Speciation of hydroxyaluminosilicate and hydroxyaluminum ions as affected by the presence of montmorillonite: Extraction experiment with potassium chloride and speciation by²⁷Al-NMR

The changes of Al species in the presence of montmorillonite (Mt) with aging were investigated using 27Al-nuclear magnetic resonance and inductively coupled plasma atomic emission spectroscopy after extraction with 1 mol L^-1 KCl. Composition of the Al species in a hydroxyaluminosilicate (HAS) solution with a Si/Al molar ratio of 0.63 without Mt was not appreciably affected by 42 d of aging. In the absence of Mt, the concentration of Al13 ([Al0₄Al¹²(OH)₂₄- H₂O)₁₂]₇₊) in the HAS solution with a Si/Al molar ratio of 0.09 and hydroxy-aluminum (HyA) solution decreased during 42 d of aging, suggesting that degradation (or polymerization) of Al13 took place upon aging. In the presence of Mt, Al₁₃ was adsorbed onto Mt from the HyA and HAS(0.09) solutions. The adsorbed Al₁₃ was partly recovered by 1 mol L_-1 KCl from HyA- and HAS(0.09)Mt complexes after 42 d of aging, suggesting that at least a part of the adsorbed Al₁₃ was exchangeable and the rest was considerably stabilized by adsorption onto Mt. The desorption ratios of Al from the HyA- and HAS(O.09)Mt complexes accounted for 25 to 30% and 6 to 8% of total Al adsorbed, respectively. The species of Al desorbed from these complexes consisted mainly of Al₁₃ and Al_NON. The Al_NON was attributed to electrically asymmetric Al including HAS and/or polymer HyA ions.