Determination of Monomeric and Polynuclear Aluminum(III) Species and Hydrolysis Constants

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Abstract
Aqueous reactions of aluminum(III) were investigated in acidic aluminum solutions at fixed ionic strength and below the pH of precipitation. Computer analysis of potentiometric data for three concentrations (0.1, 0.5, and 1 mM Al) indicated that the experimental results could be explained by assuming only two principal hydrolyzed species, AlOH2+ and Al8(OH)4+ 20. No other combination of aluminum complexes appeared to fit the data as did these species. The equilibrium constant for the monohydroxy ion was very close to values determined by other methods. The refined values of the formation constants for ∗pK 1 and pβ8,20 were 5.55 and 68.7, respectively, at an ionic strength of 0.15, and 5.11 and 64.1, respectively, at zero ionic strength.