via centrifugation at 3000 rpm for 20 min. Each eluted solution was heated immediately to evaporate the solvent for dryness. All ashes were ground by a hi-speed vibrating sample mill (TI-100, CMT Co., Ltd., Japan) before measurement. 2.8. Heat treatment MSWI fly ashes after the JLT-13 were heated using a muffle furnace (KDF S-70, Denken-Highdental Co., Ltd., Japan) at 400, 600, 800 and 1000 C for 24 h to release insoluble radioactive cesium in amorphous phase by crystallization. 3. Results and discussion 3.1. Crystal morphology in sequentially extracted MSWI fly ash XRD analysis was conducted to investigate the matrix and crystalline phase of the MSWI fly ash since crystalline in the MSWI fly ash and varied by waste composition and incineration conditions used in the incineration facility. Also, speciation of soluble radioactive cesium was estimated as chloride compound by crystalline components in MSWI fly ash (Fujii et al., 2018). Therefore, crystalline phases contained in MSWI fly ash were investigated via XRD combined with the sequential extraction method. The X-ray diffraction patterns of each residue including raw MSWI fly ash are shown in Fig. 1. Anhydrite (CaSO4), biotite (KFeMg2Al3O10(H2O)2), calcium aluminum oxide (Ca3Al2O6), calcite (CaCO3), calcium chloride hydroxide (CaClOH), cordierite (Mg2Al4Si5O18), gehlenite (Ca2Al2SiO7), halite (NaCl), larnite (Ca2SiO4), portlandite (Ca(OH)2), quartz (SiO2), and sylvite (KCl) were identified from the diffraction pattern of raw MSWI fly ash. The crystalline phases differed compared to other MSWI fly ashes (Bogush et al., 2015; Funari et al., 2018; Ohbuchi et al., 2019). It is considered that components in MSWI fly ash were depending on MSW at
Fig. 1. X-ray diffraction patterns of raw MSWI fly ash and each extracted residue.(a) Raw MSWI fly ash, (b) IE fraction, (c) CB fraction, (d) OX fraction, and (e) bound to organic matter fraction residues. Alb: albite (NaAlSi3O8), Anh: anhydride (CaSO4), Bas: bassanite (CaSO4(H2O)0.5), Bio: biotite (KFeMg2(AlSi3O10(OH)2)), Cal: calcite (CaCO3), Cao: calcium aluminum oxide (Ca3Al2O6), Cch: calcium chloride hydroxide (CaClOH), Cor: cordierite (Mg2Al4Si5O18), Cri: cristobalite (SiO2), Etr: ettringite (Ca6(Al(OH)6)2(SO4)3(H2O)25.7), Geh: gehlenite (Ca2Al2SiO7), Hal: halite (NaCl), Hem: Hematite (Fe2O3), Lar: larnite (Ca2SiO4), Mag: magnetite (MgCO3), Ort: orthoclase (KAlSi3O8), Por: portlandite (Ca(OH)2), Qtz: quartz (SiO2), Rut: rutile (TiO2), Syl: sylvite (KCl), and Tob: tobermorite (Ca2.25Si3O5(OH)2(H2O)).
each region even if general municipal solid wastes (MSWs) were incinerated. Quartz is a major soil component, anhydride is a reaction product of SO2 and slaked lime in air, and calcite is a product of CO2 and slaked lime. Calcium chloride hydroxide, halite, and sylvite as chloride-containing compounds were likely derived from kitchen wastes including vegetables, seasonings, and plastics. Gehlenite and larnite are formed via crystallization of aluminosilicate by incinerating MSWs. After IE extraction, the diffraction peaks of the three chloride-containing compounds disappeared due to dissolution. Previously, chloride-containing compounds were dissolved in the JLT-13 using distillated water same with the IE fraction residue (Ohbuchi et al., 2016). In other words, IE and water extraction are considered to be similar extraction processes for chloride compounds such as halite, and sylvite in MSWI fly ash. After the sequential extraction, oxide compounds were identified in the diffraction pattern of the residue bound to the organic matter. The identified crystalline and amorphous phases in each residue and raw MSWI fly ash were calculated via Rietveld refinement combined with the external standard method (O’Connor and Raven, 1988). Table 1 shows the quantification results of the crystalline and amorphous phases. The amorphous phase concentration in MSWI fly ash was calculated to be approximately 30 mass%, and the amorphous phase concentration in each extraction residue increased relatively compared to that in the raw MSWI fly ash, reaching approximately 86 mass% in the final residue. The relationship between the amorphous phase and radioactive cesium is discussed in the next section in the context of evaluating the soluble and insoluble radioactive cesium. 3.2. Estimation of radioactive cesium crystal morphology The radioactivity concentration in raw MSWI fly ash was calculated by gamma-ray spectrometry. A radioactivity of approximately 5800 Bq kg1 was calculated as the total concentration of 134 Cs and 137Cs (Ohbuchi et al., 2016), which was below the regulation limit for landfilled wastes. However, investigating crystal morphologies of radioactive cesium are needed for a comprehensive understanding of the contaminated MSWI fly ash for recycling or landfilling even if radioactivity was below the regulation limit for landfilled wastes. In our previous research, soluble radioactive cesium was contained as chloride compound in MSWI fly ash, on the other hand, other crystal morphologies of radioactive cesium were not estimated. Therefore, crystal morphology of radioactive cesium was investigated by Tessier extraction method. The elution rate of radioactive cesium from MSWI fly ash at each fraction by the Tessier method is shown in Fig. 2. Similar elution behaviors were observed for radioactive 134Cs and 137Cs during each extraction process. Halite and sylvite of alkali metal chloride were dissolved during extraction of the IE fraction residue (Fig. 1), and 60% elution rate of radioactive cesium obtained by the IE fraction extraction was similar to that obtained using distilled water following the JLT-13 method (Fujii et al., 2018). It is considered that radioactive cesium dissolved by IE fraction was contained as chloride morphology (CsCl) having water-soluble characteristics in MSWI fly ash. In other words, almost same compounds were dissolved by distilled water used by the JLT-13 or magnesium chloride treatment used by IE fraction. The elution rates of radioactive cesium in the IE fraction were the highest at approximately 60% from the raw fly ash, whereas the elution rates in other fractions were ˂10% except for the CB fraction. Radioactive cesium in MSWI fly ash was separated into two crystal forms, namely, watersoluble or insoluble forms although water-soluble radioactive cesium was primarily contained as CsCl. For comprehending of insoluble radioactive cesium, relationship between elution rates of radioactive cesium and amorphous content was confirmed. Fig. 3
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5
Table 1 Concentrations of crystalline and amorphous phases in raw MSWI fly ash and each extraction fraction as determined by Tessier method. Crystalline phase
Concentration/mass%
Raw fly ash Anhydrite (CaSO4) Biotite (KFeMg2(AlSi3O10(OH)2) Calcium aluminum oxide (Ca3Al2O6) Calcium chloride hydroxide (CaClOH) Calcite (CaCO3) Cordierite (Mg2Al4Si5O18) Gehlenite (Ca2Al2SiO7) Halite (NaCl) Larnite (Ca2SiO4) Portlandite (Ca(OH)2) Quartz (SiO2) Sylvite (KCl) Amorphous
2.6 0.7 1.1 15.3 8.4 4.2 7.1 7.6 3.4 14.2 0.3 4.5 30.8
Residue of the CB fraction Bassanite (CaSO4(H2O)0.5) Brucite (Mg(OH)2) Calcite (CaCO3) Cordierite (Mg2Al4Si5O18) Gehlenite (Ca2Al2SiO7) Hematite (Fe2O3) Orthoclase (KAlSi3O8) Quartz (SiO2) Tobermorite ((CaO)5(SiO2)(H2O)5) Amorphous
3.2 12.9 14.2 1.1 13.2 0.7 1.7 1.9 0.9 49.1
Residue of the bound to organic matter fraction Albite (NaAlSi3O8) Cristobalite (SiO2) Hematite (Fe2O3) Magnetite (Fe3O4) Orthoclase (KAlSi3O8) Periclase (MgO) Quartz (SiO2) Rutile (TiO2) Amorphous
3.3 0.4 3.9 0.4 0.8 0.2 4.5 0.9 85.8
Crystalline phase
Concentration/mass%
Residue of the IE fraction Bassanite (CaSO4(H2O)0.5) Brucite (Mg(OH)2) Calcite (CaCO3) Gehlenite (Ca2Al2SiO7) Hematite (Fe2O3) Orthoclase (KAlSi3O8) Quartz (SiO2) Amorphous
2.1 10.4 10.3 5.7 0.8 0.8 2.1 67.8
Residue of the free OX fraction Albite (NaAlSi3O8) Cristobalite (SiO2) Ettringite (Ca6(Al(OH)6)2(SO4)3(H2O)26) Hematite (Fe2O3) Magnetite (Fe3O4) Orthoclase (KAlSi3O8) Periclase (MgO) Quartz (SiO2) Rutile (TiO2) Amorphous
1.1 1.0 0.5 4.3 0.7 0.6 0.7 4.3 1.0 86.1
radioactive cesium was decreased gradually since almost soluble radioactive cesium was dissolved by IE fraction. Therefore, the relationship between the elution rate of the soluble radioactive cesium and the amorphous content was shown as negative correlation. In the final residue, almost all insoluble radioactive cesium was contained among total radioactive cesium. Hence, the existence form of insoluble cesium in MSWI fly ash was considered to be trapped in the amorphous phase or combined with silicate. To evaluate the radioactive cesium trapped in the amorphous phase, chemical and heat treatments were applied.
3.3. Amorphous phase composition determination with the trapped insoluble radioactive cesium using chemical treatment
Fig. 2. Elution rate of radioactive cesium determined by the Tessier method. IE: Ion exchangeable fraction, CB: Carbonate bound fraction, OX: Free oxide fraction, OB: Bound to organic matter fraction, Res: Residue fraction.
shows the relationship of 134Cs and 137Cs in terms of their elution rates and amorphous content (good linearity; R ¼ 0.8). The amorphous content in raw MSWI fly ash was approximately 30 mass%, and the amorphous content increased to approximately 86 mass% relatively by extracting the soluble crystalline phases and radioactive cesium. On the other hand, the elution rate of the soluble
Insoluble radioactive cesium was considered to be primarily contained in the amorphous phase, although composition of amorphous phase was initially unknown. The amorphous phase composition with the trapped radioactive cesium was confirmed by chemical treatments. MSWI fly ash after the JLT-13 treatment to remove water-soluble radioactive cesium was chemically treated with hydrogen fluoride, nitrohydrochloric acid, and sodium hydroxide. Table 2 shows the elution rates of insoluble radioactive 137Cs from MSWI fly ash and the amorphous content in the residue with various chemical treatments. Insoluble radioactive 137Cs was confirmed because the 134 Cs content was excessively low. The elution rate of insoluble radioactive cesium by hydrogen fluoride treatment was shown largest value compared to the other chemical treatments. Table 3 lists the elemental compositions of the residues obtained after
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Fig. 3. Relationship between the elution rate of radioactive cesium and amorphous phase content.
