Fe speciation in geopolymers with Si/Al molar ratio of ∼2

The speciation of Fe was studied in metakaolin-based geopolymers to which Fe was added as ferric nitrate solution or freshly precipitated ferric hydroxide. From Mössbauer and near-edge X-ray absorption spectroscopies, coupled with X-ray diffraction and electron microscopy, it was concluded that in as-cured geopolymers the Fe was present in octahedral sites, either as isolated ions in the geopolymer matrix or as oxyhydroxide aggregates which had not reacted with the starting geopolymer components. For material to which iron nitrate was added, heating to 900 °C allowed the formation of nepheline and a glass, both of which contained tetrahedrally coordinated, substituted Fe3+.