Hydrothermal synthesis of mixtures of NaA zeolite and sodalite from Ti-bearing electric arc furnace slag

Abstract

Ti-bearing electric arc furnace slag (Ti-bearing EAF slag) is the main solid waste generated in the direct reduction iron making process. During the extraction process of Ti from Ti-bearing EAF slag, a by-product containing abundant Si and Al was seldom utilized, thus leading to waste of valuable elements and secondary pollution. In this paper, NaA zeolite (6Na₂O·6Al₂O₃·12SiO₂) and sodalite (SOD, 4Na₂O·3Al₂O₃·6SiO₂) were synthesized successfully using the by-product as a precursor. The effects of the SiO₂/Al₂O₃ molar ratio (n(SiO₂)/n(Al₂O₃)), H₂O/Na₂O molar ratio (n(H₂O)/n(Na₂O)), hydrothermal temperature and time on the crystal phase and microstructure of the prepared zeolites were systematically investigated. The results indicated that NaA zeolite with good crystallinity and cubic morphology was obtained at 140 °C for 3 h with n(SiO₂)/n(Al₂O₃) and n(H₂O)/n(Na₂O) fixed at 2.0 : 1 and 100 : 1, respectively. Decreasing n(H₂O)/n(Na₂O), raising the hydrothermal temperature and prolonging the hydrothermal time were beneficial for the formation of spherical SOD zeolite. The phase transformation between NaA and SOD zeolite was discussed and a mechanism was proposed to explain the phenomenon of these zeolites coexisting in the obtained samples. In addition, the removal performances of Cu²⁺ in aqueous solutions using zeolites synthesized at different temperatures were studied. The maximum removal capacity of the prepared zeolite can reach 1.346 mmol g⁻¹ for 180 min.