Table 2 Elution rate of insoluble radioactive
137
Cs and amorphous phase after various chemical treatments.
Chemical treatment
Elution rate of the insoluble radioactive
JLT-13 Hydrogen fluoride Nitrohydrochloric acid (pH ¼ 1) Nitrohydrochloric acid (pH ¼ 3) Nitrohydrochloric acid (pH ¼ 5) NaOH (pH ¼ 10)
e 93.3 17.8 15.2 7.0 4.9
137
Cs/%
Amorphous phase content/mass% 67.1 39.4 26.6 21.3 21.3 27.4
Table 3 Elemental composition of MSWI fly ash residues after various chemical treatments. Element
Na2O MgO Al2O3 SiO2 P2O5 SO3 K2O CaO TiO2 Fe2O3
Concentration/mass% Hydrogen fluoride
Nitrohydrochloric acid (pH 1)
Nitrohydrochloric acid (pH 3)
Nitrohydrochloric acid (pH 5)
NaOH (pH 10)
1.4 2.3 12.1 3.2 0.1 0.6 0.1 76.1 1.1 2.5
1.3 2.1 9.4 18.0 1.4 2.5 0.3 58.1 2.1 1.6
1.3 1.9 7.7 15.8 1.2 3.9 0.3 61.8 1.9 2.0
0.5 1.7 7.6 15.5 1.2 4.0 0.3 63.0 1.9 2.0
1.0 1.9 7.9 15.8 1.2 4.4 0.3 61.6 1.9 1.9
each chemical treatment and Fig. 4 shows identification of crystalline phases in each residue. The SiO2 concentration after hydrogen fluoride treatment was shown lowest value, in contrast, it was maintained at approximately 15 mass% after the other chemical treatments. Also, diffraction peaks of quartz were disappeared and silicon was identified on the diffraction pattern of hydrogen fluoride treatment although diffraction peaks of quartz were observed on diffraction patterns of other chemical treatment residues. It is considered that silicates in amorphous phase and SiO2 of crystalline phase were dissolved only via hydrogen fluoride treatment, as a result, insoluble radioactive cesium contained into silicate phases was released. The elution rate obtained using nitrohydrochloric acid at each pH and sodium hydroxide treatments were lower than that obtained using hydrogen fluoride treatment although the amorphous phase contents decreased. The amorphous phases with other compositions such as Al2O3 and CaO differed from silicates were dissolved by nitrohydrochloric acid and sodium hydroxide treatments, although they did not almost
contain insoluble radioactive cesium, unlike the silicate amorphous phase. Therefore, the most of insoluble radioactive cesium was determined to be trapped in silicates of crystal or amorphous phases. 3.4. Heat treatment to release insoluble radioactive cesium from the amorphous phase A common approach for evaluating insoluble radioactive cesium involves crystallization of the amorphous phase by heating and determining the relationship between concentrations of radioactive cesium and amorphous phase. Water-soluble radioactive cesium in MSWI fly ash was extracted according to the JLT-13 protocol several times to evaluate only the insoluble radioactive cesium. The associated extraction residues were heated using an electric furnace at 400, 600, 800, and 1000 C. After each heating process, the concentration of radioactive cesium and amorphous phase were determined. Table 4 shows the
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Fig. 4. X-ray diffraction patterns of MSWI fly ash after JLT-13 (a) treated by (b) hydrogen fluoride, (c) nitrohydrochloride acid (pH ¼ 1), (d) nitrohydrochloride acid (pH ¼ 3), (e) nitrohydrochloride acid (pH ¼ 5), and (f) NaOH. And: andradite (Ca3Fe2(SiO4)O3), Anh: Anhydrite (CaSO4), Cal: calcite (CaCO3), Cao: calcium aluminum oxide (Ca3Al2O6), Cch; calcium chloride hydroxide (CaClOH), Geh: gehlenite (Ca2Al2SiO7), Chi: chiolite (Na5Al3F14), Cli: clinotobemorite (Ca5Si6O17(H2O)5), Hat: hatrurite (Ca3SiO5), Hem: hematite (Fe2O3), Heu: Heulandite-Ca (Ca2Al4Si14O36(H2O)12), Hyd: hydrocalumite (Ca2Al(CO3)0.25Cl0.5(OH)6(H2O)2.4), Kya: kyanite (Al2SiO5), Lar: larnite (Ca2SiO4), Ort: orthoclase (KAlSi3O8), Por: portlandite (Ca(OH)2), Qrz: quartz (a-SiO2), Rut: rutile (TiO2), Sil: silicon (Si), Tri: tridymite (SiO2).
analytical results regarding the concentration rate of insoluble radioactive 137Cs and amorphous phase. The amorphous phase content decreased gradually by heating and after 400 C heating, the amorphous phase and 137Cs contents decreased in same manner. The amorphous phase content in MSWI fly ash heated at 1000 C was 4.7 mass%, whereas that of unheated MSWI fly ash was 67.1 mass%. The amorphous phase was crystallized upon heat treatment, decreasing its concentration. Moreover, radioactive 137 Cs content was 24.8% after heat treatment at 1000 C. The decreased concentration of radioactive 137Cs was observed in three stages (untreated to 400 C, 600e800 C, and 800e1000 C), where the radioactive 137Cs content remained nearly constant between 400 and 600 C. Fig. 5 shows the X-ray diffraction pattern at each heat treatment temperature. Similar X-ray diffraction patterns were observed until heating at 600 C, however, the amorphous phase content decreased at 400 C heating along with that of radioactive 137Cs. Therefore, some radioactive 137Cs was trapped in the amorphous phase crystallized at low temperatures and the surface of the silicate amorphous phase can be crystallized by low temperature heating. After the 800 C heat treatment, the concentration of insoluble radioactive 137Cs decreased remarkably although the amorphous concentration showed almost the same value with 600 C heat treatment. Therefore, the decreased insoluble radioactive 137Cs content after 800 C heating was due to decreases in the free-radioactive cesium contained in amorphous released by 600 C heating boiling point of Cs is approximately 670 C). After the 1000 C heat treatment, a different X-ray
Table 4 Concentration rate of insoluble radioactive
7
Fig. 5. X-ray diffraction patterns of MSWI fly ash after JLT-13 heated at (a) unheated, (b) 400 C, (c) 600 C, (d) 800 C, and (e) 1000 C. And: andradite (Ca3Fe2(SiO4)O3), Anh: Anhydrite (CaSO4), Cal: calcite (CaCO3), Cao: calcium aluminum oxide (Ca3Al2O6), Cch; calcium chloride hydroxide (CaClOH), Dic: dicalcium diiron oxide (Ca2Fe2O5), Dol: dolomite (CaMg(CO3)2), Geh: gehlenite (Ca2Al2SiO7), Hat: hatrurite (Ca3SiO5), Hyd: hydrocalumite (Ca2Al(CO3)0.25Cl0.5(OH)6(H2O)2.4), Kat: katotite (Ca3Al2(O4H4)3), Lar: larnite (Ca2SiO4), Lim: lime (CaO), May: mayenite (Al14Ca12O33), Non: nonacalcium tris (Ca9(Al2O6)3), Oxy: oxyapatite (Ca10(PO4)6O), Por: portlandite (Ca(OH)2), Qrz: quartz (a-SiO2), Ter: ternesite (Ca5(SiO4)2(SO4)), and Xon: xonotlite (Ca6Si6O17(OH)2).
diffraction pattern was obtained compared to that at low temperature heating. A total of 6 crystalline (calcite, gehlenite, hatrurite (Ca3(SiO4)O), larnite (Ca2(SiO4)), mayenite (Ca12Al14O33), and quartz) phases were identified in the diffraction pattern up to the 600 C treated samples as common phases. In contrast, the 1000 C heated samples contained 13 crystalline phases (andradite (Ca3Fe2(SiO4)3), anhydride, dicalcium diiron oxide (Ca2Fe2O5), dolomite (CaMg(CO3)2), gehlenite, hatrurite, larnite, mayenite, lime (CaO), nanocalcium Tris (Ca9Al2O6)3), oxyapatite (Ca10(PO4)6O), and quartz) by forming new crystalline phases upon crystallization of the amorphous phase. The concentration rate of insoluble radioactive cesium decreased to 24.8% and that of the amorphous phase was 4.7 mass% after the 1000 C treatment. Insoluble radioactive 137 Cs trapped in the inner amorphous phase or amorphous phases of different compositions was released by crystallization at 1000 C. A high correlation coefficient of R ¼ 0.9278 was observed between concentration rate of insoluble radioactive 137Cs and amorphous phase in MSWI fly ash at each heating treatment (Table 4). Therefore, insoluble radioactive cesium was contained in MSWI fly ash in three forms: free-radioactive cesium and those trapped in the surface and inner portion of the silicate amorphous phase. 4. Conclusion Radioactive cesium in MSWI fly ash contaminated by the FDNPP accident was analyzed by XRD and gamma-ray spectrometry. A total of 12 crystalline phases were identified in the diffraction pattern of raw MSWI fly ash, and the chloride-containing
137
Cs and amorphous phase content at each heating temperature.
