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-LiAlSi 2 O 6 with different sulfates to produce water-soluble lithium salts were first verified using HSC Chemistry 10. Then, the roasting of spodumene concentrate with CaSO 4 ·2H 2 O, MgSO 4 ·7H 2 O, and Na 2 SO 4 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. CaSO 4 ·2H 2 O did not significantly promote the phase transformation or the reaction with α-spodumene. MgSO 4 ·7H 2 O and Na 2 SO 4 could react with α-spodumene to generate water-soluble Li 2 Mg 2 (SO 4 ) 3 and LiNaSO 4, respectively, but the roasting results with Na 2 SO 4 were better than MgSO 4 ·7H 2 O. Here, 93.8% Li was converted into LiNaSO 4 when roasting with Na 2 SO 4 at 1000 °C for 60 min with an ore/Na 2 SO 4 mass ratio of 1:0.7. Low-temperature roasting of the concentrate with Na 2 SO 4 and CaO was proposed to produce LiNaSO 4 at 850–875 °C for 60 min with ore/Na 2 SO 4 /CaO mass ratios of 1:0.7:(0.05 to 0.1), and the lithium extraction efficiencies were about 86%.