1. IST-2008 , Port-Elizabeth 7-10 Oct. 2008, South Africa RECENT ADVANCES IN TECHNETIUM ENVIRONMENTALLY FOCUSED STUDIES KONSTANTIN E. GERMAN RUSSIAN ACADEMY OF SCIENCES A.N. FRUMKIN INSTITUTE OF PHYSICAL CHEMISTRY AND ELECTROCHEMISTRY 31/4 Leninsky prospect, Moscow , 119991, RUSSIA, Fax: 7-495- 335-17-78
2. 2008 – The Year of Tc Plan of presentation Tc in the environments – sources, history and modern trends. Tc in acidic and basic HLW. Different methods of Tc HLW treatment (insoluble residues, liquid wastes discharcges, in-tank storage, vitrification, plants decomissioning, transmutation projects ) Chemical species of Tc in waste and environment Physico-chemical aspects of Tc (colloids and nanoparticles)
3. Saying “Tc” here we mean Tc- 99g β-emitter (T½ = 2*105 y) accumulating with ~6% yeild by U, Np or Pu fission = 1kg/t-U Tc concentration in reprocessing solutions ~ 5-80 mg/L Oxydation states: 0, +1, + 2, +2.5, +3, +4 , +5, +6, +7 Insoluble ε-phases = Tc metal Volatile as: Tc2O7, HTcO4 at T>100oC TcO2 and Tc-metal (T>350oC+O2); MTcO4 for M = Na, K, Cs atT>600oC = vitrification? In WATER : Extrimly high migration rate : TcO4-
4. Technetium in the environmentin 1986, NEA_TDB –RARD in 1999 An exceptional issue of “Technetium in the environment” in 1986 although made of independent parts was a complete presentation of all the pre-Chernobyl ideas and results . 13 years later an excellent review of NEA-TDB summed up the chemical thermodynamics of Tc . Time passed being characterized with the controversy of nuclear industry present and future status, drastic for Tc-99 originating mostly as the uranium fission product. The definite stop in nuclear development would fix the further accumulation but now is clearly not the case and we appreciate the authors were continuing efforts in Tc environmentally focused sciences. Several main directions could be drawn out: firstly those dealing with already accumulated Tc [3-5], then, focused on the construction of the migration barriers at the depositories [6-9] and finally examining the Tc in vitrification. The understanding of Tc interaction with microbial extremofils was importantly advanced [10-11]. The review is devoted to these and numerous other results of environmental importance.“Technetium in the Environment” (Proc. CEC-RPP – SERE CEA Seminar - Cadarache, 1984), Eds.: G. Desmet and C. Myttenaere, Elsevier Publishers, L&N-Y. (1986).Rard J.A., Rand M.H., Anderegg G., Wanner H., Chemical thermodynamic of technetium. Eds. Sandino Amalia M., Osthols E. NEA (1999) Elsiever Publ. Amsterdam.
5. Technogenic sources of Tc to theenvironments Accumulation of 99Тс in nuclear industry = 8 ton/yearDischarge sources ofTc: Explsions in atmosphere 180 TBq (Tera=1012) = 490 kg Тс Chernobyl accident = 82 kg NPP 1МBq /year 1000 МВт (электр.), т.е. : В 2000 году все АЭС мира выделили ≈ 350 МБк Тс = 160 г Заводы по переработке обл. топлива ≈ 10% от выбросов ЯТЦ Завод Селафилд в Ирландское море 1952-1986 гг : 770 ТБк Тс = 1200 кг Тс Завод мыс Аг (Франция) 1966 – 86 гг : 70 ТБк Тс = 100 кг Тс Заводы изотопного обогащения U: 90% от выбросов ЯТЦ ≈ 4.1010 Бк Тс/год = 4,5 кг/год Тс (Газодиффузионный завод в ОАК РИДЖ: 1975-82 гг. 5-30 Ки Тс = 0.3 - 2 кг Тс/год, 1982-1989 гг. 0.02 – 0.03 кг Тс/год, 1990 – 0.2 кг, 1992 – 1 кг в связи с началом демонтажа оборудования)
