ADSORPTION, CO-CRYSTALLIZATION AND ION EXCHANGE AS MECHANISMS FOR TECHNETIUM DISPOSITION IN SEVERAL SAVANNAH RIVER SITE WASTE TANKS • K.Guerman, C. Delegard*, D. Hobbs** • A. Ananiev, N. Budantseva, • A. Fedoseev, S.Nikitenko, • N. Popova, V. Shilov, • V. Silin, V. TarasovInstitute of Physical Chemistry of Russian Academy of Sciences (Moscow, Leninsky pr.31, 119991,Russia) * - Pacific Northwest National Laboratory, (Richland, Washington 99352 U.S.A.) **- Savannah River Site,
Institute of Physical Chemistry Russian Academy of Sciences D ir e c t io n ( E le c t io n s N o v e m b . 2 0 0 1 ) D e p a rtm e n t D e p a rtm e n t D e p a rtm e n t D e p a rtm e n t D e p a rtm e n t S u r f a c e S c i. C o llo id S c i. R a d io c h e m is t r y P o ly m e r S c i. C o r r o s io n S c i. 250 2 5 0 re s . 3 5 0 re s 300 300Lab. Lab. Lab. Lab. Lab. Lab. Lab. Lab.TUE EX RCH IX IN J - 1 R A D -1 C a t a l. S O L IDLab. G RO UP G RO UP G RO UP Lab. Lab. Lab. Lab.TP uE E L .C H . RCH&EC Tc IN J - 2 R A D -2 F IL T R . ANAL. Collaboration with US/DOE (Hanford, Savannah River and other sites) was very important for IPC RAS in 1993-2001
Tc concentrations found in 99 various tank sludges at SRS [Tc-99],The discovery of relatively high Tank mCi/g dried Reference 99 Tc concentrations in Number solidsinorganic mineral sludge heels 17 0.462 dEntremont et taken from some tanks at the al. 1997US-DOE Savannah River Site 20, white 0.34 dEntremont and (SRS) has prompted solids Hester 1996 investigations of Tc uptake 20, brown 0.94 dEntremont and from alkaline highly active solids Hester 1996 waste (HAW) by solid 42 0.22 Hay 1999 adsorbents 51 0.21 Hay 1999 8 0.22 Hay 1999 11 0.34 Hay 1999
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], [Tc], 106 Kd liters Ci/liter g/liter totalLiquid 61.4 1.68E+04 2.74E-03 0.162 -Sludge 13.9 1.14E+04 8.20E-03 0.483 3Salt Cake 53.8 2.78E+03 5.17E-04 0.0305 0.2Overall 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 resistant to leaching?
Sludge components as carriers for Tc(VII) and Tc(IV) S O L ID S L U D G E C O M P O N E N T S W H IT E S O L ID S B R O W N S O L ID S A L U M IN O S IL IC A T E S M E T A L H Y D R O X ID E S C A N C R IN IT E (F e , C r, M n )(O )(O H ) S O D A L IT E . C R Y O L IT E . . P L A T IN U M G R O U P . N a 3 A lF 6 M E T A L S R h, R u, P d . S O D IU M O X A L A T E . N a 2C 2O 4 TiO2 was also tested
Experimental conditions for precipitation and leaching tests: Precipitation tests: Leaching modes: Wastes are alkaline Surface leaching. Tc is redox sensitive Complete dissolution. Sharp differences in the Leaching agents redox potential within the all precipitates : 0.1N NaOH tanks are observed, aluminosilicates - NaHF2 So, both: oxidizing [Tc(VII)] Na oxalate - 0.1N NaOH, NaNO2 and reducing [Tc(IV)] FeOOH - 0.1N NaOH, H2O2 conditions were tested in MnOOH - 0.1N NaOH, H2O2 0.1- 5 N NaOH + 0-5 N NaOH. TiO2 - 0.1- 3N NaOH Methods: Liquid scintillation counting (LSC) of solutions, XRD, NMR, IR
Study of Tc uptake with Aluminosilicates under oxidizing conditions at 70-130oC Literature data have demonstrated the possibility ofClO4- and MnO4- co-crystallisaton with aluminosilicates :purple Na8[AlSiO4]6(MnO4)2 (Weller,1999 etc.)OUR EXPERIMENTS on TcO4- (reaction: NaAlO2+Na2SiO3+NaOH) Solution Formed solid Kd TcO4- is too large 10-3-10-5M Tc and therefore it is 0.2-5M NaOH Cancrinite less 10.5-5 M NaNO3 excluded from the aluminosilicate 10-3-10-5M Tc structure in both 0.2-5M NaOH Sodalite less 1 NaNO3 free cancrinite and sodalite
Case of Aluminosilicates formed in concentrated Tc(VII) solution [Tc] = 0.2 M Fig. 1. NMR-99Tc spectrum of the aluminosilicate containing in NaNO3 solutions - cancrinite 57 mg-Tc/kg. Tc spectrum presents evidence for -30 ppm shift characteristic of coordinated pertechnetate in NaNO3-free solutions - sodalite Although NMR spectrum presented shift typical for coordinated Tc(VII) its concentration is very low Dissolution in NaHF2 and LSC has shown : [Tc] in solid cancrinite was 57 mg/kg ~ 100 times less than in initial solution Tc is excluded from the aluminosilicate structure
Study of Tc uptake with Aluminosilicates under reducing conditions (0.2M N2H5Cl, 1M NaNO3, T = 800С, t = 3 d) Precipitation of Leaching conditions: cancrinite↓ Leaching T, Leaching yield , Tc, %NaOH Tc yield, agent: o C 3 1 day 10 days M % hour 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 + 60 25 26.9 27 0.25 M H2O2 2.0 18.9 0.1M NaOH + 18 4 6.9 7 0.5 H2O2 4.0 32 0.1M NaOH + 18 6.5 6.9 11 0.5 H2O2Under reducing conditions Tc uptake is importantTc(IV) in aluminosilicates is resistant to leaching
