| Abstrakt: |
Laboratory synthesized hydroxy‐Al solutions were characterized by nuclear magnetic resonance (NMR) spectroscopy. Solutions ranging in Al concentration from 3.4 × 10−3to 1.0 mol L−1at OH/Al ratios (ñ) of 0, 0.25, 0.50, 0.75, 1.00, 1.25, 1.50, 1.75, 2.25, and 2.50 prepared with base injection rates of 0.6 and 1.2 cm3min−1were investigated. For concentrated solutions (0.5 mol L−1), two polymeric species produced observable resonance peaks, the [AlO4Al12(OH)24(H2O)2]7+polynuclear (i.e., “Al13”) species with a chemical shift (δ) 63‐ppm downfield of the hexaaquaaluminum species, and the dimer Al2(OH)2(H2O)4+8, which displayed a broad resonance ≅ 3‐ppm downfield from the hexaaqua‐Al cation. In solutions of much lower Al concentration (3.4 × 10−2mol L−1), the Al13polynuclear species was observed at ñ>0.25 and its concentration was found to increase linearly as a function of ñ. For ñ= 2.5, the concentration of the Al13polymer decreased at the 1.2 cm3min−1base injection rate; however, this was not the case at the 0.6 cm3min−1neutralization rate where the concentration continued to increase linearly. The data suggest that the distribution of Al species in partially neutralized solutions are acutely sensitive to Al concentration and neutralization rate. |
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