Iron oxidation state and coordination, and hydrolytic durability of sodium-aluminum iron phosphate glasses

The structure of anionic motif, oxidation state and coordination of iron in the series of glasses (mol.%): 40 Na2O, (20-x) Al2O3, x Fe2O3, 40 P2O5 considered as matrices for immobilization of high Fe/Al legacy high level waste were determined by FTIR, Raman and Mössbauer study. The glass network is built from ortho- and pyrophosphate units linked by aluminum-oxygen and iron-oxygen polyhedra. Iron in all the glasses was present as primarily octahedrally coordinated Fe(III) and Fe(II). Fe(III) content in the glasses increased with the increase of the x value and reached ∼74% of total Fe in the glass with x = 15 while reduced to ∼67% of total Fe at x = 20. At the same time the lowest values of cumulative release from glasses into a deionized water for all the elements were found at x = 5. Thus no correlation between the Fe(III)/Fe(II) ratio and cumulative elemental release values was found and iron speciation seems to be not a key factor determining their chemical durability.