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
Experimental Reagents and sample solutions Aluminum (Al) stock solutions (0.1 and 1.0 mol dm -3 ) were prepared by dissolving crystalline aluminum nitrate nonahydrate (Al(NO3)3·9H2O, Wako Pure Chemicals) in 0.1 mol dm -3 nitric acid. The Al concentration was determined by EDTA titration. Acrylic acid (AA) solutions with the desired concentrations were prepared by diluting liquid acrylic acid (Wako Pure Chemicals) with ultrapure water (Milli-Q SP system, Millipore). On the other hand,
... er hand, polyacrylic acid (PAA) solutions with desired 2011 From the viewpoint of the phytotoxicity and mobility of Al 3+ released from soil minerals due to soil acidification, the interaction between Al 3+ 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 Al 3+ . The interaction between Al 3+ and AA was weak. However, the interaction between Al 3+ and PAA was strong and depended on the initial (COOH in PAA)/Al molar ratio (RP) of the solution. For the range of 1/RP, the interaction between Al 3+ and PAA can be divided into three categories: (1) 1:1 Al-PAA-complex (an Al 3+ combines to a carboxyl group), (2) intermolecular Al-PAA-complex (an Al 3+ 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, RP is an important factor affecting the behavior of Al 3+ in acidic soil solution.