Effect of thermal treatment on the formation and transformation of Keggin Al-13 and Al-30 species in hydrolytic polymeric aluminum solutions

摘要

The effect of thermal treatment on the formation and transformation of Al-13 and Al-30 species in highly concentrated hydrolytic polymeric At solutions (HPA) (0.2-1.0 mol L-1) were studied quantitatively using high-field Al-27 nuclear magnetic resonance (NMR) and time-developed Al-Ferron complex colorimetry. The results indicate that the metastable Al-13 species in HPA tends to polymerize and transform into Al-30 and other high polymers upon thermal treatment. The polymerization and transformation are speed up by heating at high temperature. Al-13 content in HPA decreases upon thermal treatment, and Al-30 content increases. Al-13 does not convert to Al-30 quantitatively due to its aggregation and acidic dissociation reactions. Al-13 species is a dominant nanosized Al species in freshly prepared HPA solutions, and its content reaches above 80.0% in HPA with Al-T = 0.2 mol L-1 and optimal hydrolysis ratios (B) (ca. 2.3-2.4). But the content of Al-30 becomes higher than that of Al-13 when the HPA solution is heated at 95 degrees C for more than 12 h. Al-30 becomes the dominant nanosized At species in HPA, and its content reaches 76.8% in sample with Al-T = 0.2 mol L-1 and B = 2.4. Although Al-30 is more stable than Al-13, it is also a metastable species during the process of At hydrolysis, polymerization and precipitation. The decomposition and polymerization of Al-30 are also speed up by increase the heating temperature. The optimal preparation temperature of Al-30 is ca. 95 degrees C. At species in HPA solutions transform into more stable and inert species through inter-species polymerization and intra-species structure rearrangement upon thermal treatment. So Al-b Contents decrease, and Al. contents increase. Al-30 cannot react with Ferron within 120 min, and it is classified as Al-c species in Al-Ferron analysis. The effect of thermal treatment on Al speciation in HPA solutions with different total At concentration and B value were also investigated. (c) 2006 Elsevier B.V. All rights reserved.