title: Effects of low temperature on aluminum(III) hydrolysis: theoretical and experimental studies.
abstract: In this study, the effects 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 degrees C were calculated from that at 25 degrees 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 degrees 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 degrees C, Al13 was the dominant species in a pH range of 4.0 to 4.5, whereas at 4 degrees C, All3 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 degrees C in comparison with the range of 0.5 pH unit at 25 degrees C.
authors.affiliation: Department of Civil Engineering, Hong Kong University of Science and Technology, Clear Water Bay, Kowloon 999077, Hong Kong, China. cexiao@ust.hk
authors.forename: Feng
authors.initials: F
authors.lastname: Xiao
authors.forename: Baojie
authors.initials: B
authors.lastname: Zhang
authors.forename: Chery
authors.initials: C
authors.lastname: Lee
mesh_terms: D000535:Aluminum / Q000737:chemistry*; D003080:Cold Temperature; D006863:Hydrogen-Ion Concentration; D006868:Hydrolysis; D009682:Magnetic Resonance Spectroscopy / Q000379:methods; D012995:Solubility; D013054:Spectrophotometry, Atomic / Q000379:methods; D018508:Water Purification / Q000379:methods*
chemical_list: D000535:Aluminum