Iron adsorption in Cameroon volcanic ashes insights from x-ray absorption spectroscopy

In this study, synchrotron radiation x-ray absorption spectroscopy was used to characterize natural volcanic ash from Mount Cameroon. The latter was employed to remove Fe3+ ions from aqueous solutions, as an option for its application in water treatment. The electronic properties and local structure of Fe adsorbed on the volcanic ash were investigated. The results show that the raw volcanic ashes and those used to adsorb Fe3+ are principally composed of magnetite, Fe(II) sulphate, hematite, and Fe(II) oxide. The volcanic ash materials contain Fe ions coordinated by oxygen atoms with Fe–O bond length provided by magnetite, Fe(II) sulphate, hematite, and Fe(II) oxide. Two types of interactions were suggested: one between oxygen and Fe photo-absorber in the first shell, and the second between another atom of Fe and photo-absorber in the second coordination shell. The adsorption mechanism for Fe3+ removal was attributed to the ion exchange and/or chemisorption processes.