Speciation of hydroxyaluminosilicate and hydroxyaluminum ions as affected by the presence of montmorillonite: Extraction experiment with potassium chloride and speciation by 27Al-NMR

Abstract

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 AlNON. The AlNON was attributed to electrically asymmetric Al including HAS and/or polymer HyA ions.