Interaction between Al³⁺ and Acrylic Acid and Polyacrylic Acid in Acidic Aqueous Solution: A Model Experiment for the Behavior of Al³⁺ in Acidified Soil Solution

Abstract

From the viewpoint of the phytotoxicity and mobility of Al³⁺ released from soil minerals due to soil acidification, the interaction between Al³⁺ and acrylic acid (AA) and polyacrylic acid (PAA) as a model compound of fulvic acid was investigated. The interaction was examined at pH 3 so as to avoid the hydrolysis of Al³⁺. The interaction between Al³⁺ and AA was weak. However, the interaction between Al³⁺ and PAA was strong and depended on the initial (COOH in PAA)/Al molar ratio (R_P) of the solution. For the range of 1/R_P, the interaction between Al³⁺ and PAA can be divided into three categories: (1) 1:1 Al-PAA-complex (an Al³⁺ combines to a carboxyl group), (2) intermolecular Al-PAA-complex (an Al³⁺ combines to more than 2 carboxyl groups of other Al-PAA-complexes) in addition to the 1:1 Al-PAA-complex and (3) precipitation of intermolecular complexes. In conclusion, R_P is an important factor affecting the behavior of Al³⁺ in acidic soil solution.