159

Experimental Study on the Mechanism of Cs Removal fromContaminated Soil and Incineration Ash by Pyroprocessing
Kazuo YAMADA1*, Kazuhiko TOKOYODA1, 2and Masahiro OSAKO3
Fukushima Branch, National Institute for Environmental Studies
10-2 Fukasaku, Miharu Town, Tamura-gun, Fukushima, 963-7700, Japan
2
Taiheiyo Cement Corporation
1-1-1 Koishikawa, Bunkyo-ku, Tokyo, 112-8503, Japan
3
Center for Material Cycles and Waste Management Research, National Institute for Environmental Studies
16-2 Onogawa, Tsukuba-city, Ibaraki, 305-8506, Japan*E-mail: yamada.kazuo@nies.go.jp
1

Abstract
After the Fukushima Daiichi nuclear power plant accident, a large region of northeastern Japan was
contaminated by radio-Cs (r-Cs). Contaminated soil and incineration ashes are generated throughdecontamination processes and daily human activities, respectively. To reduce the volume of such substances,
several kinds of pyroprocessing techniques have been developed. R-Cs is thought to be trapped within
aluminosilicates. With the addition of Ca to these compounds, alkali metals may be readily removed. Next, Cl
is added and the alkali metals are volatilized in the order of Cs > K > Na. On the basis of this estimation, thehighest Ca content is expected to produce the best conditions for the removal of Cs. Calcium silicate andaluminate with the highest Ca concentration are found in Portland cement. To understand the mechanism of
Cs volatilization, the effect of the Ca/(Si+Al) ratio on the ratio of Cs remaining is introduced on the basis ofdata from the literature. A high-efficiency Cs removal process in cement is also investigated using a small
scale rotary furnace for real contaminated soil and ashes, and by pilot-scale experiments with model soil.
Additionally, through detailed experiments using pollucite — a cesium aluminosilicate — Cs removal behaviors
were found to correspond to phase change, depending on the Ca/Si and Cl/Cs ratios. At high Ca/Si ratios,even without adding Cl, a significant amount of Cs could be removed. Potassium existing in or added to theinitially contaminated samples facilitated Cs removal such that Cs was reduced to an undetectable level even
without the addition of Cl.
Key words :	aluminosilicate, cesium removal, chloride volatilization, incineration ash, pollucite, Portland
cement, pyroprocessing, radio-cesium

1. Introduction
After the Fukushima Daiichi nuclear power plant(FDNPP) accident, a wide region of northeastern Japanwas contaminated with radio-Cs (r-Cs) (IAEA, 2015) .
Because of the nature of this accident, the majorcontaminant was limited to volatile r-Cs.
To reduce the additional radiation dose to 1 mSv/y,the target level determined by the Japanese government,
the surface soils in many regions surrounding the FDNPP
have been removed and are currently being transported to
an interim storage facility (ISF) (MOE, 2018a). From thissoil, combustibles are removed and sent to temporal
incinerators to reduce their volume; here, contaminatedincineration ash (IA) is generated. In addition, daily
human activities generate various kinds of wastes, suchas municipal solid waste (MSW) and sewage sludge,
Global Environmental Research
24/2020: 159-172
printed in Japan

which are then contaminated by r-Cs. In Japan, themajority of these wastes are sent to incinerators forvolume reduction; here, contaminated IA is also generated
in concentrated form. Because of the limited space in
ISFs, the volumes of this IA and relatively highly
contaminated soils must be reduced. For this purpose,
various technologies have been proposed in Japan for theremoval of Cs from these contaminated substances(JESCO, 2016 –2020). One of the most efficient methods
is based on chloride volatilization (Spalding, 1994).
Two major pyroprocessing systems using chloride
volatilization have been proposed; one involves the useof a melting furnace to reduce the volume of MSW-IA(Kamata et al., 2015), and the other involves a rotary kilnthat is used for Portland cement production (Tokoyoda
et al., 2018a). In both systems, a high temperature,
approximately 1,300ºC to 1,500ºC, is required. From both©2020 AIRES

160

K. YAMADA et al.

pyroprocessing systems, concentrated Cs is obtained as
CsCl salt. The decontaminated product obtained by themelting system is a slag, while that from the rotary kiln
system is a hydration-inactive sintered mineral
agglomerate or cement clinker (which is the raw material
used for Portland cement). These systems require quite
high temperatures, but the decontaminated products may
be used as commercial materials such as slag, sinteredagglomerates that may be used as aggregates, or Portland
cement. The management of decontaminated wastes is ofgreat importance. If it is difficult to find a use fordecontaminated materials, then a landfill site must be
used. In 2018, the Japanese Ministry of the Environment
ordered the construction of two kinds of pyroprocessing
systems, and in March 2020, the systems began operation(Yamada et al., 2020) although the rotary kiln system was
not adopted.
Considering the mechanism of Cs removal using
these pyroprocessing techniques, we note an interesting
report. After the FDNPP accident, intensive surveys ofvarious incinerators were conducted, and it was foundthat r-Cs tended to concentrate in fly ash rather than inbottom ash. The ratio of these concentrations depended
on the nature of the original combustible wastes (Yui etal., 2018; Fujiwara et al., 2017). When a significant
amount of Cl was included in the combustible wastes, theCs tended to become fly ash in a water-soluble form, suchas CsCl. Without Cl, Cs remained in aluminosilicate
form. This suggests that even at relatively low
temperatures such as 800ºC to 900ºC within incinerator
furnaces, chloride volatilization of Cs may occur. The
melting and boiling temperatures of CsCl are 645ºC and1,295 ºC, respectively. Exceeding the boiling temperatureof CsCl is not needed to achieve volatilization, and some
vapor pressure of CsCl may be estimated enough at such
low incineration temperatures.
According to previous reports on pyroprocessing
systems for volume reduction of IA and contaminatedsoils (Kamata et al., 2015; Tokoyoda et al., 2018a;
Honma et al., 2014; Manpuku et al., 2017), r-Cs is
assumed to exist within clay, pollucite and glass minerals,
and others. The phases containing Cs are assumed to bealuminosilicates. As was determined experimentally(Kamata et al., 2015; Tokoyoda et al., 2018b; Honma etal., 2014; JAEA, 2011; MOE, 2018b) by adding CaO and
CaCl2, the majority of Cs in an aluminosilicate may bevolatilized at an appropriately high temperature. The
mechanism of Cs volatilization can be assumed asfollows:- In an aluminosilicate, cations exist within thismaterial depending on its mineralogical structure,and its cation content varies significantly.
- By adding a large amount of CaO to such analuminosilicate, alkali metal oxides including Cs2O
may be easily released from the aluminosilicate
structure by replacement of Cs with Ca.