Heating temperature/ C
Concentration rate of insoluble radioactive
Unheated 400 600 800 1000
100 76.4 76.4 45.6 24.8
137
Cs/%
Amorphous phase content/mass% 67.1 42.0 26.3 21.8 4.7
8
A. Ohbuchi et al. / Chemosphere 248 (2020) 126007
compounds of halite and sylvite were dissolved via IE extraction using the sequential extraction method. In addition, approximately 60% of the radioactive cesium was dissolved in the IE fraction and was considered water-soluble radioactive cesium because the elution rate on IE fraction was similar to that obtained from the JLT13 with distilled water. The extraction rates of the other extraction fractions were quite low compared to the that of the IE fraction. Therefore, almost all soluble radioactive cesium was present in the form of chloride (CsCl) considering the elution behavior of chloride compounds. Radioactive cesium in MSWI fly ash could be separated to two forms, water-soluble as the chloride compound (CsCl) and insoluble forms. The insoluble radioactive cesium was confirmed using two approaches, chemical and heating treatments. The insoluble radioactive cesium composition in MSWI fly ash after the JLT-13 was confirmed using various chemical treatments. Insoluble radioactive cesium was eluted by hydrogen fluoride, and SiO2 concentration was significantly decreased. Therefore, almost insoluble radioactive cesium was contained primarily in silicate of amorphous or crystalline phases. MSWI fly ash after the JLT-13 was heated at several temperatures to determine the chemical form of the insoluble radioactive cesium. The relationship between the concentration rate of radioactive cesium and amorphous phase content in MSWI fly ash at each temperature exhibited good linearity (R ¼ 0.9278). The concentration rate of radioactive cesium was decreased in three distinct stages (untreated - 400 C, 600 Ce800 C, and 800 Ce1000 C) according to decreasing of amorphous content. Insoluble radioactive 137Cs was trapped into surface and inner part of the silicate amorphous phase as silicatebound and free radioactive cesium. This study provides a novel approach for the elution and removal of radioactive cesium for protecting the environment by controlling landfilled MSWI fly ash. CRediT authorship contribution statement Atsushi Ohbuchi: Writing - original draft, Writing - review & editing, Data curation. Kengo Fujii: Formal analysis. Miki Kasari: Formal analysis. Yuya Koike: Conceptualization, Supervision, Writing - review & editing. Acknowledgments The authors would like to thank Dr. Kiyoshi Nomura, Meiji University, for their continuing guidance and encouragement throughout this work. Appendix A. Supplementary data Supplementary data to this article can be found online at https://doi.org/10.1016/j.chemosphere.2020.126007. References Abollino, O., Aceto, M., Malandrino, M., Mentasti, E., Sarzanini, C., Petrella, F., 2002. Heavy metals in agricultural soils from Piedmont, Italy, Distribution, speciation and chemometric data treatment. Chemosphere 49, 545e557. https://doi.org/ 10.1016/S0045-6535(02)00352-1. Aubert, J.E., Husson, B., Sarramone, N., 2006. Utilization of municipal solid waste incineration (MSWI) fly ash in blended cement Part1: processing and characterization of MSWI fly ash. J. Hazard Mater. B136, 624e631. https://doi.org/ 10.1016/j.jhazmat.2005.12.041. Bogush, A., Stegemann, J., Wood, I., Roy, A., 2015. Element composition and mineralogical characterisation of air pollution control residue from UK energyfrom-waste facilities. Waste Manag. 36, 119e129. https://doi.org/10.1016/ j.wasman.2014.11.017. Chen, Z., Lu, S., Mao, Q., Buekens, A., Chang, W., Wang, X., Yan, J., 2016. Suppressing heavy metal leaching through ball milling of fly ash. Energies 9, 524e536. https://doi.org/10.3390/en9070524. Fan, Y., Zhang, F.S., Zhu, J., Liu, Z., 2008. Effective utilization of waste ash from MSW and coal co-combustion power plant-Zeolite synthesis. J. Hazard Mater. 153,
382e388. https://doi.org/10.1016/j.jhazmat.2007.08.061. Fujii, K., Ochi, K., Ohbuchi, A., Koike, Y., 2018. Evaluation of physicochemical properties of radioactive cesium in municipal solid waste incineration fly ash by particle size classification and leaching tests. J. Environ. Manag. 217, 157e163. https://doi.org/10.1016/j.jenvman.2018.03.028. Funari, V., Mantovani, L., Vigloitti, L., Tribaudino, M., Dinelli, E., Braga, R., 2018. Superparamagnetic iron oxides nanoparticles from municipal solid waste incinerators. Sci. Total Environ. 36, 119e129. https://doi.org/10.1016/ j.scitotenv.2017.11.289. Guirado, F., Gali, S., Chinchon, S., 2000. Quantitative Rietveld analysis of aluminous cement clinker phases. Cement Concr. Res. 30, 1023e1029. https://doi.org/ 10.1016/S0008-8846(00)00289-1. Harada, H., Yamamoto, T., Takaoka, M., 2011. Relation between chemical state and leaching property of lead in fly ash treated by mechanochemical method (in Japanese). Spring-8 Res. Rep. 1, 31e33. https://doi.org/10.18957/rr.1.2.31. Iwahana, Y., Ohbuchi, A., Koike, Y., Kitano, M., Nakamura, T., 2013. Radioactive nuclides in the incinerator ashes of municipal solid wastes before and after the accident at the Fukushima nuclear power plant. Anal. Sci. 29, 61e66. https:// doi.org/10.2116/analsci.29.61. Iwahana, Y., Ohbuchi, A., Koike, Y., Kitano, M., Nakamura, T., 2017. Speciation of the radioactive nuclides in incinerator fly ash of municipal solid waste using sequential extractions. J. Mater. Cycles Waste Manag. 19, 226e234. https:// doi.org/10.1007/s10163-015-0408-5. Koike, Y., Suzuki, R., Ochi, K., Hagiwara, K., Nakamura, T., 2017. Radioactivity analysis using commercially available chemical reagents as calibration sources. Bunseki Kagaku 66, 263e270. https://doi.org/10.2116/bunsekikagaku.66.263 (in Japanese). Komori, M., Shozugawa, K., Nogawa, N., Matsuo, M., 2013. Evaluation of radioactive contamination caused by each plant Fukushima Daiichi Nuclear Power Station using 134Cs/137Cs activity ratio as an index. Bunseki Kagaku 62, 475e483. https://doi.org/10.2116/bunsekikagaku.62.475 (in Japanese). Ministry of Environment, 2011. accessed. https://www.env.go.jp/jishin/attach/ waste-radioCs-16pref-result20110829.pdf. (Accessed 29 April 2017). Ministry of the Environment Government of Japan, 2015. Management and Treatment of Decontamination Wastes. FY2014 Decontamination Report, pp. 161e178. Nishida, K., Nagayoshi, Y., Ota, H., Nagasawa, H., 2001. Melting and stone production using MSW incinerated ash. Waste Manag. 21, 443e449. https://doi.org/ 10.1016/S0956-053X(00)00136-7. Ochi, K., Fujii, K., Hagiwara, K., Ohbuchi, A., Koike, Y., 2017. Characterization of radiocesium in soils sampled at the Koshinetsu and Kanto region. Bunseki Kagaku 66, 175e180. https://doi.org/10.2116/bunsekikagaku.66.175 (in Japanese). Ohbuchi, A., Ochi, K., Koike, Y., Nomura, K., Konya, T., Yamada, Y., Fujinawa, G., Nakamura, T., 2016. Composition and radio-cesium analysis of fly ash exhausted from incinerated general municipal waste in Fukushima prefecture. Adv. X-ray. Chem. Anal., Japan 47, 225e232 (in Japanese). Ohbuchi, A., Koike, Y., Nakamura, T., 2019. Quantitative phase analysis of fly ash of municipal solid waste by X-ray powder diffractometry/Rietveld refinement. J. Mater. Cycles Waste Manag. 21, 829e837. https://doi.org/10.1007/s10163-01900838-0. Okada, T., Matsuto, T., 2009. Determination of lead speciation in melting furnace fly ash by sequential chemical extraction. Chemosphere 75, 272e277. https:// doi.org/10.1016/j.chemosphere.2008.11.071. O’Connor, B.H., Raven, M.D., 1988. Application of the Rietveld refinement procedure in assaying powdered mixtures. Powder Diffr. 3, 2e6. https://doi.org/10.1017/ S0885715600013026. Pariatamby, A., Subramaniam, C., Mizutani, S., Takatsuki, H., 2006. Solidification and stabilization of fly ash from mixed hazardous waste incinerator using ordinary Portland cement. Environ. Sci. 13, 289e296. Qian, G., Song, Y., Zhang, C., Xia, Y., Zhang, H., Chui, P., 2006. Diopside-based glassceramics MSW fly ash and bottom ash. Waste Manag. 26, 1462e1467. https:// doi.org/10.1016/j.wasman.2005.12.009. , H., Corsaro, A., Hartmann-Koval, S., Juchelkov Raclavska a, D., 2017. Enrichment and distribution of 24 elements within the sub-sieve particle size distribution ranges of fly ash from wastes incinerator plants. J. Environ. Manag. 203, 1169e1177. https://doi.org/10.1016/j.jenvman.2017.03.073. Rietveld, H.M., 1969. A profile refinement method for nuclear and magnetic structures. J. Appl. Crystallogr. 2, 65e71. https://doi.org/10.1107/ S0021889869006558. Rosado, D., Usero, J., Morillo, J., 2016. Ability of 3 extraction methods (BCR, Tessier and protease K) to estimate bioavailable metals in sediments from Huelva estuary (Southwestern Spain). Mar. Pollut. Bull. 102, 65e71. https://doi.org/ 10.1016/j.marpolbul.2015.11.057. Saffarzadeh, A., Shimaoka, T., Kakuta, Y., Kawano, T., 2014. Cesium distribution and phases in proxy experiments on the incineration of radioactively contaminated waste from the Fukushima area. J. Environ. Radioact. 136, 76e84. https:// doi.org/10.1016/j.jenvrad.2014.05.009. Saikia, N., Kato, S., Kojima, T., 2007. Production of cement clinkers from municipal solid waste incineration (MSWI) fly ash. Waste Manag. 27, 1178e1189. https:// doi.org/10.1016/j.wasman.2006.06.004. Sakai, S., Mizutani, S., Takatsuki, H., Kishida, T., 1995. Leaching test of metallic compounds in fly ash of solid waste incinerator. J. Mater. Cycles Waste Manag. 6, 225e234. https://doi.org/10.3985/jswme.6.225 (in Japanese). Shiota, K., Takaoka, M., Fujimori, T., Oshita, K., Terada, Y., 2015. Cesium speciation in
A. Ohbuchi et al. / Chemosphere 248 (2020) 126007 dust from municipal solid waste and sewage sludge incineration by synchrotron radiation micro-x-ray analysis. Anal. Chem. 87, 11249e11254. https://doi.org/ 10.1021/acs.analchem.5b03298. Singh, G.V.P.B., Subramaniam, K.V.L., 2016. Quantitative XRD study of amorphous phase in alkali activated low calcium siliceous fly ash. Construct. Build. Mater. 124, 139e147. https://doi.org/10.1016/j.conbuildmat.2016.07.081. Steinhauser, G., Brandl, A., Johnson, T.E., 2014. Comparison of the Chernobyl and Fukushima nuclear accidents: a review of the environmental impacts. Sci. Total Environ. 470, 800e817. https://doi.org/10.1016/j.scitotenv.2013.10.029. Sukandar Padmi, T., Tanaka, M., Aoyama, I., 2009. Chemical stabilization of medical waste fly ash using chelating agent and phosphates: heavy metals and ecotoxicity evaluation. Waste Manag. 29, 2065e2070. https://doi.org/10.1016/ j.wasman.2009.03.005. Taylor, J.C., Hinczak, I., Matulis, C.E., 2000. Rietveld full-profile quantification of
9
portland cement clinker: the importance of including a full crystallography of the major phase polymorphs. Powder Diffr. 15, 7e18. https://doi.org/10.1017/ S0885715600010769. Tessier, A., Campbell, P.G.C., Bisson, M., 1979. Sequential extraction procedure for the speciation of particulate trace metals. Anal. Chem. 51, 844e851. https:// doi.org/10.1021/ac50043a017, 1979. Tojo, Y., Ishii, M., Matsuo, T., Shimaoka, T., 2014. Study on the existence form of hardly-soluble cesium contained in incineration bottom ash and its long-term stability. In: The Proceedings of the 25rd Annual Conference of Japan Society of Material Cycles and Waste Management. https://doi.org/10.14912/ jsmcwm.25.0_477. Toraya, H., 1990. Array-type universal profile function for powder pattern fitting. J. Appl. Crystallogr. 23, 485e491. https://doi.org/10.1107/S002188989000704X.
