金属イオンを含む亜臨界水による汚染土壌からのCs回収ーー水熱条件下での粘土鉱物からのCs脱離促進ーー

東京工業大学科学技術創成研究院

原子燃料サイクル研究ユニット

○ 竹下 健二、Xiang-Biao Yin

1

T

TO

T

TO

T: tetrahedral sheet O: octahedral sheet

Weathered 2:1 clays

Cs Adsorption on Clay Minerals in Contaminated Soil

Various clay minerals in soils

Illite/muscovite/biotite

2:1 dioctahedral type2:1 trioctahedral type

vermiculite/smectite

Mg Fe

Mg Fe

Important clay minerals in Fukushima

Dominant adsorptive clay minerals

Frayed edge site(10.7 Å)

Vermiculite, illite

•Takes long time to access•Once Cs is trapped, no escape•Small ratio to whole charge•Main cause of Cs entrapment

Phyllosilicate (Sheet of SiO4 tetrahydra) has siloxane ditrigonal cavity similar to the size of Cs

2

HAADF-STEM image of Cs treated phlogopiteCs adsorbed muscovite

Cs is selectively sorbed by vermiculite-like clay minerals and fixed on various binding sites such as planar/frayed edge/interlayer sites.

Hiroki Mukai, etc. Environ. Sci. Technology. 2014, 48, 13053-13059. James P. Mckinley, etc. Environ. Sci. Technology. 2004, 38, 1017-1023. Kenji Tamura, etc. Environ. Sci. Technology. 2014, 48, 5808-5815.

Edge-removal for radioactive Cs-biotite

Cs adsorption in soil and distribution on clay particles

1.o-

1.4n

m

(H. Mukai, et al. 2016) (J. P. Mckinley, et al. 2004) (K. Tamura, et al. 2014)

(H. Mukai, et al. 2016)

3

Research Groups Year Clay/soil Extraction Agent Condition Removal Ratio

K. Morimoto, et al. 2012 Vermiculite 3 M Mg2+ 25℃ 70~90%

H. Mukai, et al. 2015 Fukushima biotite 1M NH4+, Cs+, Mg2+,

0.1M H+ 25℃ Mg2+:58 %NH4

+:5.1%M. Yanaga, et al. 2015 Soil 2M K+ 25℃ 75%K. Murota, et al. 2016 Soil 0.001~0.1M K+ 25℃, 140d 60%L. Dzene, et al. 2015 Vermiculite 1M NH4

+ 25℃ 30%D. Parajuli, et al. 2015 Soil 0.5M H+ 95~200℃ 50~95%

C. Liu, et al. 2003 Sediments 3M Na+, K+, Rb+, 0.5M NH4

+ 25℃,134d 27~80%

N. Kozai, et al. 2012 Fukushima soil 1M NH4+,1M H2SO4 25℃ 40%

A. De Koning, et al. 2004 Illite 1M NH4+ 25℃ 56%

C. Willms, et al. 2004 Illite Alkylammonium salt 25℃ 45%I. Shimoyama, et al. 2014 Vermiculite Mixed NaCl-CaCl2 620~800℃ 40% (3min)

Problems/under discussion

Recent studies about Cs removal from clay/soil

2. Mono/divalent ions have varied roles1. Cs was poorly and partially removed3. High ion strength/temp were used 4. Desorption kinetics were very slow

Sublimation

4

Objectives

Reversibility of Cs+

on clay mineralsAdsorption Desorption

To improve the Csdesorption ratio.To clarify the

mechanism of Csdesorption.

To clarify Cs sorptionbehavior on claysTo prepare samples

similar with Cssimulated soil

Frayed edge site(10.7 Å)

Vermiculite, illite

5

4 6 8 100

200

400

600

800

1000

1200

Ori Vermiculized biotite

2θ / o(CuKα)

Inte

nsity

10.1Å

12.0Å

12.4Å

14.3Å

25Å

Characterizations of used Sample - Vermiculitized Biotite

Compositions (wt. %)SiO2 46.1MgO 24.9Fe2O3 8.61Al2O3 13.0K2O 5.55CaO 0.57TiO2 1.25

SEM XRF

XRD

BSE

Structure formula is (Si3.14Al0.86)O10(Al0.18Ti0.06Fe0.15Mg2.53)(OH)2(K0.48Ca0.04). VB occurs interstratificated structure with Mg-layers and K-layers.

