Colloid Facilitated Transport ofRadioactive Cesium in a Fukushima Soil.

Nov. 04, 2013

Taku NishimuraDepartment of Biogical and Environmental EngineeringGraduate School of Agricultural and Life SciencesThe University of Tokyo

2

Why we need to consider colloids in Cs transport?

• Chemically, Cs is less hydrated and thus prefer tobound with soil particles.

• Transport of ionic Cs is very slow.

• Alternative process may be considered

– inorganic colloids facilitated

– organic colloids facilitated

• Migration of soil colloids in a Fukushima soil waslimited (Mizoguchi, 2013)

3

Kashiwagi and Sakuma (1995)

Source of radioactive Cs was nuclear experimentsin atmosphere during 1960’s.

Use radioactive Cs as a tracer to evaluate soil loss.A rolling hill in northern Japan (Hokkaido).

Deposition ofsediments

Source ofsediments

44

Ishikawa et al. 2007Radioisotopes56: 519-528

Large Kd of radio-active Cs in Japanese soils

solutiondadsorb CsKCs

5

From Soil Physics 6th ed. by Jury and Horton

Time (h)

ddR 1 K

Kd=1000 L/kg →R≒2000

Typical ground water recharge: 400(mm/y)×30(yrs)=12000mm

Kd and retardation factor, R

→ 6mm/30yrs

6

#2

#1

#3

May 2013, Myojindake (明神岳)Iitate, Fukushima

In Fukushima region, 70% of land iscovered by forest.Annual precipitation is around 1200mmTemp. ranges -2 to 30 ℃ (13 ℃ in average)

Upslopewith litter

Foot of slopewithout litter.

Source of sediments

Gentle slope.Depositional

area.

FukushimaNuclear PP-I

7

0

5

10

15

20

25

30

0.E+00 5.E+04 1.E+05 2.E+05

De

pth

(cm

)

Radioactive Cs (Bq/kg)

#4

③800007700

⑦94003300

⑪120001100

⑩360003500

⑨430002200

⑧226000111000

①28300082000

---

②53000020000

site Numbertop 0-2cm [Bq/kg]middle 2-4cm [Bq/kg]Green 4-6cm

0

5

10

15

20

25

30

1.E+00 1.E+02 1.E+04 1.E+06

De

pth

(cm

)

Radioactive Cs (Bq/kg)

#10

0

5

10

15

20

25

30

1.E+00 1.E+02 1.E+04 1.E+06D

ep

th(c

m)

Radioactive Cs (Bq/kg)

#2

④4100013700064000

8

0

5

10

15

20

25

30

1 100 10,000 1,000,000

De

pth

(cm

)

Radioactive Cs Bq/kg

#8C/N

#1C/N

#2C/N

0

5

10

15

20

25

30

0 10 20 30 40

De

pth

(cm

)

TC %, C/N

#8TC

#1TC

#2 TC

#8C/N

#1C/N

#2C/N

0～16cm 0～16cm

y = 913.81e0.3459x

R² = 0.9637y = 56.588e0.2074x

R² = 0.9397

1.0

10.0

100.0

1000.0

10000.0

100000.0

1000000.0

0.0 10.0 20.0 30.0 40.0 50.0

TC %

#1,2

#8

指数 (#1,2)

指数 (#8)

y = 0.0179e0.6285x

R² = 0.4365

1.0

10.0

100.0

1000.0

10000.0

100000.0

1000000.0

0.0 5.0 10.0 15.0 20.0 25.0 30.0

C/N %

#1,2

#8

指数 (#1,2)

Upslope with litter layer. No soil loss.

Rad

ioac

tive

Cs

Bq/k

g

9

0

5

10

15

20

25

30

1 100 10,000 1,000,000

De

pth

(cm

)

Radioactive Cs Bq/kg

#7TC

#10TC

#11TC

#12

0

5

10

15

20

25

30

0 10 20 30 40

De

pth

(cm

)

TC %, C/N

#12TC#11TC#10TC#7TC#12C/N#11C/N#10C/N#7C/N

0～16cm 0～16cm

Foot of slope without surface litter

Rad

ioac

tive

Cs

Bq/k

g

y = 33.915e0.3995x

R² = 0.4431

1.0

10.0

100.0

1000.0

10000.0

0.00 2.00 4.00 6.00 8.00 10.00 12.00

TC %

#7,10,11,12 exclude depositted

y = 0.123e0.4284x

R² = 0.513

1.0

10.0

100.0

1000.0

10000.0

0.0 5.0 10.0 15.0 20.0 25.0C/N

#7,10,11,12 exclude depositted

10

Suspension derived from the Myojin litter

De-ionized water：約1000 mL

Litter from Myojin forest. ：44 g（Cs： 3.09×105 Bq/kg-dry）

Sieve <53 mm

Settle to fractionateparticles smaller thanStokes diameter of 1 mm

Further disintegration by H2O2

and heating..