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Characterization of soluble and insoluble radioactive cesium in municipal solid waste incineration fly ash Atsushi Ohbuchi a, *, Kengo Fujii b, Miki Kasari b, Yuya Koike c a
Rigaku Americas Corporation, 9009 New Trails Drive, The Woodlands, Texas, 77381, USA Applied Chemistry Course, Graduate School of Science and Technology, Meiji University, 1-1-1 Higashimita, Tama-ku, Kawasaki, 214-8571, Japan c Department of Applied Chemistry, School of Science and Technology, Meiji University, 1-1-1 Higashimita, Tama-ku, Kawasaki, Kanagawa, 214-8571, Japan b
h i g h l i g h t s Radioactive Cs in MSWI fly ash was separated into soluble and insoluble forms. The result of Tessier method indicated that water-soluble radioactive Cs exists as CsCl. Insoluble radioactive Cs was trapped into silicate as amorphous phase result from chemical treatment. Silicate-bound and free radioactive Cs were contained into surface and inner part of the silicate amorphous phase.
a r t i c l e i n f o
a b s t r a c t
Article history: Received 11 October 2019 Received in revised form 18 January 2020 Accepted 21 January 2020 Available online 22 January 2020
Soluble and insoluble radioactive cesium in municipal solid waste incineration fly ash were analyzed by X-ray diffraction and gamma-ray spectrometry. A total of 60% of soluble radioactive cesium was determined using the Tessier extraction method, and it was almost same extraction rate with Japanese leaching test No.13. In addition, chloride compounds such as halite (NaCl) and sylvite (KCl) showed same behavior with soluble radioactive cesium, therefore, soluble radioactive cesium existed as a chloride (CsCl) with water solubility characteristics. Almost insoluble radioactive cesium trapped into silicate of crystalline phase or amorphous phase was eluted by hydrogen fluoride treatment. Radioactive 137Cs was released in three stages by heating treatment (untreated - 400 C, 600 Ce800 C, and 800 Ce1000 C) according to decreasing amorphous content. The relationship between the concentrations of radioactive 137 Cs and amorphous phase exhibited good linearity (R ¼ 0.9278). Insoluble radioactive 137Cs was contained in inner part of the amorphous phase, and free radioactive cesium was determined from the concentration of the amorphous phase. © 2020 Elsevier Ltd. All rights reserved.
Handling Editor: Martine Leermakers Keywords: Municipal solid waste incineration fly ash Soluble and insoluble radioactive cesium Tessier extraction method Chemical treatment Heating treatment
1. Introduction Considerable amounts of radioactive cesium having 11.8e18 PBq (134Cs) and 13e62.5 (137Cs) PBq (Steinhauser et al., 2014) were released into environment by the Fukushima Daiichi Nuclear Power Plant (FDNPP) accident. After the FDNPP accident, the concentration of radioactive cesium in soil near Kawasaki, located 300 km from the FDNPP, increased by a factor of ˃100 (Ochi et al., 2017). Moreover, the radioactive cesium concentration in waste collected at Kyusyu, located approximately 1200 km from FDNPP, was 5
* Corresponding author. Tel.: þ1 281 362 2300; fax: þ1 281 364 3628 E-mail addresses: [email protected], [email protected] (A. Ohbuchi). https://doi.org/10.1016/j.chemosphere.2020.126007 0045-6535/© 2020 Elsevier Ltd. All rights reserved.
times higher than the levels measured before the accident (Iwahana et al., 2013). Eight years after the FDNPP accident, radioactive cesium can be detected in high concentrations due to the long half-lives of 134Cs and 137Cs (T1/2 ¼ 2.06 and 30.07 years, respectively). The deposited radioactive cesium on the ground via dry and wet deposition were incinerated at an incineration plant to reduce the waste volume. After incineration, municipal solid waste incineration (MSWI) fly ash and bottom ash were produced, and both ashes were buried in landfills after stabilization treatment to prevent the elution of toxic components. The Ministry of the Environment Government of Japan has reported radioactive cesium in contaminated materials is contained in the fly and bottom ashes to fairly high concentrations, and a higher concentration of radioactive cesium in MSWI fly ash compared to that in MSWI bottom ash
2
A. Ohbuchi et al. / Chemosphere 248 (2020) 126007
(Ministry of the Ministry of Environment, 2011). The limit for radioactivity set by Japanese Ministry of the Environment is ˂8000 Bq kg1 in waste materials including fly ash. Radioactive waste is incinerated as usual waste material, and the generated ashes are subsequently stored in landfills. Waste materials with radioactivities of ˃8000 Bq kg1 are treated to control the radioactivity of the landfill site by enclosing around with soils of a water resistant layer to prevent contact with water, and putting an absorption layer of radioactive materials at underside (Ministry of the Ministry of the Environment Government of Japan, 2015). In contrast, fly ash with ˂8000 Bq kg1 can be recycled for uses in cement (Aubert et al., 2006; Saikia et al., 2007), ceramics (Qian et al., 2006), stone (Nishida et al., 2001), and zeolite (Fan et al., 2008), similar to regular MSWI fly ash. The physicochemical properties of fly ash were investigated by conducting leaching tests of heavy metals (Harada et al., 2011; Okada and Matsuto, 2009). Lead in fly ash was specified by sequential chemical extraction (Sukandar et al., 2009), leaching of Cu, Cr, and Pb were suppressed by ball milling (Chen et al., 2016). Moreover, enrichment and distribution of heavy metals were et al., 2017). However, the physicochemical investigated (Raclavska properties of radioactive nuclides are required for further comprehensive understanding of fly ash characteristics. Studies regarding the speciation analyses of radioactive cesium in fly ash have been reported after the FDNPP accident (Saffarzadeh et al., 2014; Tojo et al., 2014; Shiota et al., 2015; Iwahana et al., 2017). Iwahana (Iwahana et al., 2017) and co-workers reported the chemical speciation of 210Pb using the sequential extraction method proposed by Tessier (Tessier et al., 1979), and the chemical form differed from that of stable Pb. An insoluble radioactive cesium in bottom ash was contained to the amorphous matter (Tojo et al., 2014). The chemical form of radioactive cesium could be separated into water-soluble and insoluble forms using the Japanese leaching test No. 13 (JLT-13) defined by the Ministry of the Environment Government of Japan. The JLT-13 can be applied to MSWI fly ash to determine the leaching properties of metals (Sakai et al., 1995; Pariatamby et al., 2006). The physicochemical properties of radioactive cesium in fly ash were also studied using the JLT13 (Ohbuchi et al., 2016; Fujii et al., 2018). Approximately 60% of radioactive cesium was present as water-soluble forms in fly ash (Ohbuchi et al., 2016). Moreover, the elution ratio of radioactive cesium from fly ash increased with decrease in the particle size and was influenced by the presence of chloride compounds such as sodium chloride (NaCl) and potassium chloride (KCl). Therefore, radioactive cesium in fly ash is likely contained as chloride compounds such as CsCl (Fujii et al., 2018). Estimation of the chemical forms of radioactive cesium in fly ash is useful for the safe recycling and control of landfilled fly ash. Herein, characteristic of radioactive cesium in MSWI fly ash contaminated by the FDNPP accident was evaluated. Especially, estimation of the chemical form of insoluble radioactive cesium in the amorphous phase was performed, including quantitative analysis of the amorphous phase by Rietveld refinement (Rietveld, 1969) which was applied to various materials such as cement (Guirado et al., 2000; Taylor et al., 2000), and waste materials (Singh and Subramaniam, 2016; Ohbuchi et al., 2019). The sequential extraction method developed by Tessier was used to further evaluate the form of soluble radioactive cesium. Moreover, the chemical speciation of insoluble radioactive cesium was evaluated considering the relationship between the concentrations of radioactive cesium and amorphous phase by chemical and heat treatments.
