The uptake of various ions by amorphous and crystalline CaAl2Si2O8 was investigated. The CaAl2Si2O8 samples were prepared by solid-state reaction of kaolinite with CaCO3, ground for 0-24 h and fired at 600-1000°C for 24 h. Uptake experiments were performed both at room temperature (25°C) and 60°C at a solid:solution ratio of 0.002 g ml°1 with cation concentrations ranging from 10-4-10-2 M. The cations examined were alkali ions (Na+ and K+), alkaline earth ions (Mg2+, Sr2+ and Ba2+) and transition metal ions (Ni2+, Co2+, Cu2+ and Zn2+). The uptake of transition metal ions by amorphous CaAl2Si2O8 was found to be higher than by crystalline CaAl2Si2O8. The uptake of transition metal ions by amorphous CaAl2Si2O8 was higher than the uptake of alkali and alkaline earth ions, indicating a high selectivity for transition metal ion and their uptake was further enhanced at higher solution temperatures. Uptake of the various ions showed strong pH dependence and indicated high uptake ability at neutral pH. For the heavy metal ions the uptake selectivity was found to be Cu > Zn > Ni ≥ Co, suggesting a correlation with their ion products. The effectiveness of amorphous CaAl2Si2O8 as an uptake agent for heavy metal ions was confirmed by experiments with real river water.
ASJC Scopus subject areas
- Materials Chemistry