Transcript
Page 1: The Immobilization  of  Radioactively Contaminated Soil in Cementitious Materials

2nd CRM

The Immobilization of Radioactively Contaminated Soil in Cementitious Materials

Shuxin Bai, Shengliang YangNational University of Defense Techn

ology, P.R.China

Page 2: The Immobilization  of  Radioactively Contaminated Soil in Cementitious Materials

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Introduction/Background In China, a mass of radioactively

contaminated soil is required to be disposed.

From the point of effectiveness and economy, cementation is a promising candidate approach to immobilize such kind of waste.

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Introduction/Background Soil in the cement paste may deteriorate

its allover properties. Especially when soil is present in the form

of clump. But if well designed and processed, the

contaminated soil can be mixed with cement and additional agents to form clay cement concrete of good durability.

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Research Methodology The physical and chemical processes occurring du

ring the harden process of soil cement system including: the cementation of cement, soil and other ag

ents, and role of them, interactions of cement and soil, the state of radionuclides in the concrete, etc.

Specific of cementation process for soil: pretreatment of the soil, mixing device and method, pos

t-treatment of the cementation product.

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Research Methodology The influence of cementitious materials and proce

sses on properties of concrete such as strength, microstructure, porosity, cracking etc.

The degradation of the soil cement concrete in water at different conditions including: water penetration and transport in pores of th

e concrete, dissolution of different components (C-S-H, clay .etc) in the concrete block, the leaching and retention behaviors of different radionuclides (actinides specially).

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Research Methodology

Wasterform Preparing

Aging for 28d

Cementing Materials

Pretreating of Soil

Testing Properties

XRD

SEM+EDS

Thermal Cycling

Leaching Behavior

Shocking Properties

Compressive Strength

Other aspects

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Experimental Techniques and Equipment

Techniques and Equipment XRD: D-Advance, Germany SEM-EDS: S-4800 SEM, HORIBA EDS ICP-AES: IRIS Advantage1000, USA Universal Materials Testing Machine Mixing Device

Materials various cements, cement additives, contaminated soil

samples.

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Research Approach and Results Different types of cement was adopted to immobilize the co

ntaminated soil. Ordinary Portland Cement (OPC) is used as the main composition.

Additives such as super-plasticizers, pulverized fly ash (PFA), zeolite, silica fume etc. was introduced to enhance the cement properties.

Substituent elements for radionuclides were added to the soil samples

Cs+, Sr2+, Ce3+ were added to substitute the 137Cs, 90Sr and 239Pu concentration of each element: ~0.01%(wt)

Page 9: The Immobilization  of  Radioactively Contaminated Soil in Cementitious Materials

A — CaCO3

B — SiO2

C — CaSO4·2H2O

D —CaAl2Si2O8

oxides SiO2 CaO SO3 Al2O3 Fe2O3 K2O MgO Na2O

wt(%) 40.3 26.5 13.5 9.43 4.49 2.78 1.91 1.05

Size(mesh) <5 5~20 20~40 40~120 >120

wt(%) 17.9 41.9 6.40 22.2 11.6

soil

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Sample group

Cement:Soil

PFA(%) SF(%) Zeolite(%) c/w plasticizer(%)A1 1:2.0 15 5 0 0.40 0.5A2 1:2.0 15 10 0 0.45 0.5A3 1:2.0 15 15 0 0.50 0.5B1 1:2.0 15 0 5 0.50 0.5B2 1:2.0 15 0 10 0.50 0.5B3 1:2.0 15 0 15 0.50 0.5C1 1:1.5 15 10 10 0.50 0.5C2 1:2.0 15 10 10 0.50 0.5C3 1:2.5 15 10 10 0.55 0.5C4 1:3.0 15 10 10 0.60 0.5D1 1:2.0 0 0 10 0.50 0.5E1 1:2.0 15 0 10 0.50 0.0

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As fabricated wasteform samplesaged wasteform samples

no vibration

Cross-section

4416cm

55cm

Cemented samples Good compatibility High soil volume

(2.0~2.5:1, or 67~70%wt) Density, but pores visible

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Research Approach and Results The compressive strength of each group show good results.