6. Different approaches to handlingthe Tc-radwastes Dilution in natural waters (only two isotopes β− 3H and 99 Tc) (UK, Russia -hystoric) Underground injection HLW, MLW (Tomsk, Krasnoyarsk, Dimitrovgrad) Tank farms storage (military wastes, historic wastes) Vitrification of histric wastes, witrification of raffinates Metal forms New venture forms Separation and storage Separation ant transmutation
7. The 1995-2005 years were Тс marked by severeconfrontation of Norwegian “greens” with Sellafieldauthorities for B205-MAGNOXdischarges into the Irish sea - 180 kg-Тс/year EARPТс-to-sea standard for Sellafield B211 = 10 HLW tanks ( B205 + EARP-B211 + THORP ) 1050 cub. m each :– 1995-2000 - 200 ТBq-Тс 5 tanks for “MAC”– 2000-2003 - 90 ТBk-Тс 2 tanks– sludges– TPPBr - April 23-24 - 2003 2 tanks - THORP 1 – empty in 2003
8. Pollution of the North sea, caused bySellafield, UK) Тс content In the samples collected in 1999 - 2001 water = 0.01- 0.07 Bq/L algae = 510 Bq/kg ( ! ) lobsters = 33 - 42 Бк/кг ( ! ) (acc. to Bellona, Norvege)Risks of refused distribution of Norvege sea-foods
9. Tc discharges in 2002-2005The sum of total-beta activity (excluding tritium) from all nuclear installations has fallen significantly over the past 15 years. Total emissions are dominated by discharges from the nuclear fuel plant at Springfields and to a lesser extent the reprocessing plant at Sellafield. The two installations together contribute approximately 98 % of the overall discharges. The high, but decreasing total-beta discharges from Sellafield are mainly attributable to the radionuclide Technetium-99. The reduction of Sellafield’s total-beta discharges from 2002 to 2005 is a result of the significant reduction in Technetium-99 discharges, due to the vitrification process, since 1994 for oxide fuels and 2003, for magnox fuels. Discharge of Tc-99 to sea (primarily from treatment of stored Magnox wastes) has been reduced between 1994 and 2005.The total beta discharges from Sellafield (2002: 112 TBq, 2003: 83 TBq, 2004: 73 TBq, 2005: 43 TBq) were previously mainly attributable to the radionuclide Technetium-99 (2002: 85 TBq, 2003: 37 TBq, 2004 14 TBq, 2005: 6,7 TBq ), for which abatement technology was installed in 2004. The reduction of Sellafield’s total beta discharges in 2005 is due to the reduction of Technetium-99 (2004 14 TBq, 2005: 6,7 TBq),
10. Tc releases in Europe Mayak Karachay lake VVER 3*10-2 For other European facilities the annual Tc release is negligible
11. Tc behavior during the underground HLW storage Pretreatment : рН + complexones + . . . Ingection into the sandy levels – collectors Migration control ………………………………………………………. . . Tc sorption at the minerals and rocks was studied before Main conclusions Тс(VII) has high migrationGuerman K.E., Kosareva I.M., Peretroukhin V.F., mobilitySavushkina M.K., Egorov N.N., Kudryavtsev E.,Revenko Yu.A. ICEM95. V.1. Cross-cutting Issues Тс(IV) may form both immobileand management of high-level waste and spent fuel.(Eds.: S.Slate, Feizollahi, C.Creer), NY, 1995, p. 713 – 722 . TcO2 and mobile complexes
12. Tc speciation in simulated radioactive wastes conditionnedfor the underground injections (1980-88, 1994, 2000) 10 5 4 3 experiment fit TcO4- - is highly migrative Radiolyses in presence of Fourier Transform Magnitude 0 k 3 χ (k) 2 organic components lead to -5 1 -10 the reduction of Тс(VII) to 0 4 6 8 10 12 14 0 1 2 3 4 5 -1 k (Å ) R + ∆ (Å)EXAFS ROBL_ESRF Tc(V, IV, III) Acetate complexes Тс(V, IV, III) exist but the data are scattered and the structure not systematically studied Acetate complexes of Тс(III) could co-exist withTc(VII) .
