The role of iron in the formation of inorganic polymers (geopolymers) from volcanic ash: A 57Fe Mössbauer spectroscopy study

Abstract

The behavior of the iron present in two volcanic ashes was investigated during geopolymer synthesis using sodium hydroxide as the sole alkali activator. XRD, SEM, and room-temperature 57Fe Mössbauer spectroscopy were used to monitor the behavior of the iron during the synthesis reaction. Geopolymers with very good compressive strengths were formed, especially with the finer ash, in which the iron is present in the crystalline minerals ferroan forsterite and augite. Mössbauer spectroscopy identified the ferrous sites in these minerals, plus a ferric site, probably located in an X-ray amorphous phase. The ferroan forsterite in the original ashes did not react with NaOH, but a substantial propo..