Interaction between Al³⁺ and Poly(acrylic acid) (PAA) in Aqueous Solution—Formation Modes for the Al–PAA Complexes

Abstract

The interaction between Al 3 and poly(acrylic acid) (PAA) which is a polyelectrolyte was investigated under various conditions. It was revealed that PAA has a strong binding ability with Al 3 not only in liquid phase but also in solid phase. Even when no hydrolysis of Al 3 occur at pH 3, the Al 3 was deposited together with PAA under various COOH/Al ratios and formed an insoluble Al-PAA complex. It was found that the hydrolysis of Al 3 was strongly retarded due to the complexation with PAA even under neutral and alkaline conditions. An excess amount of PAA in mixed solution retarded the precipitation of Al 3 at pH 4.5-8. The soluble Al-PAA complex suppressed the formation of the Al 13 polycation in solution. Moreover, an insoluble Al-PAA complex was also formed under COOH/Al ratio of 1. The molar ratio of COOH/Al in precipitates was dependent on the pH of the reaction solution. The type of chemical bond involved in the Al-PAA complex was a ected by the Al 3 hydrolysis and dissociation of H from the carboxyl groups in PAA. At pH 3, one Al 3 combined with three carboxyl groups by substitution reaction with H . Above pH 3, one Al(OH) 2 or one Al(OH) 2 combined ionically with two or one COO groups, respectively. The results of this study can be potentially applied to formulate a method to remove Al 3 from various wastewater environments in a wide pH range.