ADSORPTION, CO-CRYSTALLIZATION AND ION EXCHANGEADSORPTION, CO-CRYSTALLIZATION AND ION EXCHANGEAS MECHANISMS FOR TECHNETIUM AS MECHANISMS FOR TECHNETIUM DISPOSITIONDISPOSITION

IN SEVERAL SAVANNAH RIVER SITE WASTE TANKSIN SEVERAL SAVANNAH RIVER SITE WASTE TANKS

• K.Guerman,K.Guerman, C. Delegard*, D. Hobbs**C. Delegard*, D. Hobbs**• A. Ananiev, N. Budantseva, A. Ananiev, N. Budantseva, • A. Fedoseev, S.Nikitenko, A. Fedoseev, S.Nikitenko, • N. Popova, V. Shilov, N. Popova, V. Shilov, • V. Silin, V. TarasovV. Silin, V. Tarasov

Institute of Physical Chemistry of Russian Academy of SciencesInstitute of Physical Chemistry of Russian Academy of Sciences(Moscow, (Moscow, Leninsky pr.31, Leninsky pr.31, 119991,Russia)119991,Russia)

* - Pacific Northwest National Laboratory, * - Pacific Northwest National Laboratory, (Richland, Washington 99352 U.S.A.)(Richland, Washington 99352 U.S.A.)

**- Savannah River Site, **- Savannah River Site,

Institute of Physical Institute of Physical Chemistry Chemistry

Russian Academy of Russian Academy of SciencesSciences

D epartm entSurface Sci.

250

D epartm entC ollo id Sci.

250 res.

Lab.TPuE

Lab.TU E

Lab.EX

G R O U PEL.C H .

G R O U PR C H &EC

G R O U PTc

Lab.R C H

Lab.IX

Lab.IN J-2

Lab.IN J-1

Lab.R AD -2

Lab.R AD -1

Lab.F ILTR .

Lab.C ata l.

Lab.AN AL.

Lab.SO LID

D epartm entR adiochem istry

350 res

D epartm entPolym er Sci.

300

D epartm entC orrosion Sci.

300

D irection(E lections N ovem b. 2001)

Collaboration with US/DOE (Hanford, Savannah River and other sites) was very important for IPC RAS in 1993-2001

9999Tc concentrations found in Tc concentrations found in various tank sludgesvarious tank sludges at at SRSSRS

Tank Tank NumberNumber

[Tc-99], [Tc-99], mCi/g mCi/g dried dried solidssolids

ReferenceReference

1717 0.4620.462 d'Entremont et d'Entremont et al. 1997al. 1997

20, white 20, white solidssolids

0.340.34 d'Entremont d'Entremont and Hester and Hester 19961996

20, brown 20, brown solidssolids

0.940.94 d'Entremont d'Entremont and Hester and Hester 19961996

4242 0.220.22 Hay 1999Hay 1999

5151 0.210.21 Hay 1999Hay 1999

88 0.220.22 Hay 1999Hay 1999

1111 0.340.34 Hay 1999Hay 1999

The discovery of relatively The discovery of relatively high high 9999Tc concentrations in Tc concentrations in inorganic mineral sludge inorganic mineral sludge heels taken from some heels taken from some tanks at the US-DOE tanks at the US-DOE

Savannah River Site (SRS) Savannah River Site (SRS) has prompted has prompted

investigations of Tc uptake investigations of Tc uptake from alkaline highly active from alkaline highly active

waste (HAW) by solid waste (HAW) by solid adsorbentsadsorbents

The SRS waste volumes (Table 2.4 of "Integrated Database Report - 1993: S.Spent Fuel and Radioactive Waste

Inventories, Projections, and Characteristics,”] Tc-99 quantities (Table 2.11), and

Tc-99 concentrations calculated from these data

Volume, Tc-99, Ci [Tc-99], Volume, Tc-99, Ci [Tc-99], [Tc], 10[Tc], 106 6 KdKd

liters liters Ci/liter Ci/liter g/liter total g/liter total

Liquid 61.4 1.68E+04 2.74E-03 Liquid 61.4 1.68E+04 2.74E-03 0.162 -0.162 -

Sludge 13.9 1.14E+04 8.20E-03 Sludge 13.9 1.14E+04 8.20E-03 0.483 30.483 3

Salt Cake 53.8 2.78E+03 5.17E-04 Salt Cake 53.8 2.78E+03 5.17E-04 0.0305 0.20.0305 0.2

Overall waste 129.1 3.098E+04 2.40E-03 0.141 Overall waste 129.1 3.098E+04 2.40E-03 0.141 - -

Question to be studied : Which components absorb Tc with Kd higher than 3 and are Question to be studied : Which components absorb Tc with Kd higher than 3 and are resistant to leaching?resistant to leaching?