13. Russians experience of Tc separation andconversion (decl. avail.for CEA France 1994-1997)Spitsyn V.I., Kuzina A.F., Prokopchuk Yu. Z., Chepurkov G.Ya. , German K.E., Oblova A.A.,Kryuchcov S.V. Preparation of technetium metal by thermal decomposition of tetrabutylammonium pertechnetate in inert gas atmosphere. Report IPCAS, N-P-2907, 1983.Spitsyn V.I., Kuzina A.F., Prokopchuk Yu.Z., Chepurkov G.Ya., German K.E., Oblova A.A., Kryuchcov S.V., Dzekun E.G., Sokhina L.P. Precipitation technology for technetium separation from radioactive wastes. Report Mayak/IPCAS- 1984.Spitsyn V.I., Kuzina A.F., Prokopchuk Yu.Z., Chepurkov G.Ya., German K.E., Oblova A.A., Kryuchcov S.V., Tzarenko A.F., Akopov G.A., Krinitsyn A., Kapitonov V.I., Galkin A.,Maksimenko A., Berezuk N., Mezentsev V.I. Technology of technetium recovery from radwastes.Report Mayak /IPCAS/ Khlopin Radievy.Inst.,1985, N P- 3171. 32 p.Spitsyn V.I., Kuzina A.F., Prokopchuk Yu.Z., Chepurkov G.Ya., Guerman K.E., Oblova A.A.,Kryuchcov S.V., Kapitonov V.I., Mezentsev V.I. Improuvment of anion exchange technetium recovery from radwastes using TBP as eluent. Report Mayak -IPC AS. 1985, N P-3066 , 82 P.German K.E., Kuzina A.F., Spitsyn V.I. Patent: Method of technetium carbide preparation. USSR. Patent No 1258016, 1986.2
14. Russian approach to Tc separation in PUREX included (1980-1986): extraction at the first extraction stage, back extraction at the U-Pu separation stage, anion-exchange separation at QuatPhosBase AER, purification at VP-1AP-AER, denitrification with formic acid or H 2O-SH, precipitation of KTcO4 or R4NTcO4 and its conversion to metal Tc Association MTcO4 Solubility in Density constant in Conversion to metal: M= water at 25°C g/ml water, L/M Search for the Me4N+ 0.135 ± 0.005 1,67 - conditions (Ar-6%H2, gaz 0.096  (2.5 ± 0.7) x 10-2 product evaquation, Et4N+ 1,34 - 1.24 x 10-2 at 20°C (8.7 ±0.2) x 10 -3 Products - volatile and Pr4N+ 7.8 x 10-3  1,26 2,6 ± 0,4 solid, (4.3 ± 0.20) x 10-3 Bu4N+ 4.2 x 10-3 at 20°C 1,17 15 ± 3 Russ.Inorg. Chem-2002 Pent4N+ (7.9 ± 0.2) x 10-4 1,12 27 ± 5 -47-No5 Hex4N+ (7.1 ± 0.5) x 10-5 1,07 40 ± 5 Hept4N+ (8.8 ± 0.8) x 10-6 1,03 52 ± 5p[(C4H9)4N]OH (aqueouse) ↔ [(C4H9)4NOH]p (aqueouse) (8) [(C4H9)4N] (aqueouse) + TcO4 (aqueouse) ↔ [(C4H9)4N]TcO4 (solide) + - (9) [(C4H9)4NOH]p (aqueouse) + TcO4 (aqueouse) ↔ [(C4H9)4NOH]p-1TcO4 (aqueouse) + OH (10) - - HTcO4 ↔ H+ +TcO4- (TcKa) Tc Ka/( TcKa + [H+]) = [TcO4-] /([TcO4-]+ [HTcO4]) = [TcO4-] /[Tc]tot The TcKa was found equl to 4.02 M which is in very good agreement with [ [i]] [i] Ashley K.R., Ball J. R. Solvent extraction and ion exchange, 1994, 12(2), p.239-259.