- Upon addition of Cl, excess alkali metals oxides
form alkali chlorides and these phases exhibit
significant vapor pressures at high temperatures that
may be lower than the boiling temperature of Cs2O.
- Alkali metals transition from solid to vapor phases atthese temperatures. The tendency of volatilization ofalkali metals follows the order of Cs > K > Na; Cs,
including r-Cs, is therefore preferentially volatilized.
- The vapor may then be cooled in a cooling system
and recrystallized as solid alkali chlorides, which arecollected in a bag filter system. From the flue gas
following this bag filtration, the r-Cs content in theflue gas is reduced to undetectable levels even whenusing a high-volume sampler.
Considering the above-mentioned concepts, higher
ratios of Ca/(Al+Si) and Cl/Cs should be suitable forpromoting the removal of r-Cs from IA and soil. From theviewpoint of a high Ca/(Al+Si) ratio, the use of Portland
cement provides the most favorable system. In this study,a series of experimental investigations on the effects of
the Ca/(Al+Si) and Cl/Cs ratios for Cs removal from
pollucite (CsAlSi2O6) were conducted to elucidate theremoval mechanism of Cs via pyroprocessing treatments.
These were done after reviewing the characteristic
mineral combination of Portland cement.

2. Chemical Reactions in Portland Cement
Production
To understand the mechanisms underlying theformation of the minerals considered in this paper, a basic
understanding of Portland cement must be introduced.
Portland cement is one of the largest industrially
produced materials. It is a mixture of burned minerals,
known as cement clinker, and calcium sulfate. The basic
components of cement clinker are 3CaO∙SiO2 (known asalite), 2CaO∙SiO2 (known as belite), 3CaO∙Al2O3, and
4CaO∙Al2O3∙Fe2O3, which have mass fractions of roughly65, 20, 7.5, and 7.5 w/w% (mass percent), respectively.
These mass fractions are determined on the basis of thetotal balance of performance of the Portland cement usedin concrete.
3CaO∙SiO2 and 3CaO∙Al2O3 are the most Ca-richsilicate and aluminate minerals in the CaO–SiO2–Al2O3
ternary system. Upon burning of the raw powders ofthese materials and after the decarbonation of CaCO3 toform free lime, 2CaO∙SiO2 crystals and the Ca–Al–Fe–O
liquid phases are generated within the temperature rangeof 900ºC to 1,300ºC. At temperatures of 1,300ºC to
1,450ºC, 2CaO∙SiO2 reacts with free lime to form
3CaO∙SiO2. The amounts of the Ca–Al–Fe–O liquid
phases affect the formation speed of 3CaO∙SiO2, whichmust be controlled within an appropriate range. This
reaction does not proceed well when these quantities are
too small. When these quantities are too large, the burnedmaterial adheres to the inner surface of the kiln, and theExperimental study on the mechanism of Cs removal from contaminated soil and incineration ash by pyroprocessing 161
products are not discharged from the kiln. After burning,
the burned materials, known as clinker, which arecomposed of particles a few centimeters in diameter, aresent to a cooler. Rapid cooling is important for thestabilization of the high-temperature phases of 3CaO∙SiO2
and 2CaO∙SiO2. 2CaO∙SiO2 may be stabilized as
β-2CaO∙SiO 2 via rapid cooling, but thethermodynamically stable phase is γ-2CaO∙SiO2, which
does not express hydration reactivity. The Ca–Al–Fe–O
liquid phase constitutes a matrix (known as an interstitial
phase) of these calcium silicates, and with a decrease intemperature, this liquid phase crystallizes into two
different phases, 3CaO∙Al2O3 and 4CaO∙Al2O3∙Fe2O3.
The chemical compositions are shown in the CaO–
SiO2–Al2O3 ternary phase diagram with the chemicalcomposition of ordinary Portland cement (Fig. 1). In
actual cement, alkali metals and sulfur at quantities on theorder of 0.1 w/w% exist as contaminants that derive fromthe raw materials. Na exists mainly in 2CaO∙SiO2 andorthorhombic 3CaO∙Al2O3, while K exists mainly in alkali
sulfate. In 2CaO∙SiO2, more cations may be contained ascompared with 3CaO∙SiO2. 3CaO∙Al2O3 is known to haveboth orthorhombic and cubic crystalline structures. Whenthe alkali/sulfur molar ratio exceeds 1.0, the excess
amount of alkali materials is included in orthorhombic
3CaO∙Al2O3.
In modern production processes for cement, with the
exception of typical raw materials including limestone,
silica sand, clays and the iron and heat sources provided
by coal, a large variety of wastes are used as raw
materials and alternative fuels. Only the chemicalcompositions of the raw materials for the production ofPortland cement must be controlled. There is no need tocontrol either the mineral or chemical forms of thesematerials. During thermal processing at approximately
1,450ºC, all components are decomposed to form clinker

Mole fraction SiO2

CaO‒Al2O3 ‒SiO2 T=1400℃, P=1.01325bar

Mole fraction Al2O3

Fig. 1 CaO–SiO2 –Al2O3 ternary phase diagram at 1,400ºC withclinker mineral compositions (modified according to aprevious study from Research Institute of Computational
Thermodynamics Inc.).

minerals. A typical alternative heat source is processed
MSW, in which vinyl chlorides are included. When Cl isincluded in a raw material, potassium is preferentiallyvolatilized as KCl in rotary kilns. In general, thevolatilizing tendencies of alkali chlorides follow the orderof Cs > K > Na, and the boiling temperatures of thesematerials follow the order of 1,295 < 1,420 < 1,465ºC.
However, the Cs content of cement is assumed to be 1 to
10 ppm, which is much less than that of K, which is on
the order of 0.1 w/w%. Because of the volatilization
tendencies and the molar ratios of the existing elements,
the ratio of Cs remaining in Portland cement is not easily
estimated and should be examined in real systems.
The behaviors of alkali elements and Cl in Portland
cement production are similar to those in the incinerators
for MSW, which both involve chloride volatilization fromalkali materials. However, differences exist in theprocessing temperatures and Ca content.
In Japan, a unique type of Portland cement plant has
been introduced, known as “eco-cement,” because morethan half of the raw materials that are used are wastes
such as IA rich in Cl. The Cl content of cement must be
controlled because Cl may cause steel corrosion when
Portland cement is used in reinforced concrete. In an ecocement system, Cl is removed via the volatilization ofalkali chlorides by adding alkali carbonates. Without theaddition of alkali elements, Cl forms a calcium
chloroaluminate liquid phase at burning temperatures ofover 1,350ºC, and in this phase, alkali metals may
dissolve. Therefore, the volatilization behaviors of alkali
chlorides have been of great interest in the cement
industry.

