Vitrification of high chrome oxide nuclear waste in iron phosphate glasses

Structural properties of Cr2O3–Fe2O3–P2O5 glasses, Part I

“…However, Huang et al [12] recently reported that a simulated high-level waste containing 4 mass% of Cr 2 O 3 was easily vitrified in an iron phosphate glass at 1150°C and at 1250°C for waste loadings of 55 and 75 mass%, respectively. Even at these high waste loadings, these iron phosphate wasteforms had an excellent chemical durability that met all current standards.…”

A review on immobilization of phosphate containing high level nuclear wastes within glass matrix – Present status and future challenges

“…Previously, Day et al [110] could load simulated waste of ∼32 wt% (against ∼10 wt% in borosilicate glass) for the high sulfate LAW (Hanford), to ∼40 wt% (against ∼20 wt% in borosilicate glass) for the SBW (INEEL), to ∼75 wt% (against ∼15 wt% in borosilicate glass) for the high chrome HLW (Hanford). The better solubility of Cr within Fe phosphate melts is due to its occurrence in +3 state only (instead of Cr 3+ , Cr 4+ , Cr 6+ as found in silicate melts; [37]) which makes it possible to incorporate the cation through breaking P O double bonds [120].Šantić et al [121] investigated the effect of Cr 2 O 3 additions on xCr 2 O 3 -(40 − x)Fe 2 O 3 -60P 2 O 5 (where 0 < x < 10, x is in mol%) pyrophosphate (Q 1 , O/P molar ratio ∼3.5) and noted that replacement of Fe 2 O 3 by Cr 2 O 3 up to 5 mol% does not produce any significant structural changes, however higher loading (e.g. 10 mol%) promote crystallization of chromium orthophosphate (␤-CrPO 4 ) and iron pyrophosphate (Fe 3 (P 2 O 7 ) 2 ) within the matrix.…”

“…Extensive scientific and technological database already exist for the system and the glasses are well accepted by general public. However in reality, borosilicate glasses cannot be considered as a universal wasteform matrix as in many cases HLWs contain elements having poor solubility within it [37,38]. A good example of this is phosphate rich HLWs (P 2 O 5 -HLWs) which have only ∼2-3 wt% (P 2 O 5 ) solubility within borosilicate melts [39].…”

Graphite immobilisation in iron phosphate glass composite materials produced by microwave and conventional sintering routes

“…A survey of the literature on the production of glasses using microwave heating indicated the potential of using iron phosphate glass compositions [22][23][24]. In addition, it is known that the addition of iron improves the chemical durability of phosphate glasses and iron phosphates have been suggested for use in the immobilisation of nuclear wastes [25]. It was also considered that rapid heating using microwave synthesis should minimise the oxidation of the graphite when heating in air.…”