Sludge components as Sludge components as carriers for Tc(VII) and carriers for Tc(VII) and

Tc(IV)Tc(IV)

. SO D IU M O XALAT E .N a 2C 2O 4

. C R YO LIT E .N a 3AlF6

ALU MIN O SILIC AT ESC AN C R IN IT E

SO D ALIT E

W H IT E SO LID S

. PLAT IN U M G R O U P .MET ALS

R h, R u, Pd

MET AL H YD R O XID ES(Fe, C r, Mn)(O )(O H )

B R O W N SO LID S

SOLID SLUDGE COM PONENTS

TiO2 was also tested

Experimental conditions Experimental conditions for precipitation and for precipitation and

leaching tests:leaching tests:

Precipitation tests: Precipitation tests: Wastes are alkalineWastes are alkaline Tc is redox sensitiveTc is redox sensitive Sharp differences in the Sharp differences in the

redox potential within the redox potential within the tanks are observed, tanks are observed,

So, both:So, both: oxidizing [Tc(VII)]oxidizing [Tc(VII)] and reducing [Tc(IV)] and reducing [Tc(IV)] conditions were tested in conditions were tested in

0.1- 5 N NaOH + 0-5 N NaOH.0.1- 5 N NaOH + 0-5 N NaOH.

Leaching modes: Leaching modes: Surface leaching. Surface leaching. Complete dissolution.Complete dissolution.

Leaching agentsLeaching agents all precipitates : 0.1N NaOH all precipitates : 0.1N NaOH aluminosilicates - NaHFaluminosilicates - NaHF22

Na oxalate - 0.1N NaOH, NaNONa oxalate - 0.1N NaOH, NaNO22

FeOOH - 0.1N NaOH, HFeOOH - 0.1N NaOH, H22OO22

MnOOH - 0.1N NaOH, HMnOOH - 0.1N NaOH, H22OO22

TiOTiO22 - 0.1- 3N NaOH - 0.1- 3N NaOHMethods: Liquid scintillation counting (LSC) of solutions, XRD, NMR, IR

Study of Tc uptake with Study of Tc uptake with AluminosilicatesAluminosilicates under oxidizing under oxidizing

conditions at 70-130conditions at 70-130ooCC

TcOTcO44-- is too large is too large

and therefore it is and therefore it is excludedexcluded from the from the

aluminosilicate aluminosilicate structure in both structure in both

cancrinite and cancrinite and sodalitesodalite

Solution Formed solid Kd

10-3-10-5M Tc0.2-5M NaOH

0.5-5 M NaNO3Cancrinite less 1

10-3-10-5M Tc0.2-5M NaOHNaNO3 free

Sodalite less 1

Literature data have demonstrated the possibility of Literature data have demonstrated the possibility of ClOClO44

-- and MnO and MnO44-- co-crystallisaton with aluminosilicates : co-crystallisaton with aluminosilicates :

purple Na8[AlSiO4]6(MnO4)2 (Weller,1999 etc.)

OUR EXPERIMENTS on TcOOUR EXPERIMENTS on TcO44- - (reaction: NaAlO2+Na2SiO3+NaOH)

Case of Aluminosilicates Case of Aluminosilicates formed in concentrated formed in concentrated

Tc(VII) solutionTc(VII) solution [Tc] = 0.2 M[Tc] = 0.2 M in NaNO3 solutions - cancrinite in NaNO3 solutions - cancrinite in NaNO3-free solutions - in NaNO3-free solutions -

sodalitesodalite Although NMR spectrum Although NMR spectrum

presented shift typical for presented shift typical for coordinated Tc(VII) its coordinated Tc(VII) its concentration is very lowconcentration is very low

Dissolution in NaHFDissolution in NaHF22 and LSC and LSC has shown : [Tc] in solid has shown : [Tc] in solid cancrinite was 57 mg/kg ~ 100 cancrinite was 57 mg/kg ~ 100 times less than in initial solution times less than in initial solution

Tc is excluded from the Tc is excluded from the aluminosilicate structurealuminosilicate structure

Fig. 1. NMR-99Tc spectrum of the aluminosilicate containing

57 mg-Tc/kg. Tc spectrum presents evidence for -30 ppm shift

characteristic of coordinated pertechnetate

Study of Tc uptake with Study of Tc uptake with AluminosilicatesAluminosilicates under under reducing reducing conditionsconditions

( (0.2M N0.2M N22HH55Cl, 1M NaNOCl, 1M NaNO33, , T T = 80= 8000С, t = 3 С, t = 3

d)d)

Precipitation ofcancrinite

Leaching conditions:

NaOHM

Tc yield, %

Leaching agent:

