Brendler, Vinzenz

Mayordomo, Natalia

Müller, Katharina

Rodríguez, Diana M.

Scheinost, Andreas C.

Schild, Dieter

English

KITopen

Reductive immobilization of 99Tc(VII) by pyrite and marcasiteFPs main part of resulting additional dose in the biosphere:135Cs, 129I, 99Tc, 79Se, 36Cl, 14Cpoorly retained by the naturaland technical materials in the repositoryImproving the level of knowledge about their solubility and retention can, if taken into account in the long-term safety analysis, lead to a significant reduction in uncertainty.D. M. Rodríguez1), N. Mayordomo1), V. Brendler1), A. C. Scheinost1,2), D. Schild3), K. Müller1)Fission products (FPs) in the environment of a repository for  high level radioactive wasteInstitute of Resource Ecology · Department of Surface ProcessesDr. Katharina Müller · k.Mueller@hzdr.de · www.hzdr.de1) Institute of Resource Ecology, Helmholtz-Zentrum Dresden – Rossendorf e.V., Bautzner Landstraße 400, 01328 Dresden, Germany 2) The Rossendorf Beamline (BM20), European Synchrotron Radiation Facility, B.P 200, F-38043 Grenoble Cedex, France3) Institute for Nuclear Waste Disposal, Karlsruhe Institute of Technology, Hermann-von-Helmholtz Platz 1, 76344 Eggenstein-Leopoldshafen, GermanyAccess of waterMobilized FPs02NUK072 02E11607BMobility of contaminants at water-mineral interfacesTool box for comprehensive molecular understandingEnvironmental safety assessment To consider all processes comprehensively Thermodynamic databases need species verificationCharacterization of Fe(II) sulfides20 40 60 800,00,51,0Normalized Intensity / A. U.2q / ° REF pyrite REF marcasite Mixture Pure pyritePure pyrite: BET = 2.0 m2 g-1, pH IEP = 7.9Mixture 60:40 marcasite–pyrite: BET = 5.3 m2 g-1, pH IEP = 7.4Hypothesis Conclusions & Outlook Tc removal by FeS2 minerals is driven by the reduction from Tc(VII) to Tc(IV)  Pyrite shows a higher affinity for Tc than the mixture, suggesting that marcasite inhibits the Tc uptake Different redox functionalities (Fe2+ and S2-) are responsible  pH dependent retention mechanisms on both FeS2Surface-mediated reduction of Tc(VII) to Tc(IV) followed byretention reactions on mineral surfaces TcVIIO4- Almost inert High mobility Hardly soluble, TcO2 Precipitated, sorbed or incorporated 1,2,3,4 Reduced mobility Tc(VII) Tc(IV) Fe2+, S2-Fe3+, SO42+3 4 5 6 7 8 9 10 11204060801003 4 5 6 7 8 9 10 110.000.020.044 5 6 7 8 9 10 11-0.4-0.20.00.20.43 4 5 6 7 8 9 10 116080100% Tc removedpH 1 day 7 days 14 days 21 days 24 days 35 days 42 days[Fe2+] (g L-1)pHTcO4- TcO4-/TcO2 WaterEh (V)pHTcO2% Tc removedpH Water 0.1 M NaClBatch retention experiments of Tc(VII) on pure pyrite 7 … … and on a mixed marcasite-pyrite sample 8-10 -9 -8 -7 -6 -5 -4 -3 -2-7,5-7,0-6,5-6,0-5,5-5,0-4,5-4,04 5 6 7 8 9 10 11-0,4-0,20,00,20,40 10 20 30 40 50204060801003 4 5 6 7 8 9 10 11 12020406080100Log (mol Tcremoved / g)Log ([Tc]in solution)TcO2 (TcO-4/TcO2) Water 0.1 M NaClEh (V)pHTcO-4 Pure pyrite Mix marcasite-pyrite% Tcremovedt (Days) Pure pyriteMix marcasite-pyrite (Water)Mix marcasite-pyrite (0.1 M NaCl)% TcremovedpHTcIV dimers sorption as inner-sphere complexes (pH 6)TcIV incorporation, replacing Fe in octahedral position (pH 10)01010101200 400 600 800 1000 1200 1400 160001FeS2 + Tc pH 6.0HematiteNormalized intensitySynthetic FeS2FeS2 + Tc pH 10.0Raman shift (cm-1)RozenitepH dependent retention mechanisms on pure pyrite 7 The impact of marcasite 8FeIIS2 FeS2 removes Tc quantitatively at 6 < pH ≤ 9 Less retention at high pH for mixed sample Kinetically controlled processes Eh confirms reduction of Tc(VII) to Tc(IV) No dependence on ionic strengthIndication of the role of S2- as reductant in marcasite1 Peretyazhko et al. (2008) GCA; 2 Mayordomo et al. (2020) J. Hazard. Mater.; 3 Mayordomo et al. (2021) Chem. Eng. J.; 4 Schmeide et al. (2021) STOTEN; 5 Yalçıntaş et al. (2016) Dalt. Trans.; 6 Livens, et al. (2004) J. Environ. Radioact., 7 Rodriguez et al. (2020) Environ. Sci. Technol.; 8 Rodriguez et al. (2021) Chemosphere Fe(II) sulphur minerals are ubiquitous minerals and very redox sensitive Mackinawite (FeS) showed excellent Tc immobilization capabilities 5,6 Due to the repository conditions, FeS2 will be formed as pyrite and marcasiteReduced Tc mobility is expected in the near-and far-field of nuclear waste repositories where FeS2 is  abundantFunding acknowledged from Funding acknowledged from21,00 21,05 21,10 21,15 21,20-1011000 ppm Tc pH 10600 ppm Tc pH 10pH 6pH 10pH 10TcSxpH 6TcIVO2 xH2OTcVIIO4-(aq)  Normalized fluorescence Photon energy (keV)600 ppm Tc pH 61000 ppm Tc pH 62 4 6 8 10-500  c(k) k3 k [Å-1]0 1 2 3 4 5 6 7 8-404STcSxTc in magnetitestructure Tc dimers sorbedto magnetiteO  Fourier Transform MagnitudeR+DR (Å) Solely identification of Tc(IV)  Tc is prevalently coordinated to oxygen pH dependent identification of secondary mineral phases Retention slower and less effective pH 10: Identification of Fe(II)-sulfate mineral  Presence of TcSx at all pHs, possibly passivating the surface preventing further Tc reduction2402452502552602650,00,51,0 TcS23d5/2253.8 eV3d3/23d5/2256.5 eVNormalized intensity (A.U.)Binding Energy (eV) Mixture + Tc 1000 ppm pH 10  Mixture + Tc 1000 ppm pH 6TcO22352402452502552602652700,00,51,0TcS23d5/2253.8 eV3d3/23d5/2256.5 eVNormalized intensity / A.U.Binding Energy / eV Pyrite + Tc 1000 ppm pH 10  Pyrite + Tc 1000 ppm pH 6TcO2

Reductive immobilization of ⁹⁹Tc(VII) by pyrite and marcasite

https://publikationen.bibliothek.kit.edu/1000163841/151606194

Reductive immobilization of ⁹⁹Tc(VII) by pyrite and marcasite

Abstract

Similar works

Full text

Available Versions

KITopen