3. Cs Removal in Pyroprocessing
3.1 
Literature Review of Several Systems for the
Removal of Cs
In nature, r-Cs is thought to be fixed within clay
minerals (Manpuku et al, 2017) and is difficult to remove
via simple heating processes (Honma et al., 2019). As
explained in Chapter 1, the addition of a sufficientamount of Ca to aluminosilicate may aid this removal
process. On the basis of three previous studies (Kamata etal., 2015; Tokoyoda et al., 2018a; Honma et al, 2014)
discussing the effects of adding CaO and CaCl2 at varying
Ca/(Si+Al) ratios and temperatures, the removal of Cs
through various pyroprocessing techniques was therefore
studied.
Honma et al. (2014) investigated several types ofcontaminated soil with a maximum r-Cs concentration of
25 kBq/kg. By adding CaO and CaCl2 and heating the
mixture to 1,350ºC, they were able to reduce the r-Cs
content of the pyroprocessed materials to 50 Bq/kg. The
performance of this system was also demonstrated usinga large-scale rotary kiln with a 10 t/day capacity (Honma
et al., 2019; Tokoyoda et al, 2018b). By adjusting theK. YAMADA et al.

Ca/Si and Cl/K ratios and temperature, the r-Cs
concentrations in soils contaminated with 21 kBq/kg of
r-Cs and incineration ashes with contamination levels of
1 to 111 kBq/kg were successfully reduced to less than
100 Bq/kg (the clearance level) in the majority of thetested batches. These operations were carried out in 26
runs from May 2018 to January 2019, for 470 t ofcontaminated soil and ashes. The amounts ofcontaminated wastes were reduced by approximately one
tenth. In this system, the Cl content was controlled interms of the K concentration ratio of the contaminatedsamples because Cs is considered to be more easily
volatilized than K. If the Cl content is sufficient tovolatilize K, then all of the Cs may volatilize. Moreover,
the applicability of the decontaminated samples as
aggregates for civil engineering works or concrete was
examined in their study.
Kamata et al., 2015 demonstrated the highperformance of a different system involving a surface
melting furnace. The optimized parameters of that weresimilar to those of the rotary kiln system described above.
The differences between the two systems pertain to thematerials obtained after decontamination. The former
process mainly results in 2CaO∙SiO2 and gehlenite, while
the latter produces slag. By adjusting the processparameters and by considering model soil and ashes
containing 0.2 w/w% of stable Cs, a 99.9% removal of Cs
was achieved. In this system, the chemical compositions
were adjusted to result in a sufficient amount of alkali
elements with Cl/K molar ratios ranging from 4.6 to 22 inorder to obtain a molten phase at 1,400ºC.
Tokoyoda et al. (2018b) examined the performanceof a Portland cement system at laboratory scale using realcontaminated materials. They used a larger rotary kiln
with an inner diameter of 450 mm, length of 8,340 mm,
and capacity of 30 kg/h using a model soil containing
0.1 w/w% of stable Cs. To obtain the cement clinker,
the Ca/Si molar ratio was controlled to around 3.0. The
Cl/K molar ratio was controlled at 1.0, as performed by
Honma et al., 2014.
The chemical compositions of the materials
examined by the three studies are shown in Fig. 2 for the
CaO–SiO2–Al2O3 ternary system at 1,400ºC. As shown, awide range of chemical compositions were examinedwhile considering the melting system. In the rotary kiln
system, two chemical compositions were examined. One
was a typical hydration reactive Portland cement, while
the other involved non- or less-hydration reactive
minerals.
In Fig. 3, the ratios of Cs remaining to the respective
original concentrations of the treated materials are plottedagainst the Ca/(Si+Al) molar ratio. Kamata et al. (2015)
proposed an optical basicity considering various elements
as an additional index because other minor elements may
behave as cations or anions. For example, under oxidizing
conditions, Fe may behave similarly to Al. P2O5 can

CaO‒Al2O3 ‒SiO2 T=1400℃, P=1.01325bar

Mole fraction SiO2

162

Mole fraction Al2O3

Fig. 2 Chemical compositions examined in previous studies(data points are plotted on the CaO–SiO2 –Al2O3 diagramat 1,400 ºC). Blue: Kamata et al., 2015, Red: Honma
et al., 2014), Green: Tokoyoda et al., 2018a.

Fig. 3 Relationship of the ratio of Cs remaining from contaminatedsources to the Ca/(Si+Al) molar ratio. The legend refers toreference sources and pyroprocessing temperatures from
Kamata et al. (2015), Honma et al. (2014) and Tokoyoda etal. (2018a).

participate in calcium silicates as part of the silicate. As
shown in the above figure, a higher Ca/(Si+Al) ratio
results in a lower ratio of Cs remaining. For the Portland
cement composition utilized by Tokoyoda et al. (2018a),
Cs was reduced to an undetectable level. However, as thedetection limit was 0.01%, the actual efficiency may behigher than was indicated in this study. As indicatedabove, the Ca ratio in terms of cation capacity inaluminosilicates appears to be a key factor that is
independent of the pyroprocessing system. Judging fromthe aforementioned results, we expect Portland cement toprovide the best chemical composition for removal of Csfrom various sources.
As a decontamination material, cement composed of

Experimental study on the mechanism of Cs removal from contaminated soil and incineration ash by pyroprocessing 163
model soil at 1,450ºC demonstrated normal performanceas Portland cement, satisfying Japanese Industrial
Standard JIS R 5210: 2019 (Tokoyoda et al., 2018a).
3.2 Detailed Effects of Temperature and Cl/K Ratios
in a Portland Cement System
3.2.1 Experiments
From the discussion in the former chapter
considering the system with the highest Ca concentration,
Portland cement is expected to provide a highly efficientsystem for removing Cs. The effects of temperature and
Cl/K ratio from the viewpoint of the ratio of Cs remaining
may next be examined on the basis of data provided by
Tokoyoda et al. (2018b) with additional IA data.
The samples used in this study were obtained fromresidential land soils, pond deposits and incineration fly
and bottom ashes generated in Fukushima Prefecture. The
chemical compositions and radiation concentrations of
r-Cs in the examined samples are shown in Table 1. The
examined samples are examples of real contaminatedmaterials that require treatment, but because of limited
capacity to treat radioactive materials in our laboratory,
only samples with relatively low contamination levels
were used. Therefore, the detection ability for
determining the removal efficiency of the overall system
was also limited. The chemical compositions for theexperiments were adjusted to those of Portland cement byusing reagent-grade free lime (CaO) and CaCl2, as well as
commercial silica sand. The target mineral compositions
were 60, 20, and 20 w/w% for 3CaO∙SiO2, 2CaO∙SiO2,
and 3CaO∙Al2O3-4CaO∙Al2O3∙Fe2O3, respectively.
The major factors examined were the types ofsamples, heating temperature and Ca/Si and Cl/K ratios.
The pyroprocessing conditions are shown in Table 2. The

