Oxidation states and structural role of iron in sodium iron aluminophosphate glass: A combined study of XAFS experiments and MD simulations

Vitrification has gained global recognition as one of the most mature techniques for solidification of high-level nuclear waste, and borosilicate glass has been widely used in various countries as the base material. However, iron aluminophosphate glass also found advantages in solidify waste forms containing high concentrations of Zr, Mo and rare earth elements. In this work, oxidation states of Fe and its structural role of sodium iron aluminophosphate glass have been investigated using X-ray absorption fine structure spectroscopy experiments and molecular dynamic simulations. Results show that both the Fe²⁺ concentration and the average phosphorus number around Fe increase with the replacement of Na by Fe; whereas, the average oxygen number around Fe decreases. Fe²⁺ ions are mainly four-coordinated, and Fe³⁺ ions are mainly five-coordinated. Moreover, additional Fe content leads to the gradual replacement of Al/P–O–P linkages by Fe²⁺–O–P linkages, resulting in the enhancement of the chemical durability of the glass.