Mg-vermiculite layer K-biotite layer

6

Cs Adsorption Experiment

Cs+ LiquidSolid

Shaking

After centrifugation, measuring with AAS

AAS

Vermiculitized biotite (VB)

Batch adsorption (25 ℃ )

Drying(85℃, 24h) Separate

Solid-liquidWash and sieve

Cs Con: 10ppm -2000ppm; S/L: 0.1g/10ml; T: 25℃; t:2 d

Adsorption capacity, Q

𝑸𝑸 =𝑪𝑪𝒊𝒊 − 𝑪𝑪𝒆𝒆

⁄𝑺𝑺 𝑳𝑳Where:Co is the initial Cs concentrationCe is the equilibrium Cs concentrationS/L is the solid-to-liquid ratio.

SEM-EDX XRDd： basal spacing

7

7

Cs Adsorption on VB

4 6 8 10

Inte

nsity

(arb

uni

t)

2θ/ o (CuKα)

Ori

50ppm

100ppm

200ppm

300ppm

500ppm

1000ppm

12.0Å

11.9Å

11.6Å11.9Å

11.2Å

10.7Å

10.7Å 2000ppm

10.7Å 0.5M

10.1Å12.0Å

12.4Å14.3Å25Å

25 Å: Regular interstratification of Mg and K layer 14.3 Å: Hydrous Mg2+ layer 12.4 Å: Partial hydrous Mg2+ layer 12.0 Å: Random interstratification of Mg and K layer 10.6 Å: Cs collapsed layer 10.1 Å: Biotite K+ layer

The peak for Mg layer gradually disappears with Cs sorption increase.

The peak for K layer shows no change. The disappearance is attributed to the

transition from Mg-vermiculite layers to Cs-substituting layers.

Mg2+

Mg2+ → Cs+

K+ 10.1 Å

14.3 Å M M

K K K K KTOT

TOT

TOT

M MM

Cs+K CsK+ Mg2+M H2O

KK K2:1 Layer δ- δ-δ-δ-δ-

2:1 Layer δ- δ-δ-δ-δ-

2:1 Layer δ- δ-δ-δ-δ-

CsK K K K K K K

10.7 Å

2:1 Layer

2:1 Layer

2:1 Layer

TOT

TOT

TOT

Cs CsCs

10.1 Å

Cs CsCsCs

Cs Cs Cs

Cs Cs CsCs δ- δ-δ-δ-δ-

δ- δ-δ-δ-δ-

δ- δ-δ-δ-δ-

8

Usage of Cs Saturated VB as Contaminated Soil

0

300

600

0

300

600

0 1 2 3 4 5 6 7 8 9 10

Cou

nts

(a.u

.)

Energy (keV)

1

2

CsFe

Mg

Ti

KAl

Si

Ca

O

Cs

VB used in the present study is capable of adsorbing 2.44 wt. % of CsO (35.8 mg/g).

Sorbed Cs is almost homogeneouslydistributed within collapsed interlayers.

Frayed edge site(10.7 Å)

Trace amount of Cs in FES

9

Hydrothermal Treatment (HTT) using Subcritical Water

→ Cs adsorbed in organic materials canbe recovered to water phase by thedecomposition of organic materials.

① High-speed Hydrolysis Effect

Ionic product of water becomes larger insubcritical state under high temperature(200-280℃) and high pressure (3-4 MPa).

Ionic Product and Conductivity of WaterTemperature [℃]

Con

duct

ivity

[-]

Conductivity Ionic Product

log

Kw

(ion

ic p

rodu

ct)

T [℃]

P[M

Pa]

374100

Icewater

critical point

0.1

22

watervapor

subcritical water

（supercritical water）

Water Phase Diagram

Specific Chemical Properties of Subcritical Water

② High-speed Ion Exchange Effect→ Cs adsorbed in inorganic materials

can be recovered to aqueous phaseby promoted ion exchange withvarious cations in subcritical water. 10

Cs Desorption by Hydrothermal Treatment (HTT)

Ionic Product and Conductivity of WaterTemperature [℃]

Con

duct

ivity

[-]

Conductivity Ionic Product

log

Kw

(ion

ic p

rodu

ct)

T [℃]

P[M

Pa]

374100

Icewater

critical point

0.1

22

watervapor

subcritical water

（supercritical water）

HTT Desorption (100-250 oC, ＜4 Mpa)

Pressure Vessel

Pressure Gauge

Sample

Thermo-couple

catalysis

11

3 4 5 6 7 8 9 100

300

600

900

1200

1500

10.7Å

25Å

Inte

nsity

(arb

uni

t)

2θ/ o (CuKα)

ori VB Cs collapsed VB HTT 0.01M NH4 HTT 0.01M Na HTT 0.01M K HTT 0.01M Mg HTT 0.01M Ca

11.1Å10.1Å

12.0Å

12.4Å

14.3Å

Mg2+/Ca2+

K+/Na+/NH4+

Enhanced Cs desorption by HTT with M2+ Cation

Cs is still rarely desorbed by monovalent cations.