samples were ground, mixed and then heated in a rotary
furnace. The homogeneous heating zone was φ = 50 ×
120 mm. The samples were heated at a rate of 5ºC/min
and maintained at their respective target temperatures for
60 min.
Radioactivity was measured by using a Ge detector,
and other major elements were measured by X-ray
fluorescence (XRF) analysis. The detection limit ofradioactivity depends on measurement time; hence, thedetection limits in this study varied from 3 to 15 Bq/kg
depending on the available machine time.
From X-ray diffraction/Rietveld analysis, the mineralcompositions determined for the samples 3CaO∙SiO2,
2CaO∙SiO2, 3CaO∙Al2O3, and 4CaO∙Al2O3∙Fe2O3 treated at
1450ºC were 62, 21, 6, and 10 w/w%, respectively. At
this temperature, we confirmed that the target clinker
minerals formed.
3.2.2 Results
1) Effects of temperature
Figure 4 shows the effects of the pyroprocessing
temperature on the ratio of Cs remaining. In this series,
the Cl/K molar ratio was controlled at 1.0, and theamount of Cl was controlled at an excess in terms of theCs content. The ratio of Cs remaining was calculated
from the original irradiation concentration and thatexisting after pyroprocessing. The detectable ratio of Cs
remaining depended on the original value and detection
limit. This is the reason for the wide variation in thedetection limits shown in Fig. 4.
Under these conditions, the amounts of all alkali
metals were also reduced at higher temperatures. The
order of the ease of removal was Cs > K > Na, as
expected even under conditions of their significantly
different concentrations. Cs was reduced to undetectable

Table 1 Chemical compositions of the examined materials.
Chemical composition (w/w%)

Bq/kg

Sample

SiO2

Al2O3

Fe2O3

CaO

MgO

SO3

Na2O

K2O

P2O5

Cl

Ig.Loss

Total

r-Cs

Residential land soil

21.26

5.83

2.03

64.20

0.92

0.07

0.82

0.78

0.10

0.59

7.43

104.02

793

Pond deposits

18.29

3.56

2.31

53.08

0.34

0.00

0.21

0.34

0.10

0.55

35.94

114.692250

Incineration fly ash

20.37

3.36

4.47

58.54

0.62

1.59

0.30

1.19

0.15

0.89

9.12

100.606819

Incineration bottom ash

21.83

4.93

2.00

63.93

0.90

0.12

0.72

1.14

0.23

0.86

2.72

99.38

8198

Table 2 Experimental conditions.
FactorSample type andtemperature

Ca/Si, Cl/K, andtemperature

Sample

Ca/Si

Cl/K

Temp. (ºC)

Residential land soil

3.0

1.0

1200, 1250, 1300,
1350, 1400, 1450

Pond deposits

3.0

1.0

1200, 1250, 1300,
1350, 1400, 1450

Incineration fly ash

3.0

1.0

1400

Incineration bottom ash

3.0

1.0

1400

Residential land soil

3.0

0.0, 0.2, 0.5, 1.0

1400

Residential land soil

2.20.0, 1.1

1400

Pond deposits

3.0

0.0, 1.0

1450

164

K. YAMADA et al.

levels at temperatures higher than 1,300ºC. The
volatilizations of the alkali metals did not occur in theorder of Cs > K > Na, but rather simultaneously. Only theratios of each element differed. Although the ratios of K
and Na remaining depended on the sample type, those of
r-Cs were similar for all subjects. Simply all data were
below the detection limit and the differences were
thought to be unobservable. Residential land soil andbottom ash samples demonstrated similar behaviors. The
pond deposits showed much lower ratios of Na and K
remaining, and the fly ash exhibited the smallest values.
The mechanisms underlying these removal processes areunclear.
2) Effects of the Cl/K ratio
Figure 5 shows the effects of the Cl/K molar ratio on
the ratio of Cs remaining. In this series, the temperature
was modified to 1,400ºC or 1,450ºC, and the Ca/Si molar
ratio was modified to 3.0 or 2.2. A ratio of 3.0 is requiredfor Portland cement, while 2.2 is required for an
aggregate. The order of ease of alkali metal volatilizationis the same as that shown in Fig. 4. Cs is the most easily
volatilized, followed by K and Na, which are much lesseasily volatilized. All alkali metal concentrations werereduced by increasing the Cl/K ratio.
At 1,450ºC, without the addition of Cl, the ratio of
Cs remaining decreased to the detection limit. The
mechanism of volatilization is unclear, but Cs may bevolatilized as Cs2O. At 1,400ºC without Cl, 2.8% and5.6% of Cs remained at Ca/Si ratios of 3.0 and 2.2,
respectively. In both cases, Cs was reduced to thedetection limit by increasing the Cl/K ratio.

4. E
 ffects of Ca/Si and Cl/Cs Ratios on Behaviorof Cs from Pollucite at High Temperatures
4.1 Use of Pollucite
As seen in the discussion above, the optimal
conditions for the removal of Cs from various sourceswere determined. The Cs content was very limited and it
was difficult to clarify the behavior of Cs in the solidphase materials. Therefore, pollucite, which is a Cs
aluminosilicate (CsAlSi2O6), was used in this study to
examine the detailed behaviors of Cs during
pyroprocessing.

Fig. 4 The effects of temperature on the ratios of remaining alkali
metals. (Circles indicate residential land soil and triangles indicate
pond deposits.)

4.2 Experiments
4.2.1 Materials
Pollucite was synthesized according to processdescribed in a previous study (Kobayashi et al., 1991).
The chemical composition of the synthesized pollucite
analyzed by XRF analysis is shown in Table 3. The X-ray
diffraction (XRD) pattern of the obtained pollucite isshown in Fig. 6. All peaks of the obtained material
matched the standard data for cubic pollucite well.
4.2.2 Experimental conditions
As explained in the previous chapters, the additionof CaCl2 and CaO is important for removing Cs. The
combined effects of these additions at a temperature
range of 900ºC to 1,100ºC were reported by Jiao et al.

Fig. 5 The effects of the Cl/K ratio on the ratios of alkali metals
remaining. (Circles indicate residential land soil and triangles
indicate pond deposits.)