2. Materials and methods 2.1. Sample preparation MSWI fly ash samples, which was same sample with previous study (Ohbuchi et al., 2016), were collected from a municipal waste incineration plant in Fukushima Prefecture, Japan, on January 2013 and dried at 105 C for 24 h. The combustion capacity of plant is 300-ton day1 with two stoker furnaces in the plant at temperature between 800 and 1000 C where municipal solid waste (MSW) of general component is combusted. The bottom ash was composed of cinder cooled with water. The fly ash was collected from an electrostatic precipitator after spraying with slaked lime to neutralize acid gases. About one kg of fly ash was fractionated to 20 g by conical quartering. The activity ratio of radioactive nuclides 134 Cs/137Cs in MSWI fly ash derived from the FDNPP accident was previously determined to be 1:1 (Komori et al., 2013) and the behavior of 134Cs is similar to that of 137Cs (Saffarzadeh et al., 2014). The activity ratio of 134Cs/137Cs in all samples was decay-corrected on March 11, 2011, the day of the FDNPP accident. Gamma-ray spectrometry indicated that the radioactive cesium in the fly ash originated from the FDNPP accident. 2.2. Gamma-ray spectrometry The activity of radioactive cesium was determined via gammaray spectrometry using a p-type high-purity Ge/coaxial-type semiconductor detector (HPGe; IGC 10200, Princeton Gamma Tech Instruments, Inc., USA) surrounded by a 100 mm-thick lead shield with 50 mm-thick oxygen-free copper and 5 mm-thick acrylic plates. Each of the classified fly ash samples was compressed in the U8 container (height and diameter of 68 and 56 mm, respectively, Sekiya Rika Co. Ltd, Japan). Detection efficiencies were calculated for gamma ray spectrum of a152Eu standard source (diameter and height of 25 and 6.0 mm, respectively, Japan Radioisotope Association, Japan). The detection efficiency curve drawn using detection efficiencies of standard source was corrected using the 1461 keV gamma-ray activity emitted from 4 K in KCl (Koike et al., 2017; Fujii et al., 2018). Koike et al. (2017) have developed a gamma-ray spectrometry calibration method using natural radionuclides included in commercially available chemical regents at a noncontrolled area in Japan. The activities of 134Cs and 137Cs were determined by the emitted gamma rays, i.e., 606 and 662 keV, respectively. 2.3. X-ray diffractometry A SmartLab diffractometer (Rigaku, Japan) equipped with a horizontal goniometer in Bragg-Brentano para-focusing geometry and CuKa1,2 (2 kW X-ray tube) with a one-dimensional silicon strip detector D/teX Ultra250 were used for crystalline phase analysis. The samples were loaded into a glass sample holder by samplefront-pressing. The diffraction patterns of the samples were recorded from 5 to 80 /2q at 0.01 intervals and at a 2 /min scanning speed. Phase identification and quantitative analysis by Rietveld refinement were performed using the integrated X-ray powder diffraction software PDXL (Rigaku, Japan). 2.4. X-ray fluorescence spectrometry The major and minor elements in fly ash were analyzed using a Rigaku ZSX Primus IV (Rigaku, Japan) X-ray fluorescence spectrometer equipped with an end window containing a 4 kW Rh Xray tube. The analyzer crystals were LiF(200), Ge(111), PET(002), and RX25. A NaI scintillation counter and proportional counter with
A. Ohbuchi et al. / Chemosphere 248 (2020) 126007
flowing P-10 gas composed of Ar (90%) and CH4 (10%) were used as detectors. The gas flow rate of the P-10 gas was 50 cm3 min1. 2.5. Rietveld refinement
3
(i) Ion exchangeable fraction Five g of fly ash was leached for 1 h at 25 C with continuous agitation using 40 mL of 1 mol L1 magnesium chloride (MgCl2, Junsei Chemical Co. ltd, Japan).
Pattern fitting was performed using PDXL software and was based on Rietveld method. Rietveld refinement was applied over the entire diffraction profile (for example 5e90 /2q). The background for each pattern was defined as the interpolation of n points that were manually introduced. The profile function used a split pseudo-Voigt function (Toraya, 1990) to consider the asymmetry of each peak. The optimized parameters were: background coefficients, peak shift, lattice constant, full width at half maximum (FWHM), and peak shape. The quantitative values of each crystalline phase were calculated as follows:
Forty mL of 1 mol L1 sodium acetic acid buffer (pH 5) prepared using sodium acetate (CH3COONa, Junsei Chemical Co. ltd, Japan), acetate acid (CH3COOH, Junsei Chemical Co. ltd, Japan), and distillated water was added to the residues from step (i) for 6 h at room temperature to leach carbonate bound materials.
ðS Z M V Þ W i ¼ P i i i i j Sj Zj Mj Vj
The free oxide phases were extracted using 100 mL of 0.04 mol L1 of hydroxylamine hydrochloride (NH2OH HCl, Wako Pure Chemical Co., Japan) heated at 96 C for 6 h.
(1)
In Eq. (1), Wi is the weight fraction of the analyte crystal i, S is the scale factor after the Rietveld refinement, Z is the number of molecules in a unit cell, M is the molecular weight, and V is the unit cell volume derived from the lattice constant. The concentration of amorphous phase was calculated using the following equations via the external standard method (O’Connor and Raven, 1988) using corundum (a-Al2O3: Kojyundo Chemical Laboratory Co. Ltd, Japan):
G ¼ SCor
rCor V 2Cor m*Cor CCor
(2)
In Eq. (2), SCor is the Rietveld scale factor for corundum, rCor is the corundum density, VCor is the corundum unit-cell volume, CCor is the corundum weight fraction (100 mass%), and m*Cor is the corundum mass absorption coefficient. The G factor was obtained using a pure standard material with high crystallinity. The concentration of the crystalline phase i was calculated using the following equation by substitution of the G factor.
C i ¼ Si
ri V 2i m*sample G
100
X
Ci
(iii) Free oxide fraction
(iv) Bound to organic matter fraction The residue of step (iii) was agitated in 25 mL of hydrogen peroxide (H2O2, Junsei Chemical Co. ltd, Japan) and 15 mL of 0.02 mol L1 nitric acid at 85 C for 3 h. After treatment, 25 mL of 3.2 mol L1 ammonium acetate (CH3COONH4, Wako Pure Chemical Co.), 20 mL of distillated water, and 15 mL of 0.02 mol L1 nitric acid were added and stirred to extract organic and sulfide matter for 3 h at 25 C. (v) Residue fraction The solid material remaining after step (iv) was referred to as the residual materials. The raw fly ash and four residues from extraction steps (i)e(iv) were analyzed by powder XRD to determine the speciation of the crystalline and amorphous phases, and gamma-ray spectrometry was performed for analysis of radioactive nuclides. 2.7. Chemical treatment
(3)
In Eq. (3), Ci is concentration of the crystalline phase i, Si is the Rietveld scale factor of the crystalline phase i, ri is the crystalline phase i density, Vi is unit-cell volume of the crystalline phase i, and m*sample is the mass absorption coefficient of the sample. The m*sample value was calculated from elemental analysis by X-ray fluorescence spectrometry. The concentration of amorphous phase CAmo is calculated by the following equation (4).
CAmo ¼ 100
(ii) Carbonate bound fraction
(4)
2.6. Sequential extraction via the tessier extraction method The sequential extraction via the Tessier extraction method was used to determine the speciation of the radioactive nuclides in MSWI fly ash. This method is often used to determine the speciation of heavy metals in soil and sediment samples (Abollino et al., 2002; Rosado et al., 2016) and the fractions can be classified into five phases; ion exchangeable (IE), carbonate bound (CB), FeeMn oxide (OX), bound to organic matter (OB), and residual (Res) fractions using the appropriate extraction reagents. The extraction method used herein included the following steps.
The JLT-13 specifies that a mixture (S/L ¼ 0.1) of 50 mL of pure water (pH ¼ 6.20) and MSWI fly ash dried by 105 C for 24 h should be subjected to continuous shaking for 6 h at 25 C. A mechanical shaker (Shaking Bath TBK 602DA, Advantec Inc., Japan) was used to prepare the eluted solutions from fly ash. The shaker velocity was approximately 200 rpm. After shaking, the eluted solutions were separated using filter paper (Whatman™ glass microfiber filters, 100 circles, GE Healthcare Life Science, USA). Each chemical treatment for dissolving the insoluble radioactive cesium in amorphous phase of MSWI fly ash was carried out as the following procedures. MSWI fly ash after the JLT-13 treatment was used for each chemical treatment. (a): Nitrohydrochloric acid derived from nitric acid (HNO3, Junsei Chemical Co. ltd, Japan) and hydrochloric acid (HCl, Junsei Chemical Co. ltd, Japan). Twenty mL of nitrohydrochloric acid of pH 1e5 used for evaluation in acid region was added to 1 g of MSWI fly ash, and the mixture was heated at 100 C for 6 h. (b): Sodium hydroxide (NaOH, Wako Pure Chemical Co., Japan). Twenty mL of sodium hydroxide solution was added to 1 g of MSWI fly ash, and the mixture was stirred for 6 h. (c): Hydrogen fluoride (HF, Wako Pure Chemical Co., Japan). Eighty mL of nitric acid and 20 mL of hydrogen fluoride were added to 5 g of MSWI fly ash, and the mixture was heated at 95 C
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for 6 h. Each eluted solution was separated using a filter paper, and then filtered solutions were separated to obtain residues and elutions via centrifugation at 3000 rpm for 20 min. Each eluted solution was heated immediately to evaporate the solvent for dryness. All ashes were ground by a hi-speed vibrating sample mill (TI-100, CMT Co., Ltd., Japan) before measurement. 2.8. Heat treatment MSWI fly ashes after the JLT-13 were heated using a muffle furnace (KDF S-70, Denken-Highdental Co., Ltd., Japan) at 400, 600, 800 and 1000 C for 24 h to release insoluble radioactive cesium in amorphous phase by crystallization. 3. Results and discussion 3.1. Crystal morphology in sequentially extracted MSWI fly ash XRD analysis was conducted to investigate the matrix and crystalline phase of the MSWI fly ash since crystalline in the MSWI fly ash and varied by waste composition and incineration conditions used in the incineration facility. Also, speciation of soluble radioactive cesium was estimated as chloride compound by crystalline components in MSWI fly ash (Fujii et al., 2018). Therefore, crystalline phases contained in MSWI fly ash were investigated via XRD combined with the sequential extraction method. The X-ray diffraction patterns of each residue including raw MSWI fly ash are shown in Fig. 1. Anhydrite (CaSO4), biotite (KFeMg2Al3O10(H2O)2), calcium aluminum oxide (Ca3Al2O6), calcite (CaCO3), calcium chloride hydroxide (CaClOH), cordierite (Mg2Al4Si5O18), gehlenite (Ca2Al2SiO7), halite (NaCl), larnite (Ca2SiO4), portlandite (Ca(OH)2), quartz (SiO2), and sylvite (KCl) were identified from the diffraction pattern of raw MSWI fly ash. The crystalline phases differed compared to other MSWI fly ashes (Bogush et al., 2015; Funari et al., 2018; Ohbuchi et al., 2019). It is considered that components in MSWI fly ash were depending on MSW at
Fig. 1. X-ray diffraction patterns of raw MSWI fly ash and each extracted residue.(a) Raw MSWI fly ash, (b) IE fraction, (c) CB fraction, (d) OX fraction, and (e) bound to organic matter fraction residues. Alb: albite (NaAlSi3O8), Anh: anhydride (CaSO4), Bas: bassanite (CaSO4(H2O)0.5), Bio: biotite (KFeMg2(AlSi3O10(OH)2)), Cal: calcite (CaCO3), Cao: calcium aluminum oxide (Ca3Al2O6), Cch: calcium chloride hydroxide (CaClOH), Cor: cordierite (Mg2Al4Si5O18), Cri: cristobalite (SiO2), Etr: ettringite (Ca6(Al(OH)6)2(SO4)3(H2O)25.7), Geh: gehlenite (Ca2Al2SiO7), Hal: halite (NaCl), Hem: Hematite (Fe2O3), Lar: larnite (Ca2SiO4), Mag: magnetite (MgCO3), Ort: orthoclase (KAlSi3O8), Por: portlandite (Ca(OH)2), Qtz: quartz (SiO2), Rut: rutile (TiO2), Syl: sylvite (KCl), and Tob: tobermorite (Ca2.25Si3O5(OH)2(H2O)).
