Effects of low temperature on aluminum(III) hydrolysis: Theoretical andexperimental studies
XIAO Feng , ZHANG Baojie , LEE Chery
DOI:
Received October 08, 2007,Revised November 23, 2007, Accepted , Available online
Volume 20,2008,Pages 907-914
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In this study, the e ects of low temperature on aluminum(III) (Al) hydrolysis were examined both theoretically and experimentally
by constructing a solubility diagram for amorphous aluminum hydroxide (Al(OH)3(am)) and a distribution diagram of hydrolyzed Al
species. First, thermodynamic data of Al species at 4°C were calculated from that at 25°C. A well confirmed polymeric Al species,
AlO4Al12(OH)24
7+(Al13), was involved in building the diagrams and, correspondingly, the non-linear simultaneous equations with 13
degrees were resolved. Secondly, polarized Zeeman atomic absorption spectrophotometry (AAS), 27Al nuclear magnetic resonance
(NMR) spectroscopy, and ferron-based spectrophotometry were applied for constructing the practical diagrams. The results show that
a decrease of temperature from 25 to 4°C caused the Al(OH)3(am) boundary on the solubility diagram to shift toward the alkaline side
by about 1.0 pH unit and the minimum solubility of Al(OH)3(am) to reduce by 1.0 log unit. The distribution diagram indicates that
the monomeric Al, Al13, and solid-phase Al(OH)3 were alternately the predominant species with the increase of pH value during Al
hydrolysis. At 25°C, Al13 was the dominant species in a pH range of 4.0 to 4.5, whereas at 4°C, Al13 was the leading species in a pH
range spaced from 4.5 to 6.3. The predominant species changed from the monomeric Al to the solid-phase Al(OH)3 over the range of
1.8 pH units at 4°C in comparison with the range of 0.5 pH unit at 25°C.