15. Co-precipitation of Tc(VII) with Bu4NReO4 from 100 ml 1.0 M NaOH, [ TcO4-] = 5*10-4 M, [ Bu4N+] = 0.005 - 0.02 M, reagent = 0.1M NH4ReO4Tc fractionremainedin the solution 0,02M Bu4N 1 0,01M Bu4N 0.005M Bu4N 0.8 0.6 ∆ V= +3% 0.4 0.2 0 100 102 104 106 108 110 Total volume, %
17. Tc under HAW vitrification conditions No stable Tc silicates were found before – but now we know about Tc sodalite although losing in structure stability to cancrinite in presence of common nitrate Pertechnetates are volatile at temp. > 600oC Reduced Tc valence forms – Tc(IV) no interaction with silicates Tc(0) no interaction with silicates Tc separation before HAW vitrification is preferable
18. Methods for Tc separation from alkaline and neutral solutions Not a problem compared to acidic, quite efficient are several methods used in Russia in 1980-85 EXTRACTION ChromatographyKetones : Aceton, QuatPhosBase(KHL-Rad-Methyl-ethyl-ketone,) Inst) +VP-1АP(IPCERAS)ТPPBr/ТPAsBr/CCl4 (= RAILEX) for technologyPolyglicoles HPLC - DIONEX-AS11 (for anallyt separation from MoO4/I/Br/ClO4/TcO4) solidex TPPBr (developed for HLW B205-MAGNOX)- Not easy when Tc species is different from Tc(VII) (Schroeder, 1996 - Hanford: treatment with S2O8 etc.
19. Properties of different reagents for Tc separation by (co-) crystallization or solidex technologyTable 4.1 Aqueous solubilities of technetium salts Тетрафениларсоний бромид Pertechnetate cations Solubility at 25ºC, M (Трибалат, Кузина)Cesium 1.60x10-2 Нитрон (Кузина)Thallium 3.1x10-3Tetrapropylammonium (8.7± 0.2)x10-3 Тетрафенилфосфоний бромид (BNFL) (совместимы сTetrabutylammonium (4.3 ±0.2)x10-3 фосфатными стеклами) 4.2x10-3 at 20° C -4 Тетраалкиламмоний бромид /Tetrapentylammonium (7.9 ±0.2)x10 перренат (осадки совместимы сTetrahexylammonium (7.1 ±0.5)x10-5 боратными стеклами, методTetraheptylammonium (8.8 ±0.8)x10-6 опробован в 1982-85 совм. с ПОTriphenylguanidinium (3.9 ±0.3)x10-3 Маяк, в 1995-97 определеныTetraphenylarsonium (4.0 ±0.2)x10-4 оптимальные осадители, которые рекомендованы КАЭ Франции и ДЭ США) Some of these regents were also used for •Tc-Ion-selective electrode construction •Fiber sorbents production
20. 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 Isolation Valve CappedTank Equipment Risers (typ) Service Line (e.g. steam, air)(e.g. slurry pump) Grout fill Formwork 2000# grout (typ) Underground line (valve closed) Diversion Box CLSM Underground line (line capped)Reducing Grout SRS TYPE IV HIGH LEVEL WASTE TANK Volume, Tc-99, Ci [Tc-99], [Tc], 10 6 Kd liters Ci/liter g/liter total Liquid 61.4 1.68E+04 2.74E-03 0.162 - Sludge 13.9 1.14E+04 8.20E-03 0.483 3 Salt Cake 53.8 2.78E+03 5.17E-04 0.0305 0.2 Overall waste 129.1 3.098E+04 2.40E-03 0.141 - Question to be answered : Which components absorb Tc with Kd higher than 3 and are resistant to leaching?
21. Tc concentrations found in 99 various tank sludges at SRS [Tc-99],The discovery of relatively Tank mCi/g dried Reference high 99 Tc concentrations Number solids in inorganic mineral 17 0.462 dEntremont et sludge heels taken from al. 1997 some tanks at the US- 20, white 0.34 dEntremont andDOE Savannah River Site solids Hester 1996 (SRS) has prompted 20, brown 0.94 dEntremont and investigations of Tc solids Hester 1996 uptake from alkaline 42 0.22 Hay 1999highly active waste (HAW) 51 0.21 Hay 1999 by solid adsorbents 8 0.22 Hay 1999 11 0.34 Hay 1999
22. 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 2 C 2 O 4 TiO2 was also tested
23. 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
24. 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
25. 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
26. 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 was the most Silicotitanates yet not efficient
27. Study of Tc uptake with Na oxalate under oxidizing and reducing conditionsNaOH + H2C2O4 = Na2C2O4X-ray diffraction tests :the precipitate issodium 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
28. Study of Tc uptake with Cryolite Na3AlF6 under oxidizing and reducing conditions6F-+NaAlO2+Na2CO3X-ray diffraction tests :the precipitate is cryolite Na 3 AlF 6 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
29. 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 Na 2 TcCl 6 to ( NH4F+NaAlO2)solution• No additional reducing agent in exp. No 1-9• Leaching test were impossible to quantify
30. 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
31. 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 andunderwent chemical transformations on ageing that increasedleaching resistance to most agents.
