Chemical species of Al in a gypsum-treated Kitakami Andosol: Direct analysis of Al adsorbed on cation exchange resin using²⁷Al NMR

To examine the possibility that the Al₁₃ polymer ([A10₄Al₁₂(OH)24(H₂0)₁₂]⁷⁺) could be formed in soils after gypsum application, an analytical method using a cation exchange resin and²⁷Al nuclear magnetic resonance (NMR) spectroscopy was applied to gypsum-treated Kitakami Andosol (fine, mixed, mesic, Andic Dystrochrept). The NMR spectra of the cation exchange resins which retained artificially synthesized hydroxy-AI, showed two broad peaks at 0 and 63 ppm. These results indicated that monomer and/or dimer Al and Al¹³ polymers adsorbed on the cation exchange resin could be detected with²⁷Al NMR. The amount of polymer Al increased by gypsum application in the Kitakami soil. The NMR spectrum of this resin showed only one peak at 0 ppm indicating that the polymer Al formed in the gypsum treated Kitakami soil was not the Al¹³ polymer.