SPECIATION OF ALUMINUM IN HYDROXYALUMINUM AND HYDROXYALUMINOSILICATE IONS FIXED BY MONTMORILLONITE, USING 27Al-NMR AND ICP-AES

Abstract

We tried to elucidate the chemical species of hydroxyaluminum (HyA) and hydroxyaluminosilicate (HAS) ions intercalated into the Mt focusing on the Al by means of 27 Al-NMR, inductively coupled plasma atomic emission spectroscopy (ICP-AES), differential thermal analysis (DTA), x-ray diffraction (XRD), and fourier-transform infrared (FTIR). Using 27 Al-NMR and ICP-AES, the Al in a Al-OH-Si(OH) 4 mixture was separated into three fractions; Al 13 , Al SYM , and Al NON . The Al 13 and Al SYM were quantitatively determined by 27 Al-NMR at 62.5 and 0 ppm, respectively. The Al NON was defined as the Al which can be determined by ICP-AES but not by 27 Al-NMR. The Al SYM was attributed to electrically-symmetric octahedral Al including monomer (and dimer) HyA ions, and the Al NON was attributed to electrically-asymmetric Al including HAS and/or polymer HyA ions. Among the HAS and HyA solutions prepared, the proportion of Al 13 ion was higher in the smaller Si/Al ratio. The HAS solutions with the Si/Al ratio greater than 0.24 contained no Al 13 ion. As result of adsorption kinetics of Al 13 , Al SYM , Al NON , and orthosilicic acid in three solutions on the montmorillonite (Mt), most of the adsorption reaction occurred within I min., and Al 13 and HAS ions were selectively adsorbed by Mt compared with the Al SYM . The HyA-Mt complex showed a great expansion in the d-spacing compared with Mt, and the d-spacing of the HyA-Mt was 1.64 nm and its peak was broad. On the other hand, the strongest peak of the HAS-Mt was mostly at around 1.80 nm, irrespective of the Si/Al ratios of the HAS ions used. Intercalation of HAS ions may occur completely since the enlargement of the d-spacing was clearly seen by XRD and no specific absorption bands were not seen by FTIR. Most of the thermal characteristics of the Mt would be modified by the intercalated HAS ions with a higher Si/Al ratio greater than 0.05. These results indicate that, upon the intercalation of Mt, the outer surface properties detectable by the FTIR were not modified greatly, while the internal surface structure of the complex detected by XRD and DTA analyses was modified greatly. Al 1 3 ions could not be fixed in the interlayer space of the Mt, and most of the changes was brought by the fixation of HAS ions in the internal space of Mt.