T, oC

Leaching yield , Tc, %

3 hour

1 day 10 days

2.0 18.9 1M NaOH 20 0.8 1 3.7

4.0 32 2M NaOH 20 0.8 1.2 2.0

2.0 25.2 0.1M NaOH + 0.25 M H2O2

60 25 26.9 27

2.0 18.9 0.1M NaOH + 0.5 H2O2

18 4 6.9 7

4.0 32 0.1M NaOH + 0.5 H2O2

18 6.5 6.9 11

Under reducing conditions Tc uptake is important Under reducing conditions Tc uptake is important

Tc(IV) in aluminosilicates is resistant to leachingTc(IV) in aluminosilicates is resistant to leaching

Study of Tc(VII) sorption Study of Tc(VII) sorption by crystalline TiOby crystalline TiO22

under oxidizing conditionsunder oxidizing conditions

Tc(VII) was sorbed by Tc(VII) was sorbed by TiOTiO22 from neutral from neutral solution with Ksolution with Kdd = 30 = 30 ml/g. ml/g.

However, the KHowever, the Kdd at at pH=10 was only 3.3 pH=10 was only 3.3 ml/gml/g

No affinity to Tc(VII) No affinity to Tc(VII) was noted for was noted for TiOTiO2 2 at at pH=12 and higherpH=12 and higher ..

Among the minerals tested

for Tc(VII) uptake, high-

density TiO2 was the most efficient

MST and Silicotitanates yet not tested ..?

Study of Tc uptake withStudy of Tc uptake with Na oxalateNa oxalate under under

oxidizing and reducing conditionsoxidizing and reducing conditions

Tc(VII) is excluded from the Na oxalate structure Tc(VII) is excluded from the Na oxalate structure under oxidizing conditions (Kd = 1-2)under oxidizing conditions (Kd = 1-2)

Under reducing conditions Tc(IV) forms a separate Under reducing conditions Tc(IV) forms a separate TcOTcO22*1.6H*1.6H22O phase - no interaction between Tc O phase - no interaction between Tc hydroxide and Na oxalate were detectedhydroxide and Na oxalate were detected

Tc precipitate is not resistant to leaching with 0.1 N Tc precipitate is not resistant to leaching with 0.1 N NaNONaNO22

NaOH + H2C2O4 = Na2C2O4

X-ray diffraction tests : the precipitate is

sodium oxalate Na2C2O4

(PDF#20-1149)

Study of Tc uptake withStudy of Tc uptake with Cryolite NaCryolite Na33AlFAlF66 under under

oxidizing and reducing conditionsoxidizing and reducing conditions

Reduced Tc Reduced Tc ::

17-35% of Tc(IV) as 17-35% of Tc(IV) as TcClTcCl662-2- is co- is co-precipitated with precipitated with cryolite cryolite

NN22HH55NONO33 inhibits co- inhibits co-precipitationprecipitation

Oxidizing conditionsOxidizing conditions: :

Kd is less 1Kd is less 1

Tc(VII) is excluded Tc(VII) is excluded from cryolite from cryolite structurestructure

6F6F--+NaAlO+NaAlO22+Na+Na22COCO33

X-ray diffraction tests : the precipitate is cryolite Na3AlF6

Study of Tc(IV) uptake Study of Tc(IV) uptake with with Cryolite NaCryolite Na33AlFAlF66

under under rreducing conditionseducing conditions

No [NH4F]

initial,M

[Na2CO3] in

final solution, M

[N2H5NO3], in

final solution, M

Tc(IV) uptake,

%

1234589

10

2,02.53.04,06,02,02,02,0

0,60.60,60.60,60,40,80,6

-------

0,1

202326283525170

• Tc(IV) is added as NaTc(IV) is added as Na22TcClTcCl66 to ( to (NHNH44F+NaAlOF+NaAlO22) solution) solution

• No additional reducing agent in exp. No 1-9No additional reducing agent in exp. No 1-9• Leaching test were impossible to quantify relative to real Leaching test were impossible to quantify relative to real cryolite in tanks as complete peptization occurred.cryolite in tanks as complete peptization occurred.

Study of Tc(IV) uptake with Study of Tc(IV) uptake with FeOOH FeOOH under under rreducing conditionseducing conditions

Precipitation test: Leaching test (t=18 oC, d = days):

Leaching yield ,Tc, %NaOH

M

Tc in solidphase, %

Leachingagent: 1 d 10 d 29 d 105d

0.6 97 0.1M NaOH 1.0 9.8 14.9 24

2.0 88.0 1M NaOH 2.9 16.5 40.2 58

4.0 90 2M NaOH 0.8 2 3 8.2

Reducing agent: 0.02M FeSO4, T = 60Reducing agent: 0.02M FeSO4, T = 6000СС, time = 3 h , time = 3 h Precipitate : FeOOH/FePrecipitate : FeOOH/Fe22OO33

