Abstract
The growing demand for lithium has led to increased extraction of lithium from hard rock minerals, predominantly spodumene (LiAlSi2O6). Currently, spodumene processing relies on a combination of dense media separation followed by flotation to produce a spodumene concentrate. Spodumene flotation is challenging, as micas, feldspars, and other silicates will often report to the concentrate. The concentrate is then subjected to calcination at 1000 to 1100 °C to convert monoclinic α-spodumene into tetragonal β-spodumene, which facilitates leaching of the lithium by sulphuric acid. Calcination is energy-intensive and so it is preferable to recover lithium from α-spodumene. Roasting of α-spodumene concentrates with alkali salts at 300 to 400 °C has been studied, but such tests have focused on the treatment of high-grade concentrates containing greater than 90% α-spodumene. In this study, the thermodynamic feasibility of using lower grade spodumene concentrates containing impurities such as feldspars was evaluated using the equilibrium model in HSC Chemistry 6.1. The model simulates the roasting behavior and quantifies the influence of key process variables, including feldspar content and composition, alkali salt dosage, and temperature. It was found that the temperature had little effect on the equilibrium amount of lithium orthosilicate, which is amenable to water leaching. The addition of feldspars and silica were found to result in increased formation of potassium and sodium metasilicates and/or aluminates at the expense of potassium hydroxide and sodium orthosilicate. Lithium orthosilicate was found to convert to lithium metasilicate at higher feldspar or silica contents. This work provides a fundamental thermodynamic basis for determining appropriate feed specifications and operating conditions for the potential industrial deployment of alkali roasting for the recovery of lithium from low grade spodumene deposits.