The Immobilization of Radioactively Contaminated Soil in Cementitious Materials

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The Immobilization of Radioactively Contaminated Soil in Cementitious Materials . Shuxin Bai, Shengliang Yang National University of Defense Technology, P.R.China. Introduction/Background. In China, a mass of radioactively contaminated soil is required to be disposed. - PowerPoint PPT Presentation

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  • The Immobilization of Radioactively Contaminated Soil in Cementitious Materials Shuxin Bai, Shengliang YangNational University of Defense Technology, P.R.China

  • Introduction/BackgroundIn 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.

  • Introduction/BackgroundSoil 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.

  • Research MethodologyThe physical and chemical processes occurring during the harden process of soil cement systemincluding: the cementation of cement, soil and other agents, 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, post-treatment of the cementation product.

  • Research MethodologyThe influence of cementitious materials and processes on properties of concrete such as strength, microstructure, porosity, cracking etc. The degradation of the soil cement concrete in water at different conditionsincluding: water penetration and transport in pores of the concrete, dissolution of different components (C-S-H, clay .etc) in the concrete block, the leaching and retention behaviors of different radionuclides (actinides specially).

  • Research Methodology

  • Experimental Techniques and EquipmentTechniques and EquipmentXRD: D-Advance, GermanySEM-EDS: S-4800 SEM, HORIBA EDSICP-AES: IRIS Advantage1000, USAUniversal Materials Testing Machine Mixing DeviceMaterialsvarious cements, cement additives, contaminated soil samples.

  • Research Approach and ResultsDifferent types of cement was adopted to immobilize the contaminated 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 samplesCs+, Sr2+, Ce3+ were added to substitute the 137Cs, 90Sr and 239Puconcentration of each element: ~0.01%(wt)

  • A CaCO3B SiO2C CaSO42H2OD CaAl2Si2O8soil

    oxidesSiO2 CaO SO3 Al2O3 Fe2O3 K2O MgO Na2Owt%40.3 26.5 13.5 9.43 4.49 2.78 1.91 1.05

    Size(mesh) 120wt%17.9 41.9 6.40 22.2 11.6

  • Sample groupCement:SoilPFA%SF%Zeolite%c/wplasticizer%A11:2.015500.400.5A21:2.0151000.450.5A31:2.0151500.500.5B11:2.015050.500.5B21:2.0150100.500.5B31:2.0150150.500.5C11:1.51510100.500.5C21:2.01510100.500.5C31:2.51510100.550.5C41:3.01510100.600.5D11:2.000100.500.5E11:2.0150100.500.0

  • Cemented samplesGood compatibilityHigh soil volume (2.0~2.5:1, or 67~70%wt)Density, but pores visibleAs fabricated wasteform samplesaged wasteform samplesno vibrationCross-section4416cm55cm

  • Research Approach and ResultsThe compressive strength of each group show good results. Aged 28d

    Chart1

    59.5

    49.3

    27.5

    29.9

    29.8

    29

    35.8

    26.5

    24.8

    24.9

    34.1

    23.7

    sample

    compress strength /MPa

    Sheet1

    A159.5

    A249.3

    A327.5

    B129.9

    B229.8

    B329

    C135.8

    C226.5

    C324.8

    C424.9

    D134.1

    E123.7

    Sheet1

    sample

    compress strength /MPa

    Sheet2

    Sheet3

  • Leaching rate resultsGB7023-86Standard:

    Chart3

    0.93370.11310.3814

    0.51570.09430.3623

    0.12970.09430.3814

    0.58570.16030.41

    0.6990.1320.3719

    00.11310.3291

    00.12570.5085

    1.02310.10370.4386

    0.21570.09090.3382

    0.510.13680.3305

    0.67810.54690.4767

    0.38230.23570.9249

    Cs+

    Sr2+

    Ce3+

    sample

    leaching rate (X10 -3 cm/d)

    Sheet1

    Cs+Sr2+Ce3+

    A159.50.93370.11310.3814

    A249.30.51570.09430.3623

    A327.50.12970.09430.3814

    B129.90.58570.16030.41

    B229.80.6990.1320.3719

    B3290.11310.3291

    C135.80.12570.5085

    C226.51.02310.10370.4386

    C324.80.21570.09090.3382

    C424.90.510.13680.3305

    D134.10.67810.54690.4767

    E123.70.38230.23570.9249

    Sheet1

    0

    0

    0

    0

    0

    0

    0

    0

    0

    0

    0

    0

    sample

    compress strength /MPa

    Sheet2

    000

    000

    000

    000

    000

    000

    000

    000

    000

    000

    000

    000

    Cs+

    Sr2+

    Ce3+

    sample

    leaching rate (X10 -3)

    Sheet3

  • Research Approach and ResultsFree water check: no free water observed after aged 7dThermal cycle durability:Loss of compressive strength (-25~15C, 5cycles):
  • Influence of additives on the cement hydraulic processInfluence of soilInfluence of PFAInfluence of silica fumeInfluence of zeolite

  • Influence of soilXRD of hydrated cement and cement-soil grout aged 21dPure OPC cementCement+soil (1:1)AFm decreased for the exist of CaSO42H2O in the soil prevents the formation of AFm from AFt.

