Hybrid experimental-DFT studies on sustainable production of nepheline ceramics from hazardous spent potlining residues

An advanced mechanochemical-thermal protocol for nepheline (NaAlSiO 4 ) synthesis has been engineered through the valorization of spent potlining (SPL), a hazardous aluminium electrolysis residue, as a low-cost aluminosilicate precursor, synergized with Na 2 CO 3 as a reactive flux. High-temperature roasting (875–1000 °C, 1.5 h) coupled with aqueous leaching facilitated SPL-Na 2 CO 3 dissociation into phase-pure NaAlSiO 4 , with optimal conversion efficiency (100 % phase purity) achieved at 46wt% Na 2 CO 3 and 1000 °C, as corroborated by solid-state reaction kinetics and thermodynamic modelling (ΔG, K) via HSC Chemistry 6.0. Mechanistic elucidation via DFT simulations (DMol3, BIOVIA) revealed Na 2 CO 3 -mediated fluorinated phase (Na 3 AlF 6 ) decomposition to NaAlO 2 , followed by Al 2 Si 2 O 7 aluminosilicate restructuring into NaAlSiO 4 . Electronic structure analyses (HOMO-LUMO, DOS) yielded bandgaps of 2.23eV (NaAlO 2 ) and 4.18eV (NaAlSiO 4 ), with the latter's wide bandgap indicative of UV-B photon absorption (λ ≤ 296nm), corroborated by optoelectronic characterization. Multimodal characterization (XRD, XRF crystallography, SEM-EDS microstructural mapping, IC ion quantification) validated stoichiometric fidelity and phase homogeneity, establishing this SPL-derived route as a scalable, waste-to-functional-material strategy for advanced ceramics and sustainable critical mineral recovery. The larger band gap of 4.18eV reveals that NaAlSiO 4 required higher photon energy for electron excitation, positioning the compound a promising material for Ultraviolet-based applications.