Table 3 Chemical composition of the synthesized pollucite (w/w%).
Ig. loss

SiO2

Al2O3

Fe2O3

CaO

MgO

SO3

Na2O

K2O

Cs2O

P2O5

Cl

Total

0.29

37.9

16.3

0.02

<0.01

0.0

<0.01

0.12

0.04

39.7

0.00

0.00

99.81

Experimental study on the mechanism of Cs removal from contaminated soil and incineration ash by pyroprocessing 165(2018). In this series of experiments, the generation ofcommercially valuable slag, aggregate, or Portland
cement as decontaminated products was examined using
an applied temperature reaching 1,450ºC.
The chemical composition parameters examined
were the Ca/Si and Cl/Cs ratios. The Ca/Si molar ratios
were set at 3.3, 2.2 and 1.0, and the Ca/(Si+Al) molar
ratios were set at 2.4, 1.6 and 0.72, respectively, with theassumption of the formation of a cement clinker, nonhydration reactive aggregate and slag, respectively. To
retain the appropriate amount of liquid phase at theburning temperatures, the Si/(Al+Fe) ratio was also
controlled at 2.2, 2.1 and 2.0, respectively, for each of theaforementioned products.
To adjust the chemical compositions for eachpurpose, reagent-grade CaO and CaCl2, as well as silica
sand, were added to the synthesized pollucite. Minor
elements such as Fe, Na and K were brought from thesilica sand. Under each condition, the Cl/Cs molar ratio
was modified to range from 0.0 to 5.0.
Pyroprocessing was carried out using the same rotary
furnace described in Sub-section 3.2.1. The heating
temperature was 1,450ºC, which was maintained for
60 min. The temperature was increased at a rate of
5ºC/min. The volatilized materials were recollected ina HEPA filter from the exhaust gas after cooling.
Sampling from the HEPA filter was carried out following
all experiments, but was not performed for each batch.
4.2.3 Measurements
The chemical compositions of the pyroprocessedmaterials were measured by XRF. The mineral phasecompositions of these materials and the phase changes
that occurred during heating were evaluated qualitatively
by XRD. To conduct the high-temperature XRD analysis,
the temperature was increased at a rate of 10ºC/min from
25ºC (room temperature) to 1,400ºC, and measurements
were performed at every 100ºC increment. The scanning
range of 2θ was from 5º to 65º, and the scanning speed
was 50º/min. For observing the formed textures of thepyroprocessed materials, back-scattered electron imaging

Fig. 6 X-ray diffraction (XRD) pattern of the synthesized cubic pollucite.

(BEI) was used. The chemical composition of each phaseincluding element distributions was analyzed by electronprobe micro analyzer (EPMA).
4.3 Results
4.3.1 Cs Volatilization Behaviors
The effects of the Cl/Cs ratio on the ratio of Cs
remaining at different Ca/Si ratios after pyroprocessing at
1,450ºC are shown in Fig. 7. The Cl/Cs ratio affects theratio of Cs remaining differently at different Ca/Si ratios.
Without the addition of Cl (i.e., at a 0.0 Cl/Cs molar
ratio), a higher Ca/Si ratio results in a lower ratio of Cs
remaining.
At a Ca/Si ratio of 1.0, without added Cl, almost of
all the Cs remained in the solid phase. By increasing the
Cl/Cs ratio from 0 to 1.0, the ratio of Cs remaining was
decreased to 3%.
At a Ca/Si ratio of 2.2, the effects of Cl/Cs werelimited to the range of less than 0.4. With an increase in
the Cl/Cs ratio to 0.6, the ratio of Cs remaining decreased
from 16 to 8%. When the Cl/Cs ratio was increased to
1.1, the ratio of Cs remaining became less than 0.06%.
When the Ca/Si ratio was 3.4, even without theaddition of Cl, the ratio of Cs remaining was 4.8%, and it
decreased to less than 0.06% at a Cl/Cs ratio of 1.0.
Therefore, a higher Ca/Si ratio resulted in a lower
ratio of Cs remaining, as was expected.
4.3.2 Phases Generated after Pyroprocessing
To investigate the reactions occurring during
pyroprocessing, the phase composition was evaluated via
XRD. The material obtained in the filter system of theexhaust gas after all experiments was pure CsCl, as
shown in Fig. 8. This finding, however, does not deny thepossibility of Cs2O formation because Cs2O reacts
strongly with water to form CsOH. Because CsOH ishighly deliquescent, it is difficult to detect via XRD.

Fig. 7 Cs volatilization in terms of the Cl/Cs ratio at different
Ca/Si ratios (1,450 ºC).

166

K. YAMADA et al.
○：Ca3SiO5 (Alite, 00-055-0739)
×：β-Ca2SiO4 (Carnite, 01-076-3608)△：Ca3Al2O6 (00-038-1429)
×◇：CaO (Lime, 01-077-9574)
××□：Ca12Al14O32Cl2 (00-029-0407)

(a)

×

×

Intensity[a.u.]

×

×
××
×

× ×

×

×

Cl/Cs=1

×Fig. 8 XRD pattern of material collected from the exhaustgas filter.

Cl/Cs=5

×

10

20

30

40

50

60

2θ[°](CuKα)(b)

×：β-Ca2SiO4 (01-076-3608)＋：γ-Ca2SiO4 (01-070-2450)★：Cs2Ca2Al8O15 (00-041-0536)▲：Ca12Al14O32Cl2 (00-029-0407)

××

Intensity[a.u.]

★

×

×

×

★

★ ★★× ×× ×★
×★ × ＋ × ×★ ×
★ × ×
★ ××★ ★★
★
★
★ ×
★
×★
＋

▲

＋

＋
＋

×

×

▲

＋×

＋ ▲

×

×＋＋
×

＋

×

10

×

×

▲

20

×

＋× ＋▲
＋

＋

＋
＋ ＋

▲

＋
＋×

▲

▲
▲

▲

＋

×

×

＋

×
＋
＋
＋
＋×＋ ▲ ＋
×
×

×
×

▲

×★
××
★
××

Cl/Cs=1

▲

×

＋

▲

＋

▲

＋

＋
＋ ＋

Cl/Cs=0

× ×
×
×
× ×
× ×
×× ★ ★× ★× ××

＋

×

▲

＋

▲×

× ×

30

Cl/Cs=5

×

×

×
▲
▲
××××××▲＋× ××＋××
× ×× × ×

40

50

60

2θ[°](CuKα)

(c)
◎
◎

×：Ca2SiO4 (Calcio-olivine, 01-087-1257)◎：CsAlSiO4 (Orthorhomic, 00-031-0346)◎

Intensity[a.u.]

