Alkali-Induced Phase Transition to β-Spodumene along the LiAlSi2O6-LiAlSi4O10 Join

Abstract

Due to the refractory nature of α-spodumene (LiAlSi2O6) and petalite (LiAlSi4O10), two major lithium minerals, conventional lithium recovery processes involve a high-temperature pre-treatment (>1000 °C) to induce a phase transition to tetragonal β-spodumene, an open structure allowing easier access to lithium through ion exchange. Considering that these high temperatures are not dictated by thermodynamics but rather sluggish kinetics, the study investigates the mechanisms enhancing the rate of transformation to β-spodumene at lower temperatures while minimizing the growth of metastable hexagonal β-quartz typically observed at the onset of the conversion. The heat treatment of natural α-spodumene revealed that rapid growth of β-spodumene veinlets is achieved at ≤600 °C by activation of alkali-rich fluid inclusions, through a dissolution–recrystallization process. For petalite, the mechanism of the phase transition, initiated at ≈750 °C is a solid-state transformation keeping crystallographic coincidence with the mineral host. Synthetic growth experiments along the LiAlSi2O6-LiAlSi4O10 join indicate a compositional dependence on the resulting β-phase structure, where minor sodium doping strongly favors β-spodumene, as the tetrahedral framework of β-quartz does not allow the extent of deformation to accommodate the larger alkali. These findings open opportunities for energy-efficient lithium recovery pathways where the phase transition and ion exchange can be achieved simultaneously without a high-temperature pre-treatment.