High temperature greatly enhances the Cs desorption by divalent cations.

XRD results confirms that Mg2+ indeed substitutes Cs+ from its collapsed interlayer.

Mg2+/Ca2+ expands the collapsed interlayer.X.Yin et al., J Hazard Mate, Vol. 326, pp. 47-53, 2017

0

20

40

60

80

100

CaCl2MgCl2KClNaCl

Deso

rptio

n ra

tio (%

)

Cations (0.01M)

5th time HTT (0.5 h) 4th time HTT (0.5 h) 3rd time HTT (0.5 h) 2nd time HTT (0.5 h) 1st time HTT (0.5 h)

NH4Cl

250 oC

Cs collapsed VB

K K K K

Cs Cs Cs Cs10.7 Å

10.1 Å

MK CsK+ Cs+ Mg2+, Ca2+

0

20

40

60

80

100

Deso

rptio

n ra

tio (%

)

Cations (0.01M)

1st time (50h) 2nd time (50h) 3rd time (50h) 4th time (250h)

CaCl2MgCl2KClNaClNH4Cl

25 ℃Mg

M+

12

Cs Desorption from Cs-VB at Varied Temp

Cs desorbed amount was dependent on thetreating temperature.

Higher temp enhanced Mg2+ diffusionwithin collapsed interlayers, resultingdesorption of more Cs+ from center region .

100 150 200 2500

20

40

60

80

100

Des

orpt

ion

ratio

(%)

Temperature (oC)

0.01M, Mg2+ A

B

C

Cs-VB

HTT 150oC

HTT 250oC

13

Cs Desorption from Cs-VB by Mg2+ at different Conc.

0

25

50

75

100

Deso

rptio

n ra

tio (%

)

MgCl2 (mol/L)

(AT 25 oC) 1st 2nd 3rd 4th 5th

0

25

50

75

100

Deso

rptio

n ra

tio (%

)

(HTT 250 oC) 1st 2nd 3rd 4th 5th

310.10.01

4 6 8 10

2θ/ o (CuKα)

10.1Å

12.0Å12.4Å

14.3ÅRaw-VB25Å

10.1ÅCs-VB10.1Å

11.2~10.7Å

11.2Å11.2Å

11.5Å10.1Å10.1Å

11.8Å14.3Å

AT 0.1M

AT 3M 11.8Å

12.4Å12.0Å14.3Å

10.1Å10.1Å

10.1Å

14.3Å

14.3Å

a

bcdefg

14.3Å

Inte

nsity

(arb

uni

t)

12.4Å 750 cps

h

i

j

AT 0.01M

AT 1M

HTT 0.01M

HTT 0.1M

HTT 1M

HTT 3M 12.0Å

Total desorption ratios improves withthe increase of concentration of Mg2+.

14

A

B

C

Cs-VB

HTT 150 oC

HTT 250 oC

Cs Desorption by HTT with Mg2+

Cs-saturated VB Cs-desorbed VB

After HTT at 150 oC, partial Cs in center area is not removed.

After HTT at 250 oC, all Cs in both edge and center is removed.

Mg2+ diffuses into collapsed interlayers from near-edge to interior central region with increase of treating temperature.

15

Enhanced Cs Desorption by HTT with M3+ Cations

4 6 8 10

Ori -VB

10.1Å

11.9Å12.4Å

14.3Å25Å

10.1Å

11.2~10.7Å

10.7Å

11.4Å

10.8~10.4Å

14.3Å12.4Å

12.0Å

11.8Å

12.3ÅHTT 0.01M Al

14.2Å

12.4Å14.0Å

HTT 0.01M Fe

Cs-VB

HTT 0.01M NH4

HTT 0.01M Na

HTT 0.01M K

HTT 0.01M Mg

HTT 0.01M Ca

10.1Å

10.1Å

10.1Å

10.1Å

10.1Å

a

bcde

f

g

500 cps

h

i

15.2Å

HTT 0.01M La j

Inten

sity (

arb u

nit)

2θ/ o (CuKα)

0

20

40

60

80

100

La3+Fe3+Al3+Ca2+Mg2+Na+

Deso

rptio

n ra

tio (%

)

Chloride salts (0.01M)

5th time HTT 4th time HTT 3rd time HTT 2nd time HTT 1st time HTT

K+NH4+

Monovalent cations

Divalent cations

Trivalent cations

M3+ (Al3+/Fe3+/La3+) have the stronger ability to desorb Cs than that of M2+/M+.

