Analytical Sciences

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

Mayumi ETOU,*1 Yuka MASAKI,*1 Yutaka TSUJI,*2 Tomoyuki SAITO,*1 Shuqin BAI,*3 Ikuko NISHIDA,*4 Yoshihiro OKAUE,*1 and Takushi YOKOYAMA*1

*1 Department of Chemistry, Faculty of Science, Kyushu University, 6-10-1 Hakozaki, Higashi, Fukuoka 812-8581, Japan
*2 Kurume National College of Technology, Komorino, Kurume, Fukuoka 830-8555, Japan
*3 College of Environment and Resources, Inner Mongolia University, No. 235 West University Road, Saihan, Huhhot 010021, P. R. China
*4 Kurita Water Industries Ltd., 1-1 Gochoyama, Kawada, Nogi, Shimotsuga, Tochigi 329-0105, Japan

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.

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