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

Abstract The structure of anionic motif, oxidation state and coordination of iron in the series of glasses (mol.%): 40 Na 2 O, (20- x ) Al 2 O 3 , x Fe 2 O 3 , 40 P 2 O 5 considered as matrices for immobilization of high Fe/Al legacy high level waste were determined by FTIR, Raman and Mossbauer 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.