Study of Tc(VII) sorption by crystalline TiO2 under oxidizing conditions Tc(VII) was sorbed by TiO2 from neutral solution with Kd = 30 ml/g. However, the Kd at pH=10 was only 3.3 ml/g Among the No affinity to Tc(VII) was minerals tested for noted for TiO2 at pH=12 Tc(VII) uptake, and higher . high-density TiO2 MST and Silicotitanates was the most yet not tested ..? efficient
Study of Tc uptake with Na oxalate under oxidizing and reducing conditionsNaOH + H2C2O4 = Na2C2O4 X-ray diffraction tests : the precipitate is sodium oxalate Na2C2O4 (PDF#20-1149) Tc(VII) is excluded from the Na oxalate structure under oxidizing conditions (Kd = 1-2) Under reducing conditions Tc(IV) forms a separate TcO2*1.6H2O phase - no interaction between Tc hydroxide and Na oxalate were detected Tc precipitate is not resistant to leaching with 0.1 N NaNO2
Study of Tc uptake with Cryolite Na3AlF6 under oxidizing and reducing conditions 6F-+NaAlO2+Na2CO3 X-ray diffraction tests : the precipitate is cryolite Na3AlF6 Reduced Tc : Oxidizing conditions: 17-35% of Tc(IV) as TcCl62- is co- Kd is less 1 precipitated with cryolite Tc(VII) is excluded N2H5NO3 inhibits co- from cryolite structure precipitation
Study of Tc(IV) uptake with Cryolite Na3AlF6 under reducing conditions [NH4F] [Na2CO3] in [N2H5NO3], in Tc(IV) No initial, final solution, final solution, uptake, M M M % 1 2,0 0,6 - 20 2 2.5 0.6 - 23 3 3.0 0,6 - 26 4 4,0 0.6 - 28 5 6,0 0,6 - 35 8 2,0 0,4 - 25 9 2,0 0,8 - 17 10 2,0 0,6 0,1 0• Tc(IV) is added as Na2TcCl6 to (NH4F+NaAlO2) solution• No additional reducing agent in exp. No 1-9• Leaching test were impossible to quantify relative toreal cryolite in tanks as complete peptization occurred.
Study of Tc(IV) uptake with FeOOH under reducing conditions Reducing agent: 0.02M FeSO4, T = 600С, time = 3 h Precipitate : FeOOH/Fe2O3 Precipitation test: Leaching test (t=18 oC, d = days): NaOH Tc in solid Leaching Leaching yield ,Tc, % M phase, % agent: 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 Though Tc adsorbed better on iron hydroxides from 0.5–2.0 M NaOH than from 3.0-4.0 M NaOH, the precipitates formed at lower NaOH concentration 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 withMnOOH under reducing conditions Reaction NaOH + Na2MnO4+ N2H5OH= MnOOH X-ray diffraction tests : the freshly precipitated solid was Mn2O3 , the aged precipitate was manganite MnOOH (PDF#18-805) MnOOH precipitation MnOOH leaching to 0.1 NaOH (1,3,4) and Na2S2O8(2) 12 1) Mn/Al=1/10 90 2) Mn/Al=1/40 10 3)Mn/Al=1/10 75 Tc uptake by precipitate, % 8 4) Mn/Al=1/40 Leached Tc, % 60 Mn/Al=1/10 6 45 30 Mn/Al=1/40 4 15 2 0 0 0 5 10 15 20 25 30 0 2 4 6 8 10 12 Time,d Time. d Manganese(III) oxides were effective Tc carriers and underwentchemical transformations on ageing that increased leaching resistanceto most agents.
What additional work is necessary to clarify results obtained in the present work It is still possible that some polymeric inorganics involving larger ions (like titanium, forming hydroxides, complex titanates and Silicotitanates) could be better sorbents for TcO4-, - additional tests of different (Ti?) compounds could explain some cases of Tc presence in sludge, and 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 continued aiming to demonstrate the nature of the precipitate and its stability domain. EXAFS/XANES, Tc-NMR and γ -resonance spectroscopy could be useful for Tc speciation under these conditions. 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 provide higher affinity to reduced technetium, or even Tc(VII) and higher resistance to leaching. Tc speciation experiments in these cases are desirable.
Acknowledgements• This work was supported by the U.S. Department of Energy Under a contract to the Institute of Physical Chemistry RAS by the Office of Environmental Management, Efficient Separations and Processing Cross cutting Program.• We recognize the organizational skill of Dr. M. Khankhasaev in contract implementation, Liliya Petrachenkova (SAIC), Dr. V. Polyanichko, IPC financial manager Edouard German and RAS corr.- member A.K. Pikaev for administrative assistance.• We are thankful to Dr.D. Hobbs for his encouraging attention to this work, useful discussions and elaboration of the experimental program