each region even if general municipal solid wastes (MSWs) were incinerated. Quartz is a major soil component, anhydride is a reaction product of SO2 and slaked lime in air, and calcite is a product of CO2 and slaked lime. Calcium chloride hydroxide, halite, and sylvite as chloride-containing compounds were likely derived from kitchen wastes including vegetables, seasonings, and plastics. Gehlenite and larnite are formed via crystallization of aluminosilicate by incinerating MSWs. After IE extraction, the diffraction peaks of the three chloride-containing compounds disappeared due to dissolution. Previously, chloride-containing compounds were dissolved in the JLT-13 using distillated water same with the IE fraction residue (Ohbuchi et al., 2016). In other words, IE and water extraction are considered to be similar extraction processes for chloride compounds such as halite, and sylvite in MSWI fly ash. After the sequential extraction, oxide compounds were identified in the diffraction pattern of the residue bound to the organic matter. The identified crystalline and amorphous phases in each residue and raw MSWI fly ash were calculated via Rietveld refinement combined with the external standard method (O’Connor and Raven, 1988). Table 1 shows the quantification results of the crystalline and amorphous phases. The amorphous phase concentration in MSWI fly ash was calculated to be approximately 30 mass%, and the amorphous phase concentration in each extraction residue increased relatively compared to that in the raw MSWI fly ash, reaching approximately 86 mass% in the final residue. The relationship between the amorphous phase and radioactive cesium is discussed in the next section in the context of evaluating the soluble and insoluble radioactive cesium. 3.2. Estimation of radioactive cesium crystal morphology The radioactivity concentration in raw MSWI fly ash was calculated by gamma-ray spectrometry. A radioactivity of approximately 5800 Bq kg1 was calculated as the total concentration of 134 Cs and 137Cs (Ohbuchi et al., 2016), which was below the regulation limit for landfilled wastes. However, investigating crystal morphologies of radioactive cesium are needed for a comprehensive understanding of the contaminated MSWI fly ash for recycling or landfilling even if radioactivity was below the regulation limit for landfilled wastes. In our previous research, soluble radioactive cesium was contained as chloride compound in MSWI fly ash, on the other hand, other crystal morphologies of radioactive cesium were not estimated. Therefore, crystal morphology of radioactive cesium was investigated by Tessier extraction method. The elution rate of radioactive cesium from MSWI fly ash at each fraction by the Tessier method is shown in Fig. 2. Similar elution behaviors were observed for radioactive 134Cs and 137Cs during each extraction process. Halite and sylvite of alkali metal chloride were dissolved during extraction of the IE fraction residue (Fig. 1), and 60% elution rate of radioactive cesium obtained by the IE fraction extraction was similar to that obtained using distilled water following the JLT-13 method (Fujii et al., 2018). It is considered that radioactive cesium dissolved by IE fraction was contained as chloride morphology (CsCl) having water-soluble characteristics in MSWI fly ash. In other words, almost same compounds were dissolved by distilled water used by the JLT-13 or magnesium chloride treatment used by IE fraction. The elution rates of radioactive cesium in the IE fraction were the highest at approximately 60% from the raw fly ash, whereas the elution rates in other fractions were ˂10% except for the CB fraction. Radioactive cesium in MSWI fly ash was separated into two crystal forms, namely, watersoluble or insoluble forms although water-soluble radioactive cesium was primarily contained as CsCl. For comprehending of insoluble radioactive cesium, relationship between elution rates of radioactive cesium and amorphous content was confirmed. Fig. 3
A. Ohbuchi et al. / Chemosphere 248 (2020) 126007
5
Table 1 Concentrations of crystalline and amorphous phases in raw MSWI fly ash and each extraction fraction as determined by Tessier method. Crystalline phase
Concentration/mass%
Raw fly ash Anhydrite (CaSO4) Biotite (KFeMg2(AlSi3O10(OH)2) Calcium aluminum oxide (Ca3Al2O6) Calcium chloride hydroxide (CaClOH) Calcite (CaCO3) Cordierite (Mg2Al4Si5O18) Gehlenite (Ca2Al2SiO7) Halite (NaCl) Larnite (Ca2SiO4) Portlandite (Ca(OH)2) Quartz (SiO2) Sylvite (KCl) Amorphous
2.6 0.7 1.1 15.3 8.4 4.2 7.1 7.6 3.4 14.2 0.3 4.5 30.8
Residue of the CB fraction Bassanite (CaSO4(H2O)0.5) Brucite (Mg(OH)2) Calcite (CaCO3) Cordierite (Mg2Al4Si5O18) Gehlenite (Ca2Al2SiO7) Hematite (Fe2O3) Orthoclase (KAlSi3O8) Quartz (SiO2) Tobermorite ((CaO)5(SiO2)(H2O)5) Amorphous
3.2 12.9 14.2 1.1 13.2 0.7 1.7 1.9 0.9 49.1
Residue of the bound to organic matter fraction Albite (NaAlSi3O8) Cristobalite (SiO2) Hematite (Fe2O3) Magnetite (Fe3O4) Orthoclase (KAlSi3O8) Periclase (MgO) Quartz (SiO2) Rutile (TiO2) Amorphous
3.3 0.4 3.9 0.4 0.8 0.2 4.5 0.9 85.8
Crystalline phase
Concentration/mass%
Residue of the IE fraction Bassanite (CaSO4(H2O)0.5) Brucite (Mg(OH)2) Calcite (CaCO3) Gehlenite (Ca2Al2SiO7) Hematite (Fe2O3) Orthoclase (KAlSi3O8) Quartz (SiO2) Amorphous
2.1 10.4 10.3 5.7 0.8 0.8 2.1 67.8
Residue of the free OX fraction Albite (NaAlSi3O8) Cristobalite (SiO2) Ettringite (Ca6(Al(OH)6)2(SO4)3(H2O)26) Hematite (Fe2O3) Magnetite (Fe3O4) Orthoclase (KAlSi3O8) Periclase (MgO) Quartz (SiO2) Rutile (TiO2) Amorphous
1.1 1.0 0.5 4.3 0.7 0.6 0.7 4.3 1.0 86.1
radioactive cesium was decreased gradually since almost soluble radioactive cesium was dissolved by IE fraction. Therefore, the relationship between the elution rate of the soluble radioactive cesium and the amorphous content was shown as negative correlation. In the final residue, almost all insoluble radioactive cesium was contained among total radioactive cesium. Hence, the existence form of insoluble cesium in MSWI fly ash was considered to be trapped in the amorphous phase or combined with silicate. To evaluate the radioactive cesium trapped in the amorphous phase, chemical and heat treatments were applied.
3.3. Amorphous phase composition determination with the trapped insoluble radioactive cesium using chemical treatment
Fig. 2. Elution rate of radioactive cesium determined by the Tessier method. IE: Ion exchangeable fraction, CB: Carbonate bound fraction, OX: Free oxide fraction, OB: Bound to organic matter fraction, Res: Residue fraction.
shows the relationship of 134Cs and 137Cs in terms of their elution rates and amorphous content (good linearity; R ¼ 0.8). The amorphous content in raw MSWI fly ash was approximately 30 mass%, and the amorphous content increased to approximately 86 mass% relatively by extracting the soluble crystalline phases and radioactive cesium. On the other hand, the elution rate of the soluble
Insoluble radioactive cesium was considered to be primarily contained in the amorphous phase, although composition of amorphous phase was initially unknown. The amorphous phase composition with the trapped radioactive cesium was confirmed by chemical treatments. MSWI fly ash after the JLT-13 treatment to remove water-soluble radioactive cesium was chemically treated with hydrogen fluoride, nitrohydrochloric acid, and sodium hydroxide. Table 2 shows the elution rates of insoluble radioactive 137Cs from MSWI fly ash and the amorphous content in the residue with various chemical treatments. Insoluble radioactive 137Cs was confirmed because the 134 Cs content was excessively low. The elution rate of insoluble radioactive cesium by hydrogen fluoride treatment was shown largest value compared to the other chemical treatments. Table 3 lists the elemental compositions of the residues obtained after
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Fig. 3. Relationship between the elution rate of radioactive cesium and amorphous phase content.
Table 2 Elution rate of insoluble radioactive
137
Cs and amorphous phase after various chemical treatments.
