Temperature dependence of nickel stabilization in inorganic oxide matrices

Scanning electron microscopy, X-ray diffractometry, X-ray absorption spectroscopy, and other means are used to investigate the effect of thermal treatment temperature, 105-1100 degrees C, on the immobilization of nickel (Ni) by the inorganic oxides of latosol. Ni is more firmly immobilized by the latosol with increasing temperature. Spectral analyses indicate that a shoulder toward the edge-jump appears in the spectra of X-ray absorption near-edge structure for the samples heated at 900 and 1100 degrees C. Moreover, the intensity of the main peak at the edge increases with higher temperature; this information indicates the distortion of the divalent nickel [Ni(II)] environment in the samples heated at 900 and 1100 degrees C. Nevertheless, the distortion is absent from the samples heated at 105 and 500 degrees C. The fact of the distortion of the Ni(II) environment suggests the occurrence of a chemical reaction between the Ni compound and the inorganic matrices of the latosol soil during the heating process at 900 and 1100 degrees C. In addition, the extended X-ray absorption fine structure results correspond well to the X-ray absorption near-edge structure results; the former are supportive of the occurrence of a distorted Ni(II) environment in the samples heated at 900 and 1100 degrees C. The wet-chemistry results show that the samples heated at 900-1100 degrees C leach less Ni than the 105-500 degrees C samples do. The change of the Ni environment is related to the observation that less Ni is leached from the samples heated at 900-1100 degrees C. Furthermore, the pore closing phenomenon is observed only in the 1100 degrees C sample; this phenomenon corresponds with the fact that the 1100 degrees C sample leaches less Ni than the 900 degrees C sample does.