FERRITIZATION OF NI2+ IONS IN MIXED HYDROXIDE SUSPENSIONS

Mixed hydroxide suspensions with a molar ratio of NiO:Fe2O3 = 1:1 were aged at 25, 90 or 120 degrees C for various times. Ferritization of N i2+ ions in these suspensions was studied by analysis of the solid pro ducts separated from the mother liquor. X-ray powder diffraction indic ated that in one sample, a maximum of three crystalline phases were de tected: NiFe2O4, alpha-Ni(OH)(2).0.75H(2)O and alpha-FeOOH. The actual phase composition of the samples was very dependent on the experiment al conditions. FT-IR spectroscopy indicated the Ni2+ ferritization in the samples obtained at 90 and 120 degrees C, and provided evidence th at this process was possible even at 25 degrees C. The Ni2+ ferritizat ion was also monitored by Fe-57 Mossbauer spectroscopy. The relative i ntensity of the hyperfine magnetic splitting component increased with the aging time at 90 degrees C. The effect of particle size on the sha pe of these spectra was suggested. The superposition of two central qu adrupole doublets was discussed in the sense of the presence of the Ni Fe2O4 precursor and in some samples of ferrihydrite. The visible and n ear-infrared diffuse reflectance spectra also gave evidence of Ni2+ fe rritization in the samples investigated. The characteristic bands, whi ch supported this conclusion, were interpreted. (C) 1998 Elsevier Scie nce S.A. All rights reserved.