0

10

20

30

40

50

60

70

A1 A2 A3 B1 B2 B3 C1 C2 C3 C4 D1 E1sampl e

comp

ress

str

engt

h /M

Pa

Aged 28d

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Leaching rate results

0

0.2

0.4

0.6

0.8

1

1.2

A1 A2 A3 B1 B2 B3 C1 C2 C3 C4 D1 E1

sample

leac

hing

rate

(X10

-3 cm

/d)

Cs+

Sr2+Ce3+

137 3Cs 4 10 cm / d 90 3Sr 1 10 cm / d 239 5Pu 1 10 cm / d

GB7023-86Standard:

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Research Approach and Results

Free water check: no free water observed after aged 7d Thermal cycle durability:

Loss of compressive strength (-25~15C, 5cycles): <25%

No obvious change after 60 cycles (-40C ~ 40C, quenching in LN2)

No. Before/MPa

After/MPa

Loss %

A3 27.5 25.3 8.0

B3 30.0 25.7 11.2

C3 24.8 19.7 20.4 60 cycles from -40C to 40C

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Influence of additives on the cement hydraulic process

Influence of soil Influence of PFA Influence of silica fume Influence of zeolite

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Influence of soil

XRD of hydrated cement and cement-soil grout aged 21d

Pure OPC cement

Cement+soil (1:1)

AFm decreased for the exist of CaSO42H2O in the soil prevents the formation of AFm from AFt.

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Influence of PFA

XRD of samples aged for 21d XRD of samples aged for 60d

No obvious difference for 21d samples, however for 60d samples phase C remains little amount, indicates reaction between cement and PFA at later period of setting

cement

Cement +PFA

cement

Cement +PFA

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Influence of PFA

0. 1320

0. 3719

0. 54690. 4767

0. 0000

0. 1000

0. 2000

0. 3000

0. 4000

0. 5000

0. 6000

Sr Ce

leac

hing

rat

e(X1

0-3cm

/d) 15%PFA

0%PFA

The adding of PFA improves leaching properties:

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Influence of silica fume

cement

Cement +SF Active SiO2 reacts with Ca(OH)2

to form C-S-H

SiO2 + Ca(OH)2 = CaSiO3 + H2O

CaSiO3 + nH2O = CaSiO3·nH2O

XRD of samples aged for 21d

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0

1020

3040

5060

70

0 2 4 6 8 10 12 14 16SF %( )

stre

ngth

MPa

()

0. 0000

0. 1000

0. 2000

0. 3000

0. 4000

0. 5000

0. 6000

0% 5% 10% 15% 20%SF

leac

hing

rat

e(X1

0-3cm

/d)

SrCe

Influence of silica fume

The adding of SF increases the compressive strength of waste forms

The adding of suitable amount of SF decreases the leaching rate of waste forms

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Influence of zeoliteA — SiO2

B — montolite

0. 000. 100. 200. 300. 400. 500. 600. 700. 800. 901. 00

0% 5% 10% 15% 20%zeol i te

lea

chin

g ra

te(X

10-3

cm/d

)

SrCe The leaching rate decrea

ses with the adding of zeolite

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Influence of other aspects water/cement ratio: plasticizer is necessary Vibration of cemented waste form before setting increase t

he strength and decrease the leaching rate

0. 13200. 2357

0. 3719

0. 9249

0. 000. 100. 200. 300. 400. 500. 600. 700. 800. 901. 00

0. 50 0. 55w/ c

leac

hing

rat

e (X

10-3

cm/d

)

Sr2+Ce3+

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Research results and conclusion

cemented waste forms with high durability and low cost: Soil/cement ratio: 2.0~2.5 Compressive strength: >10MPa Leaching rate of Cs+, Sr2+ <410-3, 110-3 cm/d Thermal cycle durability: the same after 60 freeze

thaw cycles (-40,+40 )℃ Unit cost of immobilization: <50€/t of soil

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Research results and conclusion

the soil cemented in this work which is mainly composed of sand and stone has good compatibility with cement and a high encapsulating ratio can be achieved.

At a ratio of cement/soil =1:2.5 the cementing process is still viable and the properties of the waste form including the strength and leaching rate of Sr2+ and Cs+ are accordant with the requirement of the standards .

The investigation of the hydraulic process of the cemented specimen indicates that the exist of soil has apparent effect on the hydraulic process. The CaSO44H2O in the soil retards the formation of hydraulic product AFm .

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Research results and conclusion The effects of the addition of silica fume, zeolite and PFA on the properties

of the cemented waste forms were studied and the results show that the addition of these additives can improve the properties of the waste forms including enhancing the strength and reducing the leaching rate.

Some other cementation processing aspects such as water/cement ratio and whether the specimen being vibrated or not also have important effects on the properties of the waste form. The water/cement ratio can be reduced by adding super-plasticizer to improve the anti-leaching behavior. The vibration during the cementation process can raise the strength and reduce the leaching rate.

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Further works

Massive waste form process of soil immobilization

Suitable method to test the leaching of 239Pu Leaching behavior and immobilizing

mechanism

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2nd CRM


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