Direct Preparation of Water-Soluble Lithium Salts from α-Spodumene by Roasting with Different Sulfates

The conventional process of lithium extraction from α-spodumene requires high-temperature calcination to transform α-spodumene into β-spodumene, and concentrated acid roasting followed by water leaching. This study proposed the direct preparation of water-soluble lithium salts from α-spodumene by roasting with different sulfates to avoid the use of concentrated acid and simplify the process flow. In this study, the theoretical feasibilities of the roasting of α-LiAlSi2O6 with different sulfates to produce water-soluble lithium salts were first verified using HSC Chemistry 10. Then, the roasting of spodumene concentrate with CaSO4·2H2O, MgSO4·7H2O, and Na2SO4 followed by water leaching was investigated to extract lithium from α-spodumene. The complete transformation from α-spodumene to γ- and β-spodumene without additives occurred at 1000 °C for 30 min. CaSO4·2H2O did not significantly promote the phase transformation or the reaction with α-spodumene. MgSO4·7H2O and Na2SO4 could react with α-spodumene to generate water-soluble Li2Mg2(SO4)3 and LiNaSO4, respectively, but the roasting results with Na2SO4 were better than MgSO4·7H2O. Here, 93.8% Li was converted into LiNaSO4 when roasting with Na2SO4 at 1000 °C for 60 min with an ore/Na2SO4 mass ratio of 1:0.7. Low-temperature roasting of the concentrate with Na2SO4 and CaO was proposed to produce LiNaSO4 at 850–875 °C for 60 min with ore/Na2SO4/CaO mass ratios of 1:0.7:(0.05 to 0.1), and the lithium extraction efficiencies were about 86%.