XRD confirms the substitution process.

250 oC

16

Cs Desorption by HTT with Al3+

100 150 200 250

0

20

40

60

80

100

0.1M

0.01M

Deso

rptio

n ra

tio (%

)

Temperature (oC)

5th time HTT 4th time HTT 3rd time HTT 2nd time HTT 1st time HTT

0.001M 0.1

M0.0

1M0.0

01M 0.1M

0.01M

0.001M 0.1

M0.0

1M0.0

01M

4 6 8 1010.1Å

12.0Å

12.4Å14.3Å25Å

10.6Å1000ppm Cs+

11.6Å0.01M AlCl3

0.01M AlCl3 HTT150℃

14.0Å11.7Å

0.01M AlCl3 HTT200℃

12.3Å12.3Å

0.01M AlCl3 HTT250℃

2θ/ o (CuKα)

14.0Å

14.0Å0.1M AlCl3 HTT250℃

Inte

nsi

ty (

arb u

nit

)Ori

Cs-Verm

HTT100℃

Same as Mg2+, desorption ratiosimproves with the increase of Al3+

concentration and temperature. XRD confirms the expansion of

interlayers after Al3+ extraction. 17

Cs Desorption by HTT with Al3+

Cs+ Saturated VB

K+ layer

Cs+ layer10.7 Å

10.1 Å

Cs+ Desorbed VB

Al+ layer

Al+ layer

14.0 Å

14.0 ÅAl+ HTT

Ion Exchange

Cs+ substitution by Al3+

150 oC

K+ substitution by Al3+

250 oC0.01M

0.1M

18

Cs Desorption for Actual Contaminated Soil

0 20 40 60 800

100

200

300

400

5 10 150

100

200

300

Q

Q,B

Inte

nsity

(arb

uni

t)

2θ/ o (CuKα)

Contaminated Soil (＜2 mm) Contaminated Soil (＜75 µm) Non-Cs Soil (＜2 mm) Non-Cs Soil (＜75 µm)

QQQQ

BBVV

10.1Å14.3Å

12.5o

VBV

8.9o6.3o

VBV

HTT: 0.5g/50ml, 30 min

Actual contaminated soil is samplednear a gutter inlet in Tokaimura,Ibaraki Prefecture.

XRD confirms the existence of weathered micaceous clay in soil.

Radioactivity: 15,500 Bq/kg

19

Cs Desorption from Radioactive Fukushima Soil

HTT with 0.5 M Mg2+ at 60 oC is not useful for Cs desorption. Decomposition of Cs-sorbed organic material releases 25% of Cs. Cs desorption is significant enhanced by HTT with Mg2+ at 250 oC. M3+ (Fe3+/Al3+ ) cations indeed desorb more Cs than M2+ (Mg2+).

0

20

40

60

80

100

60 oC

0.50

Deso

rptio

n ra

tio (%

)

Mg2+ Concentration (M)

HTT 250oC 1st time 2nd time 3rd time

0.5

250 oC

250 oC

0

20

40

60

80

100

Deso

rptio

n ra

tio (%

)

Cations (0.5M)AlCl3FeCl3MgCl2

78 83 86

20

60 oC

Mechanism Discussion

① Before Cs+ adsorption, Mg2+ and K+ originally occupy the interlayers② During Cs+ adsorption, Cs+ gradually replace Mg2+ in frayed edge sites.③ Edge of interlayer region collapsed and Cs diffused into deeper region④ By HTT, M2+/M3+ expanded collapsed layer again and readily replace Cs+. 21

Summary and Conclusion

1. Cs+ is successfully fixed in collapsed interlayers bysaturation sorption to simulate its tight fixation on FES ofclay mineral into soil.

2. Higher temp can significant enhance M2+/3+ to desorb Cs+

from collapsed interlayer regions of clay minerals.

3. Mechanism underlying the desorption process of Cs bydivalent cations and the applicability of the hydrothermaltreatment to remove trace amounts of Cs from actualradioactive soil are clarified.

22

THANK YOU FOR YOUR ATTENTION!

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