Figure 9 shows the XRD patterns of thepyroprocessed materials at 1,450ºC. At a Ca/Si ratio of
3.4 (Fig. 9(a)), the original pollucite content was reduced
to zero for all Cl/Cs ratios, and typical clinker mineralssuch as Ca3SiO5 and β-Ca2SiO4 were identified. Hereafter,
chemical compositions are described in total, such as
Ca3SiO5, and not as separate components such as
3CaO∙SiO2. The phase composition of the interstitial
phase, however, varied with the Cl/Cs ratio. At Cl/Cs
ratios of 0 and 1, Ca3Al2O6 was identified, while at a ratio
of 5, Ca12Al14O32Cl2 was identified.
Figure 9(b) shows the XRD patterns for a Ca/Si ratioof 2.2. At all Cl/Cs ratio values, the original pollucitecontent disappeared while the identified mineralcompositions differed depending on the Cl/Cs ratio.
Without the addition of Cl, the major phases identified
were β-Ca2SiO4 and Cs2Ca2Al8O15. As the Cl/Cs ratio
increased to 1.0, the crystalline form of Ca2SiO4 changed
from β to γ. This is suitable for use as a pyroprocessed
product such as a non-hydration-reactive aggregate.
Moreover, the phase containing Cs disappeared as expectedfrom Fig. 7 and Ca12Al14O32Cl2 was detectable. At a higher
Cl/S ratio (5.0), the crystalline form of Ca2SiO4 changed
from γ to β again, but the amount of this form decreased
compared to Fig 9(a). The interstitial phase, Ca12Al14O32Cl2,
was identified as possessing an amorphous phase, which
was suggested by a hollow region at 2θ ≈ 32º.
Figure 9(c) shows the XRD patterns at a Ca/Si ratioof 1.0. Without the addition of Cl, a limited amountof Ca2SiO4 (in different crystalline forms from Figs. 9(a)and 9(b)) formed, while the majority of the material
was unreacted pollucite as expected from Fig. 7. The
crystalline form of pollucite changed from a cubic stablestate at room temperature to an orthorhombic stable state
at higher temperatures. With the addition of increasing
amounts of Cl, only the amorphous phase without any
crystalline phases was detected.

Cl/Cs=0

×
× ×
×
× ××
×
× ××

×

◎

◎

×
×

◎

×××
×

×

◎
◎ ◎

×
◎

×

×
×
×
×
×

◎

◎
× ◎
◎ ◎◎
◎

× ×
×

◎

Cl/Cs=0

◎×

◎

◎◎
◎

Cl/Cs=1
Cl/Cs=5
10

20

30

40

50

60

2θ[°](CuKα)Fig. 9X
 RD patterns of the pyroprocessed material at 1,450ºC.
PDF-2 numbers are shown in parentheses.
		(a) Ca/Si ratio = 3.4,
		(b) Ca/Si ratio = 2.2,
		(c) Ca/Si ratio = 1.0.

Experimental study on the mechanism of Cs removal from contaminated soil and incineration ash by pyroprocessing 167
4.3.3 Decomposition of Pollucite with Increasing
Temperature
The decomposition of pollucite and phase changes
were dependent on both the Ca/Si and Cl/Cs ratios. To
understand the decomposition behaviors of pollucite,high-temperature XRD analysis was utilized for several
combinations of Ca/Si and Cl/Cs ratios and the obtained
results are shown in Fig. 10, showing only the major peakof pollucite.
At a Ca/Si ratio of 3.4 and a Cl/Cs ratio of 1.0, thepollucite peak disappeared at 1,000ºC with a slight shift
at 900ºC. When the Ca/Si ratio was decreased to 2.2 at asimilar Cl/Cs ratio, the peak remained until 1,100ºC.
Therefore, a greater Ca content facilitates thedecomposition of pollucite at lower temperatures. When
the Cl/Cs ratio was decreased to 0.6, the peak remained
Ca/Si
=3.4
(Cl/Cs
=1.0)

Ca/Si
=2.2
(Cl/Cs=1.1)

until 1,300ºC, even at a Ca/Si ratio of 3.4. In the case of a
Ca/Si ratio of 2.2, we observed a peak shift at 900ºC, but
the peak remained until 1,300ºC. Cl may therefore also
play an important role in the decomposition of pollucite.
 extures of Mineral Phases after Pyroprocessing
4.3.4 T
Considering the observed Cs removal behaviors andphase changes analyzed by XRD, we carried out direct
observations and compositional analysis of the textures ofthe mineral phases formed after pyroprocessing.
Figure 11 shows a BEI of the pyroprocessed material
at a Ca/Si ratio of 3.4 and a Cl/Cs ratio of 0. Three major
phases are indicated: many rectangular and small,rounded gray particles; small, round white spots within
the gray particles, and a darker matrix. Figure 12 shows
the EPMA mapping of the same area. As indicated, thewhite spots correspond to high concentrations of Cs.
Ca/Si
=3.4
(Cl/Cs
=0.6)

Ca/Si
=2.2
(Cl/Cs
=0.6)

Fig. 10 Changes in the XRD peaks of pollucite with increased temperature.

Fig. 11 Back-sacttered electron imaging (BEI) of the pyroprocessed material (Ca/Si ratio = 3.4, Cl/Cs ratio = 0).

Fig. 12 Electron probe micro analyzer (EPMA) mapping of elements (same area as Fig. 11; warm colors such as white or
red indicate higher concentrations).

168

K. YAMADA et al.

The chemical compositions of these three phases
analyzed by EPMA are shown in Table 4. From theanalysis data and with utilization of the major elements,
the molar ratios are also indicated. Point A of therectangular phase is considered to be Ca3SiO5, the major
clinker phase. Point B of the matrix is essentiallyconsidered to be Ca3Al2O6, as estimated from the resultsof XRD, but 5 mol % of aluminate is replaced withsilicate. The white spots (C) indicate cesium calcium
aluminosilicate. From the texture of the region
surrounded by Ca3SiOs, the white spots may be remnantsof the original pollucite particles that decomposed during
pyroprocessing. Because of the limited area of thesespots, no clear diffraction pattern could be obtained by
XRD. From Fig. 7, 4.8 w/w% of Cs remained after

pyroprocessing. Judging from the texture shown in
Fig. 11, the reason Cs remained can be surmised as Cs
bearing phases remained in the crystalline 3CaO.SiO2
phases and Cs was prevented from volatilizing but not as
an issue of phase equilibrium. Therefore, if the raw
materials are ground finer, the ratio of Cs remaining may
decrease more.
Figure 13 shows a BEI analysis of the pyroprocessedmaterial at a Ca/Si ratio of 2.2 and a Cl/Cs ratio of 0.
Figure 14 shows an EPMA mapping of the same area.
From these figures, three phases can be distinguished:large gray rounded particles, white rectangular grains at
the grain boundary of the gray particles, and a small
amount of a dark matrix. In Table 5, the chemicalcompositions of these phases are shown. Points A, B and