Cs： 1189 Bq/L

Cs： 1056 Bq/L

Suspension A

Suspension B

Use NaI counter to measure 134Cs and137Cs (Wizard 2480, Perkin Elmer)

11

Suspension extractedfrom litter of a forestin Myojin

Particle size distribution of suspension passed 0.45μm-filter

What caused greater movement of the Cs

Particle size [μm]

Intensity

oflaserdiffraction[%]

12

Suspension A

Suspension B

Radio. Cs suspended particle size

5cm settlement for 16hrs 1189Bq/kg (1μm)Centrifuge (10000rpm,1hr) sediment: 1189Bq/kg -Centrifuge (10000rpm,1hr) supernatant: ND 0.2μm

（0.08<d<1μm)0.2μm filtered ND 0.2μm

（0.08<d<0.7μm)

Radio. Cs suspended particle size

5cm settlement for 16hrs 1056Bq/kg (1μm)Centrifuge (10000rpm,1hr) sediment: 983Bq/kg -Centrifuge (10000rpm,1hr) supernatant: 73 1.2μm

（0.7<d<10μm)0.2μm filtered 67 ND

(No particle of greater than 1nm)

After (H2O2 +Heat) treatmenton Suspension A

Can ionic Cs remain after H2O2 treatment?

13

Column experiment on transport of Cs with organic colloids

• Non-Cs polluted Paddy soil （30-50 cm，Sasu, Iitate, Fukushima）→ Passed through 2 mm mesh screen

0 cm

Surface soil

clay silt sand

19 % 20 % 61 %

• Particle density： 2.66 g/cm3

• Texture：Sandy clay loam

40 cm

70 cm

subsoil

30 cm

50 cm

Soil sample

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1. Percolation of non-Cssolution

2. Displace to Cs containedsuspension

3. After the end of percolationsoil column was separatedand suffered to Cs analysis.

Samplecollector

reservoir

Flow analysis

tensiometer

7 cm

5 cm

4 cm

30 cm

1 cm

5 cm

soil

Use NaI counter to measure 134Cs and137Cs (Wizard 2480, Perkin Elmer)

15

Observation of effluent from bottom of the column

Tap water

Suspension A

Suspension B

16

Visual results agreed radioactive Cs in the effluent

Suspension A SuspensionB

0

0.2

0.4

0.6

0.8

1

0 2 4 6 8 10

ポアボリューム(P.V.)

コロイド結合態 Cs

溶存態 Cs

0

0.2

0.4

0.6

0.8

1

0 2 4 6 8 10

ポアボリューム(P.V.)

相対濃度

Suspension A Particulate（＞1.2μm）

supernatant（＜ 1.2μm）

● Particulate（＞0.2μm）

□ supernatant（＜ 0.2μm）(supernatnt had no radioactive Cs)

120mm 360mm 120mm 240mmWater depth

Suspension B

240mm Water depth

Relative

concentartion

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Radioactive Cs in soil column

0 2000 4000 6000

0-1

1-2

2-3

3-4

4-6

6-8

8-10試料

上端

からの

距離

[cm]

放射性Cs濃度 [Bq/kg]

134 Cs

137 Cs

0 2000 4000 6000

0-1

1-2

2-3

3-4

4-6

6-8

8-10試料

上端

からの

距離

[cm]

放射性Cs濃度 [Bq/kg]

134 Cs

137 Cs

Suspension A Suspension B

Radioactive Cs concentration

[Bq/kg-soil]

Radioactive Cs concentration

[Bq/kg-soil]

Deoth

[cm]

18

Thank you for attention

Acknowledge: Meiji University Recovery Support project, JSPS (#24380130)

19

D=6 nm

Form of Cs and capture

Prussian blue, Iron(III) hexacyanoferrate(II)AIST (Tsukuba)http://www.aist.go.jp/aist_j/new_research/nr20120905/nr20120905.html

＜1nm

0.6 nm

Organic colloid extractedlitter＞80nm

Moldenite (zeolite)http://www9.canet.ne.jp/users/soken/zeolito.html

Clinoptilolite (zeollite) (0.3nm)

Capture ofCs inside thecrystalstructure