Crystalline Titanate Ceramic for Immobilization of Tc-99
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Crystalline Titanate Ceramic for Immobilization of Tc-99 Yulia I. Korneyko1, Sergey N. Britvin2,3, Boris E. Burakov1, Andriy Lotnyk4, Lorenz Kienle4, Wulf Depmeier5 and Sergey V. Krivovichev2 1 V.G. Khlopin Radium Institute, 28, 2-nd Murinskiy Ave., St. Petersburg, 194021, Russia 2 Department of Crystallography, Geological Faculty, St. Petersburg State University, Universitetskaya Nab. 7/9, 199034 St. Petersburg, Russia 3 Nanomaterials Research Center, Kola Science Center RAN, Fersman Str. 20, 184200 Apatity, Murmansk Region, Russia 4 Institute for Material Science, Synthesis and Real Structure, University Kiel, Kaiserstr. 2, 24143 Kiel, Germany 5 Institute for Geosciences, University Kiel, Olshausenstr. 40, 24118 Kiel, Germany ABSTRACT Technetium-99 is considered as one of the most dangerous nuclear environmental pollutants due to its long half-life (210,000 y.) and high mobility in aqueous solutions under oxidizing conditions. Development of sorbents, which are capable of irreversible uptake of Tc and further direct conversion into durable ceramic waste forms, is an important field of research. Titanate ceramic doped with up to 10 wt. % Tc was successfully synthesized using Layered Hydrazinium Titanate, LHT-9 (PCT/EP2010/001864) as starting precursor. LHT-9 is a new advanced compound of general formula (N2H5)1/2Ti1.87O4xH2O containing 6-7 wt. % of hydrazine chemically incorporated into a TiO2-based matrix. It was demonstrated that LHT-9 (5g/l) can reductively adsorb up to 90.2 wt. % of Tc from aqueous solutions containing 0.5g Tc/l. The obtained adsorption products can be easily converted into stable titanate ceramic by one-step sintering in argon atmosphere at 1200°C. Phase and chemical composition of synthesized Tcdoped ceramic are discussed. INTRODUCTION Technetium-99 is one of the most difficult components of radioactive wastes to treat with. One of the stable valence states of Tc is (7+), which occurs in aqueous solutions in the anion form of (TcO4)-. All salts of Tc7+ such as KTcO4, NH4TcO4 etc., and oxide Tc2O7 are soluble in water. All solid forms of Tc7+ are likely to volatilize under oxidizing conditions at temperatures of 300°C and higher [1]. Another stable Tc valence state is (4+), for example, in TcO2. But in general, under oxidizing conditions Tc4+ is less stable than Tc7+. Interaction of TcO2 with air at ambient conditions causes formation of Tc2O7. Technetium and titanium have similar ionic radii [2]. Therefore durable titanate host phases are prospective for technetium immobilization. Synthesis of Tc-doped titanate ceramic SYNROC was reported [3-5]. These samples contained 2-3 wt. % Tc in the forms of metallic alloy and oxide phases such as perovskite, Ca(Ti,Tc)O3, and rutile, (Ti,Tc)O2. Another host phase suggested for Tc immobilization is Mg-titanate spinel, Mg2(Ti,Tc)O4 [6-8].
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Some chemical features of Tc are similar to those of Mn. It allows synthesizing Tc-Mnbearing crystalline durable phases. In this case Mn is considered as chemical element which provides full Tc co-precipitation fr
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