Table 4 Chemical compositions of the three phases (A, B, and C) shown in Fig.11 (upper: w/w%; lower: mol %).
Position

SiO2

CaO

Al2O3

Fe2O3

MgO

Na2O

K2O

Cs2O

P2O5

Cl

Total

A

25.26

72.12

0.81

0.02

0.34

0.02

0.02

0.00

0.02

0.00

98.61

B

4.61

58.37

29.03

0.43

1.02

0.14

0.03

0.00

0.02

0.01

93.64

C

13.96

44.48

22.19

0.14

0.29

0.06

0.01

18.56

0.00

0.00

99.68

Position

SiO2

CaO

Al2O3

Cs2O

Total

A

24.5

75.0

0.5

0.0

100.0

B

5.5

74.2

20.3

0.0

100.0

C

17.8

60.6

16.6

5.0

100.0

Fig. 13 BEI of the pyroprocessed material (Ca/Si ratio = 2.2, Cl/Cs ratio = 0).

Fig. 14 EPMA mapping of elements (same area as indicated in Fig. 11; warm colors such as white or pink indicate
higher concentrations).

Experimental study on the mechanism of Cs removal from contaminated soil and incineration ash by pyroprocessing 169
C, indicating the white grains, have similar chemicalcompositions and are considered to be cesium calcium
aluminate. We identified Cs2Ca2Al8O15 from XRD fitting,while the results obtained by EPMA differed. This phase
may be some solid solution of different Cs/Ca ratios. The
compound cesium calcium aluminate is therefore thought
to have formed from the pollucite, CsAlSi2O6. The Cs
containing phase was transformed from aluminosilicate
to calcium aluminate. There are two types of grayparticles in different crystalline phases indicated from theresults obtained by XRD and represented as the samechemical composition of Ca2SiO4 by points D and E.
Point F in the dark matrix indicates Ca12Al14O33 gehlenite,
but the quantity was limited and undetectable by XRD.
Figure 15 shows a BEI of the pyroprocessed material
at a Ca/Si ratio of 3.4 and a Cl/Cs ratio of 5. Figure 16
shows an EPMA mapping of the same area. From thesefigures, three phases can be distinguished: gray

Table 5 Chemical compositions of the six points indicating the two phases (A, B, C, D, E, and F) shown in Fig. 13 (upper:
w/w%; lower: mol%).
Position

SiO2

CaO

Al2O3

Fe2O3

MgO

Na2O

K2O

Cs2O

P2O5

Cl

Total

A

0.59

18.53

38.82

0.20

0.08

0.15

0.12

26.45

0.03

0.01

84.97

B

1.59

17.88

39.37

0.18

0.00

0.25

0.08

26.13

0.00

0.00

85.48

C

0.83

17.83

39.82

0.19

0.09

0.22

0.14

26.98

0.01

0.00

85.21

D

33.02

63.94

1.01

0.07

0.18

0.04

0.03

0.00

0.03

0.00

98.33

E

32.55

64.57

1.14

0.04

0.16

0.04

0.02

0.00

0.07

0.00

98.60

F

5.37

45.11

38.63

0.62

1.75

0.22

0.08

0.00

0.01

0.00

91.79

Position

SiO2

CaO

Al2O3

Cs2O

Total

A

1.2

40.5

46.7

11.5

100.0

B

3.2

38.7

46.9

11.2

100.0

C

1.7

38.9

47.8

11.7

100.0

D

32.3

67.1

0.6

0.0

100.0

E

31.8

67.6

0.7

0.0

100.0

F

7.0

63.2

29.8

0.0

100.0

Fig. 15 BEI of the pyroprocessed material (Cs/Si ratio = 3.4, Cl/Cs ratio = 5).

Fig. 16 EPMA mapping of elements (same area as shown in Fig. 15; warm colors such as pink or red indicate
higher concentrations).

170

K. YAMADA et al.

rectangular particles, darker gray dendritic particles and abright matrix. Table 6 shows the chemical compositionsof these phases. Point A, indicating gray rectangularparticles, represents Ca3SiO5. Point B, indicating darker
gray particles, represents Ca2SiO4. Point C, indicating thebright matrix, represents calcium chloroaluminosilicate.
From the results obtained by XRD analysis, this phase
was identified as Ca12Al14O32Cl2, although the actual
chemical composition was found to contain a greater
amount of Cl, and some Al2O3 was replaced by SiO2.
Figure 17 shows a BEI of the pyroprocessed material
at a Ca/Si ratio of 2.2 and a Cl/Cs ratio of 5. Figure 18
shows an EPMA mapping of the same area. From thesefigures, four phases can be distinguished: small amounts ofa dark phase between the interparticle spaces; gray, roundparticles; and darker-gray, irregularly shaped particles

showing exolution and a bright matrix. In Table 7, thechemical compositions of these phases are shown. Point
A, indicating the dark phase, represents calcium
chloroaluminosilicate (Ca12Al14O32Cl2) as detected by the
XRD analysis, but with a greater Cl content. Point B,
indicating a gray round particle, represents Ca2SiO4. Point
C, indicating a darker-gray, irregularly shaped particle,
represents calcium chloroaluminosilicate with a low Cl
content. According to the texture of these particles, they
may be composed of multiple phases such as Ca2SiO4 and
Ca12Al14O32Cl2. Point D, indicating the bright matrix, also
represents calcium chloroaluminosilicate, but with alower aluminate content and greater silicate content ascompared with point A. This phase is surmised to be an
amorphous phase, as detected by XRD.

Table 6 Chemical compositions of the three phases (A, B, and C) shown in Fig. 15 (upper: w/w%; lower: mol%).
Position

SiO2

CaO

Al2O3

Fe2O3

MgO

Na2O

K2O

Cs2O

P2O5

Cl

A

25.30

73.14

0.51

0.01

0.23

0.00

0.01

0.00

0.06

0.04

99.30

B

32.08

64.04

0.99

0.01

0.10

0.00

0.02

0.00

0.09

0.23

97.56

C

8.03

61.35

9.11

0.28

0.00

0.00

0.05

0.00

0.03

26.31

105.17

Position

SiO2

CaO

Al2O3

Cl

Total

A

24.3

75.3

0.3

0.1

100.0

B

31.6

67.5

0.6

0.4

100.0

C

6.5

53.1

4.3

36.0

100.0

Total

Fig. 17 BEI of the pyroprocessed material (Cs/Si ratio = 2.2, Cl/Cs ratio = 5).

Fig. 18 EPMA mapping of elements (same area as shown in Fig. 17; warm colors such as white, pink and red
indicate higher concentrations).