Chemical treatment
Elution rate of the insoluble radioactive
JLT-13 Hydrogen fluoride Nitrohydrochloric acid (pH ¼ 1) Nitrohydrochloric acid (pH ¼ 3) Nitrohydrochloric acid (pH ¼ 5) NaOH (pH ¼ 10)
e 93.3 17.8 15.2 7.0 4.9
137
Cs/%
Amorphous phase content/mass% 67.1 39.4 26.6 21.3 21.3 27.4
Table 3 Elemental composition of MSWI fly ash residues after various chemical treatments. Element
Na2O MgO Al2O3 SiO2 P2O5 SO3 K2O CaO TiO2 Fe2O3
Concentration/mass% Hydrogen fluoride
Nitrohydrochloric acid (pH 1)
Nitrohydrochloric acid (pH 3)
Nitrohydrochloric acid (pH 5)
NaOH (pH 10)
1.4 2.3 12.1 3.2 0.1 0.6 0.1 76.1 1.1 2.5
1.3 2.1 9.4 18.0 1.4 2.5 0.3 58.1 2.1 1.6
1.3 1.9 7.7 15.8 1.2 3.9 0.3 61.8 1.9 2.0
0.5 1.7 7.6 15.5 1.2 4.0 0.3 63.0 1.9 2.0
1.0 1.9 7.9 15.8 1.2 4.4 0.3 61.6 1.9 1.9
each chemical treatment and Fig. 4 shows identification of crystalline phases in each residue. The SiO2 concentration after hydrogen fluoride treatment was shown lowest value, in contrast, it was maintained at approximately 15 mass% after the other chemical treatments. Also, diffraction peaks of quartz were disappeared and silicon was identified on the diffraction pattern of hydrogen fluoride treatment although diffraction peaks of quartz were observed on diffraction patterns of other chemical treatment residues. It is considered that silicates in amorphous phase and SiO2 of crystalline phase were dissolved only via hydrogen fluoride treatment, as a result, insoluble radioactive cesium contained into silicate phases was released. The elution rate obtained using nitrohydrochloric acid at each pH and sodium hydroxide treatments were lower than that obtained using hydrogen fluoride treatment although the amorphous phase contents decreased. The amorphous phases with other compositions such as Al2O3 and CaO differed from silicates were dissolved by nitrohydrochloric acid and sodium hydroxide treatments, although they did not almost
contain insoluble radioactive cesium, unlike the silicate amorphous phase. Therefore, the most of insoluble radioactive cesium was determined to be trapped in silicates of crystal or amorphous phases. 3.4. Heat treatment to release insoluble radioactive cesium from the amorphous phase A common approach for evaluating insoluble radioactive cesium involves crystallization of the amorphous phase by heating and determining the relationship between concentrations of radioactive cesium and amorphous phase. Water-soluble radioactive cesium in MSWI fly ash was extracted according to the JLT-13 protocol several times to evaluate only the insoluble radioactive cesium. The associated extraction residues were heated using an electric furnace at 400, 600, 800, and 1000 C. After each heating process, the concentration of radioactive cesium and amorphous phase were determined. Table 4 shows the
A. Ohbuchi et al. / Chemosphere 248 (2020) 126007
Fig. 4. X-ray diffraction patterns of MSWI fly ash after JLT-13 (a) treated by (b) hydrogen fluoride, (c) nitrohydrochloride acid (pH ¼ 1), (d) nitrohydrochloride acid (pH ¼ 3), (e) nitrohydrochloride acid (pH ¼ 5), and (f) NaOH. And: andradite (Ca3Fe2(SiO4)O3), Anh: Anhydrite (CaSO4), Cal: calcite (CaCO3), Cao: calcium aluminum oxide (Ca3Al2O6), Cch; calcium chloride hydroxide (CaClOH), Geh: gehlenite (Ca2Al2SiO7), Chi: chiolite (Na5Al3F14), Cli: clinotobemorite (Ca5Si6O17(H2O)5), Hat: hatrurite (Ca3SiO5), Hem: hematite (Fe2O3), Heu: Heulandite-Ca (Ca2Al4Si14O36(H2O)12), Hyd: hydrocalumite (Ca2Al(CO3)0.25Cl0.5(OH)6(H2O)2.4), Kya: kyanite (Al2SiO5), Lar: larnite (Ca2SiO4), Ort: orthoclase (KAlSi3O8), Por: portlandite (Ca(OH)2), Qrz: quartz (a-SiO2), Rut: rutile (TiO2), Sil: silicon (Si), Tri: tridymite (SiO2).
analytical results regarding the concentration rate of insoluble radioactive 137Cs and amorphous phase. The amorphous phase content decreased gradually by heating and after 400 C heating, the amorphous phase and 137Cs contents decreased in same manner. The amorphous phase content in MSWI fly ash heated at 1000 C was 4.7 mass%, whereas that of unheated MSWI fly ash was 67.1 mass%. The amorphous phase was crystallized upon heat treatment, decreasing its concentration. Moreover, radioactive 137 Cs content was 24.8% after heat treatment at 1000 C. The decreased concentration of radioactive 137Cs was observed in three stages (untreated to 400 C, 600e800 C, and 800e1000 C), where the radioactive 137Cs content remained nearly constant between 400 and 600 C. Fig. 5 shows the X-ray diffraction pattern at each heat treatment temperature. Similar X-ray diffraction patterns were observed until heating at 600 C, however, the amorphous phase content decreased at 400 C heating along with that of radioactive 137Cs. Therefore, some radioactive 137Cs was trapped in the amorphous phase crystallized at low temperatures and the surface of the silicate amorphous phase can be crystallized by low temperature heating. After the 800 C heat treatment, the concentration of insoluble radioactive 137Cs decreased remarkably although the amorphous concentration showed almost the same value with 600 C heat treatment. Therefore, the decreased insoluble radioactive 137Cs content after 800 C heating was due to decreases in the free-radioactive cesium contained in amorphous released by 600 C heating boiling point of Cs is approximately 670 C). After the 1000 C heat treatment, a different X-ray
Table 4 Concentration rate of insoluble radioactive
7
Fig. 5. X-ray diffraction patterns of MSWI fly ash after JLT-13 heated at (a) unheated, (b) 400 C, (c) 600 C, (d) 800 C, and (e) 1000 C. And: andradite (Ca3Fe2(SiO4)O3), Anh: Anhydrite (CaSO4), Cal: calcite (CaCO3), Cao: calcium aluminum oxide (Ca3Al2O6), Cch; calcium chloride hydroxide (CaClOH), Dic: dicalcium diiron oxide (Ca2Fe2O5), Dol: dolomite (CaMg(CO3)2), Geh: gehlenite (Ca2Al2SiO7), Hat: hatrurite (Ca3SiO5), Hyd: hydrocalumite (Ca2Al(CO3)0.25Cl0.5(OH)6(H2O)2.4), Kat: katotite (Ca3Al2(O4H4)3), Lar: larnite (Ca2SiO4), Lim: lime (CaO), May: mayenite (Al14Ca12O33), Non: nonacalcium tris (Ca9(Al2O6)3), Oxy: oxyapatite (Ca10(PO4)6O), Por: portlandite (Ca(OH)2), Qrz: quartz (a-SiO2), Ter: ternesite (Ca5(SiO4)2(SO4)), and Xon: xonotlite (Ca6Si6O17(OH)2).
diffraction pattern was obtained compared to that at low temperature heating. A total of 6 crystalline (calcite, gehlenite, hatrurite (Ca3(SiO4)O), larnite (Ca2(SiO4)), mayenite (Ca12Al14O33), and quartz) phases were identified in the diffraction pattern up to the 600 C treated samples as common phases. In contrast, the 1000 C heated samples contained 13 crystalline phases (andradite (Ca3Fe2(SiO4)3), anhydride, dicalcium diiron oxide (Ca2Fe2O5), dolomite (CaMg(CO3)2), gehlenite, hatrurite, larnite, mayenite, lime (CaO), nanocalcium Tris (Ca9Al2O6)3), oxyapatite (Ca10(PO4)6O), and quartz) by forming new crystalline phases upon crystallization of the amorphous phase. The concentration rate of insoluble radioactive cesium decreased to 24.8% and that of the amorphous phase was 4.7 mass% after the 1000 C treatment. Insoluble radioactive 137 Cs trapped in the inner amorphous phase or amorphous phases of different compositions was released by crystallization at 1000 C. A high correlation coefficient of R ¼ 0.9278 was observed between concentration rate of insoluble radioactive 137Cs and amorphous phase in MSWI fly ash at each heating treatment (Table 4). Therefore, insoluble radioactive cesium was contained in MSWI fly ash in three forms: free-radioactive cesium and those trapped in the surface and inner portion of the silicate amorphous phase. 4. Conclusion Radioactive cesium in MSWI fly ash contaminated by the FDNPP accident was analyzed by XRD and gamma-ray spectrometry. A total of 12 crystalline phases were identified in the diffraction pattern of raw MSWI fly ash, and the chloride-containing
137
Cs and amorphous phase content at each heating temperature.
