Effect of Li, Fe, and B Addition on the Crystallization Behavior of Sodium Aluminosilicate Glasses as Analogues for Hanf
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Effect of Li, Fe, and B Addition on the Crystallization Behavior of Sodium Aluminosilicate Glasses as Analogues for Hanford High Level Waste Glasses José Marcial1, Mostafa Ahmadzadeh1, John S. McCloy1,2 1
Materials Science and Engineering Program, Washington State University, Pullman, WA
99164, USA 2
School of Mechanical and Materials Engineering, Washington State University, Pullman, WA
99164, USA
ABSTRACT Crystallization of aluminosilicates during the conversion of Hanford high-level waste (HLW) to glass is a function of the composition of the glass-forming melt. In high-sodium, highaluminum waste streams, the crystallization of nepheline (NaAlSiO4) removes chemically durable glass-formers from the melt, leaving behind a residual melt that is enriched in less durable components, such as sodium and boron. We seek to further understand the effect of lithium, boron, and iron addition on the crystallization of model silicate glasses as analogues for the complex waste glass. Boron and iron behave as glass intermediates which allow for crystallization when present in low additions but frustrate crystallization in high additions. In this work, we seek to compare the average structures of quenched and heat treated glasses through Raman spectroscopy, X-ray diffraction, vibrating sample magnetometry, and X-ray pair distribution function analysis. The endmembers of this study are feldspathoid-like (LiAlSiO4, NaAlSiO4, NaBSiO4, and NaFeSiO4), pyroxene-like (LiAlSi2O6, NaAlSi2O6, NaBSi2O6, and NaFeSi2O6), and feldspar-like (LiAlSi3O8, NaAlSi3O8, NaBSi3O8, and NaFeSi3O8). Such a comparison will provide further insight on the complex relationship between the average chemical ordering and topology of glass on crystallization. INTRODUCTION The Hanford site in southeastern Washington state currently stores 177 underground tanks that house over 200,000 m3 of nuclear waste that was generated from the 1940’s through the late 1980’s [1]. This waste will be separated into two categories: low activity waste and high level waste. Low activity waste will constitute approximately 90 mass percent while high level waste (HLW) will constitute over 95 percent of the radioactivity [1]. Waste will be mixed with glassforming additives (e.g., SiO2 and H3BO3) and vitrified in a large-scale melter at the Waste Treatment and Immobilization Plant (WTP) currently under construction. The resulting melt from feed decomposition will be poured into canisters and transferred to a permanent repository. Currently formulations of Hanford HLW glass are particularly high in Na2O, Al2O3, and SiO2. Compositional restrictions must be placed to prevent the crystallization upon cooling along the centerline of the canister, since the crystallization reduces the chemical durability of the final waste form. The crystallization behavior of silicate melts can be markedly influenced by (i) the makeup of the network forming and intermediate compounds (e.g., Al2O3, B2O3, Fe2O3, and SiO2) and (ii) the makeup of the network modifying compounds (e.g., Li2O, and Na2O).
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