Direct Extraction of Lithium from α-Spodumene by Salt Roasting-Leaching Process

In recent years, several methods have been reported to extract lithium (Li) from spodumene. However, the majority of them still require the transformation of the naturally occurring spodumene phase (α) to the more reactive crystalline phase (β) by calcination at 1100 °C. To address the economic drawbacks and high greenhouse gas emission of this phase transformation, this study aimed to directly extract Li from α-spodumene. Nine reagents of alkali metals (Group IA), alkaline earth metals (Group IIA), and ammonium (NH₄⁺) salts were examined for roasting and phase transformation of α-spodumene to water- or acid-soluble phases. For this purpose, sequential roasting, water leaching, and acid leaching were performed. The leaching recovery results showed that the order of roasting efficacy of the three reagent categories is Group IA > Group IIA > > NH₄⁺. 71 and 88% of water leaching and total leaching recovery values, correspondingly, were achieved by the NaOH roasting-water leaching-acid leaching process, under the nonoptimized conditions of a roasting temperature of 320 °C, an NaOH: spodumene ratio of 1.5:1, and a roasting time of 2 h. Thermodynamics analysis by FactSage demonstrated that α-spodumene was decomposed to Na₂SiO₃, Na₄SiO₄, NaAlO₂, and Li₃NaSiO₄by NaOH and to NaAlSiO₄, Na₂SiO₃, and Li₃NaSiO₄by Na₂CO₃. Eh-pH diagrams calculated by HSC Chemistry revealed that despite the low solubility of lithium silicates in water, they dissolve at high pH (>12.5), explaining the high water leaching recovery of Li. In future studies, the optimization of the process parameters will be conducted to maximize the Li recovery in water leaching, while recovering other valuable elements as byproducts.