Lanthanum modification of crystalline phases and residual glass in augite glass ceramics produced with industrial solid wastes

Abstract The effects of La2O3 on microstructure and properties of the CaO-MgO-SiO2-Al2O3 glass ceramics, made from Bayan Obo West Mine tailing and fly ash, were investigated. Results showed that La2O3 additions up to 2 wt% promoted augite crystallization. Above this concentration, La2O3 suppressed augite crystallization by rather forming lanthanum oxyapatite that acted as a barrier for the growth of augite. Also Cr ions, the key element for the augite nuclei, were enriched in lanthanum oxyapatite. The La3+ cations were found to partially substitute for Ca2+ at the M2 structural sites in clinopyroxene (augite). Nano crystalline clusters, containing La3+, Na+, Ca2+, Mg2+ and Fe3+ in augite-like proportions, were found uniformly dispersed in the residual glassy phase. The glass ceramic with 2 wt% La2O3 shows optimum mechanical properties and chemical durability. The bending strength and Vickers hardness are 238 MPa and 7.57 GPa, acid and alkali-resistance are 97.5% and 98.9%, respectively.