Speciation of Hydroxyaluminosilicate and Hydroxyaluminum Ions as Affected by the Presence of Montmorillonite : Extraction Experiment with Potassium Chloride and Speciation by ^<27>Al-NMR

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The changes of Al species in the presence of montmorillonite (Mt) with aging were investigated using ^2Al-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 Al_<13> ([AlO_4Al_<12>(OH)_<24>(H_2O)_<12>]^<7+>) in the HAS solution with a Si/Al molar ratio of 0.09 and hydroxyaluminum (HyA) solution decreased during 42d of aging, suggesting that degradation (or polymerization) of Al_<13> took place upon aging. In the presence of Mt, Al_<13> was adsorbed onto Mt from the HyA and HAS (0.09) solutions. The adsorbed Al_<13> 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 Al_<13> was exchangeable and the rest was considerably stabilized by adsorption onto Mt. The desorption ratios of Al from the HyA- and HAS(0.09)-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 Al_<13> and Al_<NON>. The Al_<NON> was attributed to electrically asymmetric Al including HAS and/or polymer HyA ions.
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