Preparation and simultaneous ion uptake properties of CaO-Fe2O3-SiO2 compounds

CaO-Fe2O3-SiO2 (CFS) compounds were prepared from mixtures of Ca(OH)2, FeOOH and SiO2 and their simultaneous uptake properties for cations and anions were investigated. The starting powders were mixed in various ratios using a planetary ball mill and heated at various temperatures in air and flowing N2 atmospheres. Amorphous compounds were formed by heating up to < 600 C while haematite (alpha-Fe2O3) was crystallised at 600 C and above and calcium silicates and/or calcium iron silicates at 800 C and above. Simultaneous ion uptake experiments were carried out by a batch method using solutions containing the same concentrations of Ni2+, NH4(+) and H2PO4(-). The samples heated at 600 C showed the highest ion uptake ability. The uptake abilities were higher for Ni2+ and H2PO4(-) than for NH4(+) and increased with increasing CaO content in the CFSs. The uptake abilities for the three ions were enhanced by heating the samples in flowing N2. The simultaneous uptake mechanisms are thought to be similar to those observed in the CAS compounds, i.e. ligand change (Ca2+ to Ni2+), compound precipitation and adsorption. The CFS compounds with the following advantages compared well with CaO-Al2O3-SiO2 (CAS): higher uptake ability for phosphate ions; and easy separation of a contaminated sorbent from the solution after uptake using a magnet. 14 refs.