Abstract
This work aims to determine the influence of amorphous SiO2 on the formation of katoite, on the formation of mayenite, and on its adsorption capacity for Cu2+ ions. Katoite was synthesised under hydrothermal conditions (130°C; 4 h) in the primary mixture, which consisted of amorphous SiO2, aluminium oxide and calcium oxide. It has been found that, at 350°C in the pure system, katoite completely recrystallised into a mixture of mayenite and portlandite. Moreover, in the presence of the SiO2 additive, calcination at 350°C yielded the same products once calcium monocarboaluminate and katoite substituted with Si4+ ions had fully decomposed. It was also observed that MA-Si3 exhibited slightly better adsorption properties for Cu2+ ions than MA3: after 60 min, its adsorption capacities were 196.3 and 194.5 mg/g, respectively. It was determined that in the MA1 sample, a similar intensity of calcite, vaterite and aragonite was formed. Additionally, traces of calcium monocarboaluminate, rouaite and gibbsite were identified in the XRD patterns. Also, more intensive diffraction peaks of calcite were formed in the MA3 sample than in the MA1 and MA-Si1 samples. Moreover, higher intensity diffraction peaks characteristic of katoite formed in the MA-Si3 sample.