Preparation and simultaneous ion uptake properties of CaO-Fe ₂O₃-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 hematite (α-Fe₂O₃) was crystallized at >600°C and calcium silicates and/or calcium iron silicates at >800°C. Simultaneous ion uptake experiments were carried out by a batch method using solutions containing 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 NH ₄⁺ and increased with increasing CaO content in the CFSs. The uptake abilities for three ions 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⁺→ Ni²⁺), compound precipitation and adsorption. The CFS compounds have the following advantages compared with CaO-Al₂O₃-SiO ₂ (CAS) ; (1) higher uptake ability for phosphate ions (a model for harmful oxyanions) and (2) easy separatton of a contaminated sortent from the solution after uptake using a magnet.