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The uptake of various ions by amorphous and crystalline BaAl 2 Si 2 O 8 was investigated. The BaAl 2 Si 2 O 8 samples were prepared by solid-state reaction of kaolin ground with BaCO 3 for periods from 1 to 24 h followed by firing at temperatures of 800–1200 °C for 24 h. Uptake experiments were performed at room temperature (25 °C) using a solid/solution ratio of 0.1 g/50 ml, with a cation concentration of 10 −3 M and reaction time of 24 h. The cations used for the uptake experiments were alkaline earth ions (Mg 2+ , Ca 2+ and Sr 2+ ) and transition metal ions (Ni 2+ , Co 2+ , Cu 2+ and Zn 2+ ). The uptake of alkaline earth ions was low in all the samples while the transition metal ion uptakes were higher in the amorphous BaAl 2 Si 2 O 8 sample than crystalline BaAl 2 Si 2 O 8 samples. The high uptake of transition metal ions by the amorphous sample was further enhanced by prolonging the grinding time. Since the amorphous sample appears from the 29 Si and 27 Al NMR spectra to have a similar local structure to crystalline hexacelsian (double-layered structure consisted of alternatively corner shared AlO 4 and SiO 4 tetrahedra), the uptake of transition metal ions is suggested to occur by release of interlayer Ba ions in the vicinity of edge sites with the adsorption of transition metal ions from the solution.

A comparison was made of the solid-state 29Si, 27Al and 43Ca MAS NMR spectra of the outer casing stone from Snefru's Bent Pyramid in Dahshour, Egypt, with two quarry limestones from the area. The NMR results suggest that the casing stones consist of limestone grains from the Tura quarry, cemented with an amorphous calcium-silicate gel formed by human intervention, by the addition of extra silica, possibly diatomaceous earth, from the Fayium area.

The influence of mechanochemical treatment on the homogeneity of gibbsite–silicic acid mixtures was investigated by 29 Si and 27 Al MAS NMR, DTA–TG and XRD. Increased homogeneity of mullite precursors prepared by grinding mixtures of the appropriate stoichiometry for 20 h is indicated by the appearance of metakaolinite-like 4-coordinated Al resonances in the 27 Al NMR spectra and new resonances at −93 and −101 ppm in the 29 Si spectra. The influence of hydration water on the grinding reactions is also discussed.