Conversion from α-spodumene to intermediate product Li2SiO3 by hydrothermal alkaline treatment in the lithium extraction process

Abstract

The key to the lithium extraction from α-spodumene is destroying the crystal structure. The conventional commercial process requires high-temperature calcination to transform α-spodumene into β-spodumene. This study aimed at finding an alternative treatment for destroying the structure of α-spodumene and extracting the lithium. The results indicated that α-spodumene could be directly decomposed by NaOH solution and the Li element in α-spodumene was converted into intermediate product Li2SiO3 in the form of solid phase under certain conditions. According to the experiments, the possible reactions during the hydrothermal alkaline treatment were predicted, which were thermodynamically possible by the calculation of Gibbs free energy using HSC Chemistry 10. The total extraction efficiency of Li2O was 87.3%, including the extraction efficiency of Li2O leached into liquid phase, 7.6%, and converted into Li2SiO3, 79.7%, obtained under optimal conditions: stirring speed of 500 rpm, leaching temperature of 250 °C, mass ratio of NaOH/ore of 1.5, initial NaOH concentration of 25 wt%, and leaching time of 24 h. Then the Li element in the Li2SiO3 could be extracted by acid leaching and precipitated using Na2CO3. The mother liquor obtained after hydrothermal alkaline treatment was reused for the subsequent hydrothermal alkaline cyclic leaching under the above conditions. During three cycles of alkaline treatment, the α-spodumene decomposition was stable, and the total Li2O extraction efficiency was around 86% (∼84% was converted into Li2SiO3). This process avoids high-temperature calcination and concentrated acid roasting, where the acid leaching process is carried out at room temperature.