Enhanced lithium extraction from α-spodumene with fluorine-based chemical method: A stepwise heat treatment for fluorine removal

Abstract

Fluorine (F) additives could enhance lithium (Li) extraction from α-spodumene without phase transformation (typically at ∼ 1100 °C). Fluorine additives participated in the destruction of the crystal structure of α-spodumene by forming HF with sulfuric acid. The sulfuric acid was employed to catalyze the destruction of the α-spodumene crystal structure and convert insoluble fluorides to sulfates. Residual fluorine mainly existed as HF/F- and a samll amount of AlFx after acid pre-leaching. Based on different boiling points of HF-H2O and H2SO4-H2O systems, a stepwise heat treatment was proposed herein to recycle F and avoid lithium loss caused by coordination with F. A systematical investigation of effects of different factors such as heating temperature (200–350 °C), heating time (3–12 h), initial ratio of ore/H2SO4 (1:1, 1:2 g/mL) and different heating style (directly or stepwise) on F removal was conducted. The results indicated that only 2.03% of F remained in the leaching solution after the stepwise heat treatment for an ore/HF/H2SO4 ratio of 1:3:2 g/mL/mL at 120 °C for 3 h and 250 °C for 3 h. About 93.73% of Li and 73.14% of Al were extracted during this stepwise heat treatment. More importantly, premiliary separation of Li and Al was realized due to the formation of acid insoluble Al2(SO4)3, which was conducive to the subsequent separation and purification of lithium production.