ThoughThough TcTc adsorbed adsorbed betterbetter on iron hydroxides from 0.5–2.0 M NaOH on iron hydroxides from 0.5–2.0 M NaOH than from 3.0-4.0 M NaOH,than from 3.0-4.0 M NaOH, the precipitates formed the precipitates formed at lower NaOH at lower NaOH

concentration were more easily leached by the NaOH leachantconcentration were more easily leached by the NaOH leachantTc leaching with H2O2 was 20 % and with Na2S2O8 was70-100% in 100 days

Study of Tc(IV) uptake with Study of Tc(IV) uptake with MnOOH MnOOH under under rreducing conditionseducing conditions

Reaction NaOH + NaReaction NaOH + Na22MnOMnO44+ N+ N22HH55OH= MnOOHOH= MnOOHX-ray diffraction tests : the freshly precipitated solid X-ray diffraction tests : the freshly precipitated solid

was Mnwas Mn22OO3 3 , the aged precipitate was manganite , the aged precipitate was manganite MnOOH MnOOH (PDF#18-805)(PDF#18-805)

Manganese(III) oxides were effective Tc carriers and underwent chemical transformations on ageing that increased leaching resistance

to most agents.

0

2

4

6

8

10

12

0 2 4 6 8 10 12Time. d

Lea

ched

Tc,

%

1) Mn/Al=1/10

2) Mn/Al=1/40

3)Mn/Al=1/10

4) Mn/Al=1/40

MnOOH precipitation MnOOH leaching to 0.1 NaOH (1,3,4) and Na2S2O8(2)

0

15

30

45

60

75

90

0 5 10 15 20 25 30

Time,d

Tc u

ptak

e by

pre

cipi

tate

, %

Mn/Al=1/10

Mn/Al=1/40

What additional work is necessary to What additional work is necessary to clarify results obtained in the clarify results obtained in the

present workpresent work

It is still possible that some polymeric inorganics involving larger ions It is still possible that some polymeric inorganics involving larger ions (like titanium, forming hydroxides, complex titanates and Silicotitanates) (like titanium, forming hydroxides, complex titanates and Silicotitanates) could be better sorbents for TcOcould be better sorbents for TcO44

--, - additional tests of different (Ti?) , - additional tests of different (Ti?) compounds could explain some cases of Tc presence in sludge, and compounds could explain some cases of Tc presence in sludge, and possibly result in efficient inorganic Tc(VII)-sorbent for long-term storage.possibly result in efficient inorganic Tc(VII)-sorbent for long-term storage.

Tests of the Tc/Fe hydroxide co-precipitate formed at 4M NaOH could be Tests of the Tc/Fe hydroxide co-precipitate formed at 4M NaOH could be continued aiming to demonstrate the nature of the precipitate and its continued aiming to demonstrate the nature of the precipitate and its stability domain. EXAFS/XANES, Tc-NMR and stability domain. EXAFS/XANES, Tc-NMR and -resonance spectroscopy -resonance spectroscopy could be useful for Tc speciation under these conditions.could be useful for Tc speciation under these conditions.

Co-precipitation tests could be continued with the transition metal Co-precipitation tests could be continued with the transition metal hydroxide mixtures (Fe/Ti, Mn/Al, Ti/Cr, Ti/Zr and others) as these could hydroxide mixtures (Fe/Ti, Mn/Al, Ti/Cr, Ti/Zr and others) as these could provide higher affinity to reduced technetium, or even Tc(VII) and higher provide higher affinity to reduced technetium, or even Tc(VII) and higher resistance to leaching. Tc speciation experiments in these cases are resistance to leaching. Tc speciation experiments in these cases are desirable.desirable.

Acknowledgements

• This work was supported by the U.S. Department of EnergyThis work was supported by the U.S. Department of Energy Under a contract to the Institute of Physical Chemistry RAS Under a contract to the Institute of Physical Chemistry RAS by the Office of Environmental Management, Efficient by the Office of Environmental Management, Efficient Separations and Processing Cross cutting Program. Separations and Processing Cross cutting Program.

• We recognize the organizational skill of Dr. M. We recognize the organizational skill of Dr. M. Khankhasaev in contract implementation, Liliya Khankhasaev in contract implementation, Liliya Petrachenkova (SAIC), Dr. V. Polyanichko, IPC financial Petrachenkova (SAIC), Dr. V. Polyanichko, IPC financial manager Edouard German and RAS corr.-member A.K. manager Edouard German and RAS corr.-member A.K. Pikaev for administrative assistancePikaev for administrative assistance. .

• We are thankful to Dr.D. Hobbs for his encouraging We are thankful to Dr.D. Hobbs for his encouraging attention to this work, useful discussions and elaboration attention to this work, useful discussions and elaboration of the experimental programof the experimental program