Experimental study on the mechanism of Cs removal from contaminated soil and incineration ash by pyroprocessing 171
Table 7 Chemical compositions of the four phases (A, B, C, and D) shown in Fig. 17 (upper: w/w%; lower: mol%).
Position

SiO2

CaO

Al2O3

Fe2O3

MgO

Na2O

K2O

Cs2O

P2O5

Cl

Total

A

8.54

44.07

33.43

0.05

0.00

0.01

0.01

0.00

0.04

10.01

96.14

B

33.67

64.79

0.08

0.00

0.11

0.00

0.04

0.00

0.11

0.04

98.84

C

30.07

60.34

5.54

0.00

0.10

0.00

0.00

0.00

0.06

2.74

98.84

D

26.76

50.78

3.45

0.17

0.00

0.00

0.03

0.00

0.07

21.14

102.40

Position

SiO2

CaO

Al2O3

Cl

Total

A

9.2

51.1

21.3

18.3

100.0

B

32.6

67.3

0.0

0.1

100.0

C

29.3

63.0

3.2

4.5

100.0

D

22.5

45.7

1.7

30.1

100.0

4.4 Discussion
To achieve removal of Cs from pollucite, thismaterial must first be decomposed. The Ca/Si,
Ca/(Si+Al), and Cl/Cs ratios affect the decomposition
process; higher values of these quantities result in moreadvanced decomposition. At low Ca/Si ratios and without
Cl, pollucite is stable and no Cs is removed. When the
Ca/Si ratio is adequately high, a Cl/Cs ratio of 1.0 iseffective for the complete removal of Cs. However, as the
Cl/Cs ratio is increased at a low Ca/Si ratio, a Clcontaining glass phase forms and alkali metals including
Cs may dissolve into this phase, thereby preventing thecomplete removal of Cs. These complicated phenomena
are related to the formation of different mineral phases
depending on the Ca/Si and Cl/Cs ratios. Therefore, theaddition of too much Cl may produce undesired results;
an appropriate amount of Cl is recommended for use athigh Ca/Si ratios.
In Section 3.2, we showed that Cs was removed toundetectable levels from pond deposits without theaddition of Cl. A significant amount of Cs resulting from
pollucite remained, however. This difference may be
accounted for by the existence of potassium. Considering
the samples examined in Section 3.2, we included around
1 w/w% of potassium and determined the amount of Cl
using the Cl/K ratio. This means that Cl/Cs is in excess,and the excess Cl volatilizes as KCl and no glass phaseforms. Potassium acts as an accelerant in Cs removal.
Cs removal under high Ca/Si ratio conditions may beachieved by simple volatilization of Cs2O, but Cl
volatilization is not always required. Considering theexperimental results, we consider a higher Ca/Si ratio tobe preferential for the efficient removal of Cs.

Ca/(Si+Al) ratio was used to produce slag and Portland
cement.
The dependence of the Cs removal efficiency on the
Ca/(Si+Al) ratio was shown on the basis of data obtained
from the literature.
The highest Ca/(Si+Al) ratio could be realized in thesystem producing Portland cement. The optimal
conditions of pyroprocessing were then examined. We
showed that higher temperatures and a higher Cl/K ratio
are preferential for Cs removal from various
contaminated wastes. All kinds of alkali metals were
removed with different efficiency, and Cs levels werereduced preferentially, with the ease of volatilization
following the order of Cs > K > Na at 1450ºC, even
without the addition of Cl. Potassium in the target
subjects is considered to act as an accelerant for theremoval of Cs.
The effects of the Ca/Si and Cl/Cs ratios on mineralphase changes were analyzed through experiments using
pollucite. A higher Ca/Si ratio was observed to facilitate
the decomposition of pollucite and the efficient removalof Cs.

5. Conclusions

Fujiwara, H., Kuramochi, H., Nomura, K., Maesato, T. and Osako,
M. (2017) Behavior of radio cesium during incineration ofradioactively contaminated wastes from decontamination
activities in Fukushima. Journal of Environmental Radioactivity.
178–179, 290–296. https://doi.org/10.1016/j.jenvrad.2017.08.014
Honma, K., Takano, H., Miura, K., Sasaki, T., Kimura, T. andManpuku, Y. (2014) Removal of Cs from the soil
contaminated with radioactive materials by heat treatment.

We discussed efficient conditions for Cs removalfrom radioactive solids contaminated by r-Cs, such as soil
and incineration ashes, via pyroprocessing. Afterdecontamination, the resulting materials may be
preferentially used for other purposes. Therefore, a target

Acknowledgment
This study was conducted in collaboration with the
National Institute for Environmental Studies, Taiheiyo
Cement Corp., and the National Agriculture and Food
Research Organization.
The discussion with Mr. Kenichi Honma of Taiheiyo
Cement Corp. was very helpful to summarize this study.
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172

K. YAMADA et al.

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Kazuo YAMADAAs a materials scientist with a specialty incement-related materials, Kazuo Yamada, whoholds a doctorate of engineering, works at the
Wastes and Material Cycles Research Section of
the Fukushima Regional Collaborative ResearchCenter, National Institute for Environmental
Studies (NIES). He joined NIES in 2012 and has
worked on technologies for reducing the volume of contaminated soil andwastes, and on safe disposal of concentrated wastes in concrete facilities.
He is also active in the Society of Remediation of Radioactive
Contamination in the Environment as secretary of a research committee ontechnological strategies for final disposal of nuclear wastes out of
Fukushima.

Kazuhiko TOKOYODA
Kazuhiko Tokoyoda holds a master ofengineering. He was formerly a special researcher
at NIES’ Fukushima Branch (currently renamed
the Fukushima Regional Collaborative ResearchCenter). He is a mechanical/chemical engineer
with experience in the construction and operationof various production facilities at Taiheiyo
Cement Corp. spanning more than 20 years. He joined NIES in 2017 andhas worked there for three years, focusing especially on optimization andmechanism analysis of Cs volatilization by pyroprocessing in Portland
cement production systems.

Masahiro OSAKO
Masahiro Osako, who holds a doctorate ofengineering, serves as director of the Material
Cycles Division, National Institute forEnvironmental Studies (NIES). His specialty isenvironmental engineering, focusing on waste
management. Since the Fukushima nuclear
accident that resulted from the Great East Japan
Earthquake in 2011, he has been dedicated not only to conducting various
researches to properly manage radioactively contaminated wastes but also
to playing an important role in the relevant policy-making by the national
government. He also chairs the research committee on technologicalstrategies for the final disposal out of Fukushima in the Society of
Remediation of Radioactive Contamination in the Environment.
(Received 4 August 2020, Accepted 27 December 2020)