Assessment of Nepheline Precipitation in Nuclear Waste Glass Via Thermochemical Modeling

Effects of Al2O3, B2O3, Na2O, and SiO2 on nepheline formation in borosilicate glasses: chemical and physical correlations

“…The calculated three-dimensional nepheline field was projected on the Na 2 O-Al 2 O 3 -SiO 2 ternary plot and compared with the nepheline field in the boron-free system. The calculated effects of SiO 2 and B 2 O 3 on nepheline formation, similar to those observed, resulted from lowering the activity of Na 2 O in the melt, thus restricting the sodium available to form nepheline [35]. An increase in B 2 O 3 would naturally oppose the agglomeration of silicate groups and lower the Na 2 O activity [28,29] or equivalently Na þ -[AlO 4=2 ] À activity.…”

“…This segregation would account for the enhanced preferential leaching of boron from nepheline containing glass [5]. 6 Thermodynamic modeling of nepheline formation in sodium alumino-borosilicate melts was recently reported by Besmann et al [35]. The calculated three-dimensional nepheline field was projected on the Na 2 O-Al 2 O 3 -SiO 2 ternary plot and compared with the nepheline field in the boron-free system.…”

Nepheline Crystallization in Nuclear Waste Glasses: Progress Toward Acceptance of High‐Alumina Formulations

“…Previously, thermochemical models based on freezing‐point depression of quasi‐crystalline precursors have been proposed to describe the nepheline–spinel liquidus . Associate species models for Na 2 O–B 2 O 3 –SiO 2 ,Na 2 O–Al 2 O 3 –B 2 O 3 –SiO 2 , and Na 2 O–Al 2 O 3 –B 2 O 3 –Cr 2 O 3 –SiO 2 have also been used to generate phase diagrams and liquidus temperature surfaces. The basis for this approach is that the complex oxide solutions can be represented by an ideal solution of end‐member species and intermediate associate species .…”

“…Some recent studies have deliberately varied CaO and B 2 O 3 levels in waste‐glass formulations to attempt to understand these phenomena . However, there is yet no clear explanation for the CaO effect nor is there a quantitative model for the effect of B 2 O 3 , other than some indication from the associate species model that addition of B 2 O 3 suppresses formation of nepheline to lower values of SiO 2 . Additionally, it is very likely that other components influence nepheline precipitation because natural nepheline and related crystals are known to incorporate K, Ca, Fe, Mg, Fe 2+ , Fe 3+ , Mn 2+ , and Ti 4+ …”

Refinement of the Nepheline Discriminator: Results of a Phase Ii Study

“…However, several other components have been shown to impact the propensity for nepheline crystallization, including B 2 O 3 and CaO (potential DWPF frit components), among others. 1,4,[8][9][10] Therefore, the potential exists to further refine the nepheline discriminator to include these components. Refining the nepheline discriminator to include other important components and to reduce conservatism may For each of the two constraining values of the nepheline discriminator, the coordinate-exchange algorithm of JMP Version 6.0.3 14 was used to develop a constrained mixture experimental design over the 12 oxides of Table 2-1 from which the selection of the 12 glass compositions was accomplished.…”