32. Boehmite sorbs perrhenate and pertechnetate By Peng-Chu Zhang*, James L. Krumhansl and Patrick V. Brady Sandia National Laboratories, Albuquerque, USA Radiochim. Acta 88, 3692373 (2000)(a) Al(OH)3 - Aluminum hydroxide - gibbsite ;(b) Boehmite [AlO(OH)] -aluminum oxyhydroxide(c) Al2O3 aluminum oxide - corundBoehmite and Al-oxyhydroxide gels sorb ReO4 a non-radioactive analogue of TcO4 from NaNO3 solutions.Sorption appears to be substantially electrostatic (though there appears to be a specific preference for ReO4 over NO3 and is most effective at pH , 8. Measured Kd’s lie between 5 and 105 ml g-1, depending on the solid, pH, and ionic strength. ReO4 and TcO4 are both partially removed from high pH Hanford-type acid waste simulants upon neutralization and formation of Al-rich sludges. It was proposed that sequestration of Tc by boehmite limits dissolved Tc levels in the near and sub-surface environment and for that purpose boehmite might be relied on as a backfill, or reactive barrier, to limit environmental transport of Tc.How Mo-Tc generators could do work being made of Al oxide - oxyhydroxide ???
33. Tc(VII) + S2- Kinetics of the reaction of pertechnetate with sulfide in 0.3M Na S solution at 22oC 2 1.0 0.9 0.8 0.7Convertion degree 0.6 0.5 [Tc], *104M 0.4 Tc2.66 0.3 Tc1.9 Tc1.52 0.2 Tc1.14 Tc0.57 0.1 0.0 0 2 4 6 8 10 12 14 16 18 20 22 24 Time, min
34. Separation of Tc2S7 colloides from Na2S solution byMicrofilterfuge (RAININ Instr. Co) with ultrafiltration membranes - 30000 NMWL Tc2S7 ultrafiltration [Na2S] Formation of colloides Tc2S7 0.0007 0.46M is complète in 50 hours 0.0006 0.0005 0.33M under these conditions 0.2M C(Tc), M/L 0.0004 0.13M 0.0003 0.0002 0.066M [Tc] in the solutions at 0.0001 0.033M times from 50 to 150 hours 0.02M 0 0 25 50 75 100 125 150 175 200 corresponds to true TIME, H solubility of Tc2S7 Solubility Tc2S7 in Na2S solutions 0.00035 0.0003 C(Tc) = -9E-05Ln[Na2S] - 2E-05 0.00025 R2 = 0.9917C(Tc), M/L 0.0002 0.00015 0.0001 0.00005 0 0 0.1 0.2 0.3 0.4 0.5 [Na2S], M/L
35. The reduction of Tc(VII) to Tc(V,IV,III ) by abiotic and biotic processesThe reduction of Tc(VII) to Tc(IV) by abiotic and biotic processes has recentlybeen the subject of extensive studies because it has a significant effect onthe mobility of technetium in waste streams, vadose zones, sediments, andgroundwater. These reaction processes are the basis for certainremediationtechnologies such as permeable barriers composed of zero-valent iron particles (i.e., as metallic iron) or sodium-dithionite reduced soils,which are being tested for immobilization of groundwater contaminants.
36. Microbial reduction of Tc(VII) Microbial reduction of Tc(VII) has been suggested as a potential mechanism for removing technetium from contaminated groundwaters and waste streams (e.g., Lovley 1993, 1995, Lyalikova,German et all. 1994). Certain dissimilatory metal reducing bacteria and sulfate reducing bacteria have been determined to be capable of coupling the oxidation of organic carbon or hydrogen to the reduction of Tc(VII) to Tc(IV) (Lyakikova,German,Khizhnyak Peretrukhin 1994 , 1998, Gavrilov –German 2007 and Lloyd and Macaskie 1996; Lloyd et al. 1997, 1998, 1999, 2000a,b; Wildung et al. 2000; Fredrickson et al. 2000).