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 Ni2+ ions in these suspensions was studied by analysis of the solid products separated from the mother liquor. X-ray powder diffraction indicated that in one sample, a maximum of three crystalline phases were detected: NiFe2O4, alpha-Ni(OH)(2).0.75H(2)O and alpha-FeOOH. The actual phase composition of the samples was very dependent on the experimental conditions. FT-IR spectroscopy indicated the Ni2+ ferritization in the samples obtained at 90 and 120 degrees C, and provided evidence that this process was possible even at 25 degrees C. The Ni2+ ferritization was also monitored by Fe-57 Mossbauer spectroscopy. The relative intensity of the hyperfine magnetic splitting component increased with the aging time at 90 degrees C. The effect of particle size on the shape of these spectra was suggested. The superposition of two central quadrupole doublets was discussed in the sense of the presence of the NiFe2O4 precursor and in some samples of ferrihydrite. The visible and near-infrared diffuse reflectance spectra also gave evidence of Ni2+ ferritization in the samples investigated. The characteristic bands, which supported this conclusion, were interpreted. (C) 1998 Elsevier Science S.A. All rights reserved.