Uptake properties of Ni2+ by nCaO·Al2O3·2SiO2 (n = 1-4) prepared from solid-state reaction of kaolinite and calcite

A series of nCaO·Al2O3·2SiO2 samples (n = 1-4) were prepared by solid-state reaction of mechanochemically treated mixtures of kaolinite and calcite fired at 600-1000 °C for 24 h. All the samples were X-ray amorphous after firing at 600-800 °C but had crystallized by 900 °C. The main crystalline phases were anorthite (n = 1), gehlenite (n = 2 and 3) and larnite (n = 4). The uptake of Ni2+ by nCaO·Al2O3·2SiO2 samples fired at 800 and 900 °C was investigated at room temperature using solutions with initial Ni2+ concentrations of 0.1-50 mmol/l. Amorphous samples (fired at 800 °C) showed a higher Ni2+ uptake capacity than crystalline samples (fired at 900 °C). Ni2+ uptake was found to increase with increasing of CaO content. Amorphous 4CaO·Al2O3·2SiO2 showed the highest Ni2+ uptake capacity (about 9 mmol/g). The Ni2+ uptake abilities of the present samples are higher than those of other materials reported in the literature. Since the sorbed Ni2+/released Ca2+ ratios of these samples are close to unity, ion replacement of Ni2+ for Ca2+ is thought to be the principal mechanism of Ni2+ uptake by the present samples.