Mössbauer, FT-IR and FE SEM investigation of iron oxides precipitated from FeSO4 solutions

Mössbauer and Fourier transform infrared (FT-IR) spectroscopies and thermal field emission scanning electron microscopy (FE SEM) were used to investigate the precipitation of iron oxides from FeSO4 solutions. The hydrolysis of urea at 90 °C was utilized as a generator of OH− ions needed for the precipitation of iron oxides. The formation of specific iron oxyhydroxide or oxide phase depended on the concentration of FeSO4 and urea, as well as on the rate of oxygenation. In dependence on the experimental conditions different iron oxide phases, such as goethite, hematite and magnetite were found in the precipitates. Mössbauer spectra showed only the formation of substoichiometric magnetite (Fe3-xO4). Significant spectral differences in the RT Mössbauer spectrum of goethite phase were observed, and the spectra showing the presence of this phase could be fitted only taking into account the distribution of hyperfine magnetic fields. FE SEM inspection showed varying sizes and geometrical shapes of goethite particles. Goethite particles were elongated along the crystallographic c-axis.