Uptake properties of Ni 2+ by nCaO·Al 2O 3·2SiO 2 ( n = 1–4) prepared from solid-state reaction of kaolinite and calcite

Abstract

A series of nCaO·Al 2O 3·2SiO 2 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 Ni 2+ by nCaO·Al 2O 3·2SiO 2 samples fired at 800 and 900 °C was investigated at room temperature using solutions with initial Ni 2+ concentrations of 0.1–50 mmol/l. Amorphous samples (fired at 800 °C) showed a higher Ni 2+ uptake capacity than crystalline samples (fired at 900 °C). Ni 2+ uptake was found to increase with increasing of CaO content. Amorphous 4CaO·Al 2O 3·2SiO 2 showed the highest Ni 2+ uptake capacity (about 9 mmol/g). The Ni 2+ uptake abilities of the present samples are higher than those of other materials reported in the literature. Since the sorbed Ni 2+/released Ca 2+ ratios of these samples are close to unity, ion replacement of Ni 2+ for Ca 2+ is thought to be the principal mechanism of Ni 2+ uptake by the present samples.