  • Influence of PFAXRD of samples aged for 21dXRD of samples aged for 60dNo obvious difference for 21d samples, however for 60d samples phase C remains little amount, indicates reaction between cement and PFA at later period of settingcementCement +PFAcementCement +PFA

  • Influence of PFAThe adding of PFA improves leaching properties:

    Chart1

    0.1320.5469

    0.37190.4767

    15%PFA

    0%PFA

    leaching rate(X10-3cm/d)

    Sheet1

    Sr42Ce42Cs42

    A10.01200.03770.1131A10.04000.03730.3814A10.12530.03710.9337

    A20.01000.03770.0943A20.03800.03730.3623A20.06920.03710.5157

    A30.01000.03770.0943A30.04000.03730.3814A30.01740.03710.1297

    A40.01700.03770.1603A40.04300.03730.4100A40.07860.03710.5857

    A50.01400.03770.1320A50.03900.03730.3719A50.09380.03710.6990

    A60.01200.03770.1131A60.04500.03730.4291A60.03710.0000

    B10.01200.03400.1257B10.04800.03360.5085B10.03340.0000

    B20.01100.03770.1037B20.04600.03730.4386B20.13730.03711.0231

    B30.01000.04310.0825B30.03800.04000.3382B30.03100.03970.2157

    B40.01300.04240.1089B40.03900.04200.3305B40.07700.04180.5100

    C10.05800.03770.5469C10.05000.03730.4767C10.09100.03710.6781

    D10.02500.03770.2357D10.09700.03730.9249D10.05130.03710.3823

    A10.03600.01450.3260A10.06400.01430.5861A10.16420.01421.1752

    A20.01000.01450.0906A20.01000.01430.0916A20.19970.01421.4293

    A50.04400.01450.3985A50.07800.01430.7143A50.20230.01421.4479

    B10.01000.01300.1006B10.02600.01290.2645B10.14600.01281.1617

    B20.01000.01450.0906B20.05200.01430.4762B20.23400.01421.6748

    B30.01300.01550.1099B30.04900.01530.4188B30.07480.01520.4999

    B40.01700.01630.1368B40.06500.01610.5290B40.20700.01601.3169

    C10.01000.01450.0906C10.01000.01430.0916C10.19590.01421.4021

    D10.02500.01450.2264D10.06800.01430.6227D10.22620.01421.6190

    SrCe

    15%PFA0.13200.3719

    0%PFA0.54690.4767

    Sr42Ce42Cs42

    A20.01000.03770.0943A20.03800.03730.0362A20.06920.03710.5157

    A50.01400.03770.1320A50.03900.03730.0372A50.09380.03710.6990

    B30.01000.04310.0825B30.03800.04000.0338B30.03100.03970.2157

    B40.01300.04240.1089B40.03900.04200.0330B40.07700.04180.5100

    A10.01200.03770.1131A10.04000.03730.0381A10.12530.03710.9337

    A30.01000.03770.0943A30.04000.03730.0381A30.01740.03710.1297

    A40.01700.03770.1603A40.04300.03730.0410A40.07860.03710.5857

    A60.01200.03770.1131A60.04500.03730.0429A60.03710.0000

    B10.01200.03400.1257B10.04800.03360.0509B10.03340.0000

    B20.01100.03770.1037B20.04600.03730.0439B20.13730.03711.0231

    C10.05800.03770.5469C10.05000.03730.0477C10.09100.03710.6781

    D10.02500.03770.2357D10.09700.03730.0925D10.05130.03710.3823

    B30.01300.01550.1099B30.04900.01530.4188B30.07480.01520.4999

    B40.01700.01630.1368B40.06500.01610.5290B40.20700.01601.3169

    A10.03600.01450.3260A10.06400.01430.5861A10.16420.01421.1752

    A20.01000.01450.0906A20.01000.01430.0916A20.19970.01421.4293

    A50.04400.01450.3985A50.07800.01430.7143A50.20230.01421.4479

    B10.01000.01300.1006B10.02600.01290.2645B10.14600.01281.1617

    B20.01000.01450.0906B20.05200.01430.4762B20.23400.01421.6748

    C10.01000.01450.0906C10.01000.01430.0916C10.19590.01421.4021

    D10.02500.01450.2264D10.06800.01430.6227D10.22620.01421.6190

    Sheet1

    15%PFA

    0%PFA

    -

    Sheet2

    Sheet3

  • Influence of silica fumecementCement +SFActive SiO2 reacts with Ca(OH)2 to form C-S-HSiO2 + Ca(OH)2 = CaSiO3 + H2OCaSiO3 + nH2O = CaSiO3nH2O XRD of samples aged for 21d

  • Influence of silica fumeThe adding of SF increases the compressive strength of waste formsThe adding of suitable amount of SF decreases the leaching rate of waste forms

    Chart1

    23.65

    59.45

    49.3

    27.5

    SF%

    strengthMPa

    Sheet4

    Sheet1

    0.0023.65

    5.0059.45

    10.0049.30

    15.0027.50

    0.4046.45

    0.4539.30

    0.5027.50

    0.5524.80

    0.6024.90

    0.000.00

    0.0026.50

    5.0029.85

    10.0029.80

    15.0028.95

    1.5035.80

    2.0026.50

    2.5024.80

    3.0024.90

    15%29.80

    34.05

    1%29.80

    23.65

    Sheet1

    23.65

    59.45

    49.3

    27.5

    %

    Mp -

    Sheet2

    0

    0

    0

    0

    0

    Mp -

    Sheet3

    0

    0

    0

    0

    0

    %

    Mp -

    0