MÖssbauer spectroscopy and x-ray diffraction studies of ferromanganese nodules from central Indian ocean basin

We report room temperature ⁵⁷Fe Mössbauer spectroscopic and powder X-ray diffraction studies carried out on Fe-Mn nodules collected from the Central Indian Ocean Basin, to understand the oxidation state of Iron. Mössbauer spectra of all the nodules exhibit the presence of sharp quadrupole doublet, practically with identical Mössbauer parameters inspite of the difference in Fe-Mn nodules chemical compositions. In all the Fe-Mn nodules samples quadrapole splitting (QS) values are centered around 0.5 mms⁻¹ and Isomer shift (IS) values are centered around 0.3 mms⁻¹. These values are characteristic of iron present either in Fe³⁺ in paramagnetic or super paramagnetic phases. XRD studies suggest that the iron oxide phase/phases in these nodules are microcrystalline in nature. Our study indicates the presence of iron in microcrystalline ferromagnetic state which progressively has been converted to cubic spinel phases when heated at higher temperature.