Lanthanum and Neodymium Solubility in Simplified SiO₂–B₂O₃–Na₂O–Al₂O₃–CaO High Level Waste Glass

Abstract

Lanthanum and neodymium incorporation in simplified high level waste glasses has been investigated for SiO 2– B 2 O 3– Na 2 O – Al 2 O 3– CaO compositions quenched from 1200°C, for varying La /( La + Nd ) (atomic) and increasing rare‐earth oxides contents. In this system and beyond the solubility limit, rare‐earths (RE) elements are reported to form apatite phases with the general formula Ca 2 RE 8( SiO 4)6 O 2. In the current study, speciation of these trivalent RE 3+ cations in both amorphous network and crystal phases was determined from X‐ray diffraction, scanning electron microscopy, optical absorption at 10 K, Raman spectroscopy, and electron probe microanalysis. It appeared that RE 2 O 3 solubility was higher for La ‐rich formulations than for Nd ‐rich ones and that an increase in the RE oxide content reduces the connectivity of the network building units through formation of non‐bridging oxygens at the expense of the oxygen bridges. This depolymerization of the glass network did not affect neodymium environment which consisted in silicate tetrahedra. The composition of the apatite crystals was found to be affected by the La /( La + Nd ) of the parent glass and deviation from the ideal composition ( Ca 2 RE 8( SiO 4)6 O 2) occurred in the neodymium end of the system. It thus appears that both RE 2 O 3 solubility and crystal composition are strongly dependent on the type and crystal chemistry of the RE elements.

Effect of V2O5 on crystallization tendency and chemical durability of Mo-bearing aluminoborosilicate glass

“…X-ray diffraction (XRD) data was collected on an X' Pert PRO diffractometer using Cu-K α radiation (λ=1.54187 Å) [31,32]. For XRD measurement, powdered samples with particle size80 μm were used.…”

Impact of rare earth ion size on the phase evolution of MoO3-containing aluminoborosilicate glass-ceramics

“…In complicated starting glass compositions, energy dispersive spectroscopy (EDS) has shown that multiple RE cations, for example, Y 3+ , La 3+ , Ce 3+ /Ce 4+ , Pr 3+ , Nd 3+ , Sm 3+ , along with alkali (for example, Na + ), and alkaline earth ions (for example, Ca 2+ , Sr 2+ ) can simultaneously incorporate into the oxyapatite structure [5]. In comparing La, Nd, and La+Nd in Na-Ca aluminoborosilicate glasses, it was observed that the amount of RE 2 O 3 that could be accommodated in the glass before apatite crystallization was higher for La than Nd, and that overall apatite composition depended on the RE cation present [36].…”

Chemical durability of peraluminous glasses for nuclear waste conditioning

“…¼ ði=ZrÞ altered glass ði=ZrÞ pristine glass (6) A ratio C(i)/C g < 1 in the altered glass means that the altered glass was depleted in element i compared with the pristine glass, whereas a ratio C(i)/C g > 1 indicates that the altered glass was enriched in element i. The transition between the altered glass and the pristine glass was defined as corresponding to a C(i)/C g ratio of 0.5.…”

“…4 Glasses with high rare earth (RE) contents are particularly interesting since REs form a substantial proportion of the waste and are commonly used as non-radioactive surrogates for actinides. [5][6][7] Two composition ranges, both in the SiO 2 -B 2 O 3 -Al 2 O 3 -Na 2 O-CaO-RE 2 O 3 system, have already been explored. [8][9][10][11][12][13][14][15][16] These two domains of composition are defined by the molar oxides R ) with M and M' corresponding to alkaline and alkalineearth elements, respectively.…”