Uptake of various cations by amorphous BaAl 2Si 2O 8 prepared by solid-state reaction of kaolin with BaCO 3

Abstract

The uptake of various ions by amorphous and crystalline BaAl 2Si 2O 8 was investigated. The BaAl 2Si 2O 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 2Si 2O 8 sample than crystalline BaAl 2Si 2O 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 29Si and 27Al 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.