Heating temperature/ C
Concentration rate of insoluble radioactive
Unheated 400 600 800 1000
100 76.4 76.4 45.6 24.8
137
Cs/%
Amorphous phase content/mass% 67.1 42.0 26.3 21.8 4.7
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compounds of halite and sylvite were dissolved via IE extraction using the sequential extraction method. In addition, approximately 60% of the radioactive cesium was dissolved in the IE fraction and was considered water-soluble radioactive cesium because the elution rate on IE fraction was similar to that obtained from the JLT13 with distilled water. The extraction rates of the other extraction fractions were quite low compared to the that of the IE fraction. Therefore, almost all soluble radioactive cesium was present in the form of chloride (CsCl) considering the elution behavior of chloride compounds. Radioactive cesium in MSWI fly ash could be separated to two forms, water-soluble as the chloride compound (CsCl) and insoluble forms. The insoluble radioactive cesium was confirmed using two approaches, chemical and heating treatments. The insoluble radioactive cesium composition in MSWI fly ash after the JLT-13 was confirmed using various chemical treatments. Insoluble radioactive cesium was eluted by hydrogen fluoride, and SiO2 concentration was significantly decreased. Therefore, almost insoluble radioactive cesium was contained primarily in silicate of amorphous or crystalline phases. MSWI fly ash after the JLT-13 was heated at several temperatures to determine the chemical form of the insoluble radioactive cesium. The relationship between the concentration rate of radioactive cesium and amorphous phase content in MSWI fly ash at each temperature exhibited good linearity (R ¼ 0.9278). The concentration rate of radioactive cesium was decreased in three distinct stages (untreated - 400 C, 600 Ce800 C, and 800 Ce1000 C) according to decreasing of amorphous content. Insoluble radioactive 137Cs was trapped into surface and inner part of the silicate amorphous phase as silicatebound and free radioactive cesium. This study provides a novel approach for the elution and removal of radioactive cesium for protecting the environment by controlling landfilled MSWI fly ash. CRediT authorship contribution statement Atsushi Ohbuchi: Writing - original draft, Writing - review & editing, Data curation. Kengo Fujii: Formal analysis. Miki Kasari: Formal analysis. Yuya Koike: Conceptualization, Supervision, Writing - review & editing. Acknowledgments The authors would like to thank Dr. Kiyoshi Nomura, Meiji University, for their continuing guidance and encouragement throughout this work. Appendix A. Supplementary data Supplementary data to this article can be found online at https://doi.org/10.1016/j.chemosphere.2020.126007. References Abollino, O., Aceto, M., Malandrino, M., Mentasti, E., Sarzanini, C., Petrella, F., 2002. Heavy metals in agricultural soils from Piedmont, Italy, Distribution, speciation and chemometric data treatment. Chemosphere 49, 545e557. https://doi.org/ 10.1016/S0045-6535(02)00352-1. Aubert, J.E., Husson, B., Sarramone, N., 2006. Utilization of municipal solid waste incineration (MSWI) fly ash in blended cement Part1: processing and characterization of MSWI fly ash. J. Hazard Mater. B136, 624e631. https://doi.org/ 10.1016/j.jhazmat.2005.12.041. Bogush, A., Stegemann, J., Wood, I., Roy, A., 2015. Element composition and mineralogical characterisation of air pollution control residue from UK energyfrom-waste facilities. Waste Manag. 36, 119e129. https://doi.org/10.1016/ j.wasman.2014.11.017. Chen, Z., Lu, S., Mao, Q., Buekens, A., Chang, W., Wang, X., Yan, J., 2016. Suppressing heavy metal leaching through ball milling of fly ash. Energies 9, 524e536. https://doi.org/10.3390/en9070524. Fan, Y., Zhang, F.S., Zhu, J., Liu, Z., 2008. Effective utilization of waste ash from MSW and coal co-combustion power plant-Zeolite synthesis. J. Hazard Mater. 153,
382e388. https://doi.org/10.1016/j.jhazmat.2007.08.061. Fujii, K., Ochi, K., Ohbuchi, A., Koike, Y., 2018. Evaluation of physicochemical properties of radioactive cesium in municipal solid waste incineration fly ash by particle size classification and leaching tests. J. Environ. Manag. 217, 157e163. https://doi.org/10.1016/j.jenvman.2018.03.028. Funari, V., Mantovani, L., Vigloitti, L., Tribaudino, M., Dinelli, E., Braga, R., 2018. Superparamagnetic iron oxides nanoparticles from municipal solid waste incinerators. Sci. Total Environ. 36, 119e129. https://doi.org/10.1016/ j.scitotenv.2017.11.289. Guirado, F., Gali, S., Chinchon, S., 2000. Quantitative Rietveld analysis of aluminous cement clinker phases. Cement Concr. Res. 30, 1023e1029. https://doi.org/ 10.1016/S0008-8846(00)00289-1. Harada, H., Yamamoto, T., Takaoka, M., 2011. Relation between chemical state and leaching property of lead in fly ash treated by mechanochemical method (in Japanese). Spring-8 Res. Rep. 1, 31e33. https://doi.org/10.18957/rr.1.2.31. Iwahana, Y., Ohbuchi, A., Koike, Y., Kitano, M., Nakamura, T., 2013. Radioactive nuclides in the incinerator ashes of municipal solid wastes before and after the accident at the Fukushima nuclear power plant. Anal. Sci. 29, 61e66. https:// doi.org/10.2116/analsci.29.61. Iwahana, Y., Ohbuchi, A., Koike, Y., Kitano, M., Nakamura, T., 2017. Speciation of the radioactive nuclides in incinerator fly ash of municipal solid waste using sequential extractions. J. Mater. Cycles Waste Manag. 19, 226e234. https:// doi.org/10.1007/s10163-015-0408-5. Koike, Y., Suzuki, R., Ochi, K., Hagiwara, K., Nakamura, T., 2017. Radioactivity analysis using commercially available chemical reagents as calibration sources. Bunseki Kagaku 66, 263e270. https://doi.org/10.2116/bunsekikagaku.66.263 (in Japanese). Komori, M., Shozugawa, K., Nogawa, N., Matsuo, M., 2013. Evaluation of radioactive contamination caused by each plant Fukushima Daiichi Nuclear Power Station using 134Cs/137Cs activity ratio as an index. Bunseki Kagaku 62, 475e483. https://doi.org/10.2116/bunsekikagaku.62.475 (in Japanese). Ministry of Environment, 2011. accessed. https://www.env.go.jp/jishin/attach/ waste-radioCs-16pref-result20110829.pdf. (Accessed 29 April 2017). Ministry of the Environment Government of Japan, 2015. Management and Treatment of Decontamination Wastes. FY2014 Decontamination Report, pp. 161e178. Nishida, K., Nagayoshi, Y., Ota, H., Nagasawa, H., 2001. Melting and stone production using MSW incinerated ash. Waste Manag. 21, 443e449. https://doi.org/ 10.1016/S0956-053X(00)00136-7. Ochi, K., Fujii, K., Hagiwara, K., Ohbuchi, A., Koike, Y., 2017. Characterization of radiocesium in soils sampled at the Koshinetsu and Kanto region. Bunseki Kagaku 66, 175e180. https://doi.org/10.2116/bunsekikagaku.66.175 (in Japanese). Ohbuchi, A., Ochi, K., Koike, Y., Nomura, K., Konya, T., Yamada, Y., Fujinawa, G., Nakamura, T., 2016. Composition and radio-cesium analysis of fly ash exhausted from incinerated general municipal waste in Fukushima prefecture. Adv. X-ray. Chem. Anal., Japan 47, 225e232 (in Japanese). Ohbuchi, A., Koike, Y., Nakamura, T., 2019. Quantitative phase analysis of fly ash of municipal solid waste by X-ray powder diffractometry/Rietveld refinement. J. Mater. Cycles Waste Manag. 21, 829e837. https://doi.org/10.1007/s10163-01900838-0. Okada, T., Matsuto, T., 2009. Determination of lead speciation in melting furnace fly ash by sequential chemical extraction. Chemosphere 75, 272e277. https:// doi.org/10.1016/j.chemosphere.2008.11.071. O’Connor, B.H., Raven, M.D., 1988. Application of the Rietveld refinement procedure in assaying powdered mixtures. Powder Diffr. 3, 2e6. https://doi.org/10.1017/ S0885715600013026. Pariatamby, A., Subramaniam, C., Mizutani, S., Takatsuki, H., 2006. Solidification and stabilization of fly ash from mixed hazardous waste incinerator using ordinary Portland cement. Environ. Sci. 13, 289e296. Qian, G., Song, Y., Zhang, C., Xia, Y., Zhang, H., Chui, P., 2006. Diopside-based glassceramics MSW fly ash and bottom ash. Waste Manag. 26, 1462e1467. https:// doi.org/10.1016/j.wasman.2005.12.009. , H., Corsaro, A., Hartmann-Koval, S., Juchelkov Raclavska a, D., 2017. Enrichment and distribution of 24 elements within the sub-sieve particle size distribution ranges of fly ash from wastes incinerator plants. J. Environ. Manag. 203, 1169e1177. https://doi.org/10.1016/j.jenvman.2017.03.073. Rietveld, H.M., 1969. A profile refinement method for nuclear and magnetic structures. J. Appl. Crystallogr. 2, 65e71. https://doi.org/10.1107/ S0021889869006558. Rosado, D., Usero, J., Morillo, J., 2016. Ability of 3 extraction methods (BCR, Tessier and protease K) to estimate bioavailable metals in sediments from Huelva estuary (Southwestern Spain). Mar. Pollut. Bull. 102, 65e71. https://doi.org/ 10.1016/j.marpolbul.2015.11.057. Saffarzadeh, A., Shimaoka, T., Kakuta, Y., Kawano, T., 2014. Cesium distribution and phases in proxy experiments on the incineration of radioactively contaminated waste from the Fukushima area. J. Environ. Radioact. 136, 76e84. https:// doi.org/10.1016/j.jenvrad.2014.05.009. Saikia, N., Kato, S., Kojima, T., 2007. Production of cement clinkers from municipal solid waste incineration (MSWI) fly ash. Waste Manag. 27, 1178e1189. https:// doi.org/10.1016/j.wasman.2006.06.004. Sakai, S., Mizutani, S., Takatsuki, H., Kishida, T., 1995. Leaching test of metallic compounds in fly ash of solid waste incinerator. J. Mater. Cycles Waste Manag. 6, 225e234. https://doi.org/10.3985/jswme.6.225 (in Japanese). Shiota, K., Takaoka, M., Fujimori, T., Oshita, K., Terada, Y., 2015. Cesium speciation in
A. Ohbuchi et al. / Chemosphere 248 (2020) 126007 dust from municipal solid waste and sewage sludge incineration by synchrotron radiation micro-x-ray analysis. Anal. Chem. 87, 11249e11254. https://doi.org/ 10.1021/acs.analchem.5b03298. Singh, G.V.P.B., Subramaniam, K.V.L., 2016. Quantitative XRD study of amorphous phase in alkali activated low calcium siliceous fly ash. Construct. Build. Mater. 124, 139e147. https://doi.org/10.1016/j.conbuildmat.2016.07.081. Steinhauser, G., Brandl, A., Johnson, T.E., 2014. Comparison of the Chernobyl and Fukushima nuclear accidents: a review of the environmental impacts. Sci. Total Environ. 470, 800e817. https://doi.org/10.1016/j.scitotenv.2013.10.029. Sukandar Padmi, T., Tanaka, M., Aoyama, I., 2009. Chemical stabilization of medical waste fly ash using chelating agent and phosphates: heavy metals and ecotoxicity evaluation. Waste Manag. 29, 2065e2070. https://doi.org/10.1016/ j.wasman.2009.03.005. Taylor, J.C., Hinczak, I., Matulis, C.E., 2000. Rietveld full-profile quantification of
9
portland cement clinker: the importance of including a full crystallography of the major phase polymorphs. Powder Diffr. 15, 7e18. https://doi.org/10.1017/ S0885715600010769. Tessier, A., Campbell, P.G.C., Bisson, M., 1979. Sequential extraction procedure for the speciation of particulate trace metals. Anal. Chem. 51, 844e851. https:// doi.org/10.1021/ac50043a017, 1979. Tojo, Y., Ishii, M., Matsuo, T., Shimaoka, T., 2014. Study on the existence form of hardly-soluble cesium contained in incineration bottom ash and its long-term stability. In: The Proceedings of the 25rd Annual Conference of Japan Society of Material Cycles and Waste Management. https://doi.org/10.14912/ jsmcwm.25.0_477. Toraya, H., 1990. Array-type universal profile function for powder pattern fitting. J. Appl. Crystallogr. 23, 485e491. https://doi.org/10.1107/S002188989000704X.