Forming zeolites and calcium silicate hydrates in Fe-rich, slag-based, porous inorganic polymers

Abstract

This study provides insights on the formation of crystalline phases from Fe-rich slag-based porous inorganic polymers (porous IPs), cured under hydrothermal conditions. The porous IPs were synthesised using synthetic slags with different chemistries (from FeO-SiO2-CaO to FeO-SiO2-Al2O3-CaO systems) as solid precursors, and a sodium silicate-based alkaline activator. Chemical expansion was used to create the porous structure. After hardening, the porous monoliths were hydrothermally processed at different temperatures and respective steam pressures (150 °C, 4.8 bar; 200 °C, 15.5 bar and 250 °C, 39.7 bar) and for different durations (12–18 h). The presence of aluminium promoted the formation of the zeolite analcime within the first 12 h. The formation of crystalline calcium-silicate hydrates was promoted after a longer curing duration; however, just after the formation of analcime had taken place. Next to these phases, the Fe-rich smectite nontronite and calcium carbonates were detected.