On the coordination environment of Fe- and Pb-rich solidified industrial waste: An X-ray absorption and Mِssbauer study

The oxidation state and coordination environment of Fe and Pb atoms in a series of homogeneous vitrified Pb- and Fe-rich industrial waste glasses is investigated by means of X-ray absorption fine structure (XAFS) and 57Fe Mössbauer spectroscopies. The waste content in the studied samples varies between 10 and 60 wt.%. The Mössbauer analysis reveals that even though all the glasses contain both Fe3+ and Fe2+ ions, the concentration of Fe2+ decreases with increasing waste content. The XAFS results demonstrate that the structural role of Fe depends on the waste content and the Fe3+ ion occupies increasingly tetrahedral at the expense of octahedral sites as the waste content increases. On the other hand, the Pb2+ coordination environment remains unaffected by the waste content. In order to determine the percentage of FeO6 and FeO4 polyhedra, we propose a mixed model for the analysis of the Fe-K edge extended-XAFS (EXAFS) spectra according to which X% of the Fe atoms occupy tetrahedral sites while the rest (1 − X)% constitute octahedra. The EXAFS results disclose that when the waste content increases from 10 to 40 wt.%, the percentage of FeO6 octahedra decreases from 55 to 13 wt.%. When the waste content exceeds 50 wt.%, Fe is predominantly a glass former. The importance of this finding relies with the fact that stabilized products can be produced using a higher amount of Fe-containing toxic waste and a smaller amount of vitrifying agents.