Aluminophosphate Glasses with High Sulfate Content
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ALUMINOPHOSPHATE GLASSES WITH HIGH SULFATE CONTENT SERGEY V. STEFANOVSKY*, IGOR A. IVANOV,** AND ANATOLII N. GULIN** *State Corp. ((RADON*, 7 Rostovskii per., 2/14, 119121 Moscow, Russia "**Institute of Technology, Moskovskii prosp., 26, 198013 St.-Petersburg, Russia ABSTRACT To immobilize a high sulfate radioactive wastes a system Na2O-A12 0 3-P2O5 -SO3 has been chosen as one where glasses have a relatively low melting points and good chemical durability. Glasses within partial system 44 Na20, 20 A120 3.(36-x) P205, x SQ3 have been prepared at 1000 °C. A possibility of assimilation up to 12 mole % of SO3 has been established. The basic properties of sulfate-containing glasses as density, microhardness, thermal expansion coefficient, transformation and deformation temperatures, viscosity, electric resistivity, leach rate of ions and diffusion coefficients of 22Na, "5S, 9°Sr and 131Cs have been measured. Glass structure by infrared and EPR spectroscopies has been investigated. INTRODUCTION Among the radioactive wastes there are wastes with high sulfate content (BWR, institutional wastes, acid digestion residues etc.) hardly incorporated in borosilicate glass. Various methods have been proposed to solve this problem, for example, preliminary separation of sulfates by sedimentation as calcium or barium sulfate [1], decomposition of sulfated by reducing agents [2], application of lead- or vanadia-doped borosilicate glasses [3] are able to dissolve an elevated quantities of sulfates, production of glass composites by active agitation of phase separated sulfate-borosilicate melt [4] as well as application of phosphate based glasses [5]. The first four modes require an additional operation steps or make a vitrification process more expensive. Moreover a long-term stability of glass composites as well as metastable phase separated glasses
have not been proven correctly. Sulfate-phosphate glasses have a relatively low chemical durability. However, an addition of polyvalent cations to this glass has been proved to be resulted in the increase of chemical durability [6]. It should be noted, that lead-iron phosphate glasses with excellent chemical durability are well-known [7]. The most convenient additive to phosphate glass leading to a strengthening of its strucrural network is alumina. A glasses in system Na 2O-AI 20 3-P20 5 have been study in details [8-10]. A vitrification process of sodium and sodium-aluminium wastes with aluminophosphate and phosphate additives respectively and properties of prepared glasses have been investigated as well [11-13]. The glass formation and structure of glasses in system Na20-P 2O5 -SO3 was investigated early by infra-red (IR) and EPR spectroscopies [14-17]. In this work the results of investigation of the structure and the properties of glasses in Na2O-A120 3 -P2O5-SO3 system are represented. Some preliminary data were reported in [18]. EXPERIMENTAL The glasses in series 44 Na 2O, 20A120 3, (36-x)P 205, xSO 3 (in mole %) and glasses where 5 mole % of Al20 3 were substituted for either CaO
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