Investigation of Enhanced Leaching of Lithium from α-Spodumene Using Hydrofluoric and Sulfuric Acid

An effective method using hydrofluoric and sulfuric acid was proposed to enhance the leaching of lithium from alpha-spodumene, without calcination that is subjected to 1000 degrees C for phase transformation. The thermodynamic feasibility of the reactions was firstly verified. Dissolution conditions were tested to maximize the leaching efficiency of lithium and with efficient utilization of hydrofluoric acid (HF) served as evaluation criteria. The results showed that 96% of lithium could be transferred into lixivium with an ore/HF/H2SO4 ratio of 1:3:2 (g/mL/mL), at 100 degrees C for 3 h. Due to the fact that HF molecules were the main reaction form, the dissolution behaviors were theoretically represented and investigated by dissolution in HF/H2SO4. When combined with chemical elements analyses and characterizations, the results of the dissolution behaviors revealed that -spodumene and albite were preferentially dissolved over quartz. Insoluble fluoroaluminates, such as AlF3, cryolite (Na3AlF6) and cryolithionite (Na3Li3Al2F12), were generated and might be further partially dissolved by H2SO4. Fluorosilicates, such as K2SiF6, Na2SiF6, or KNaSiF6, were also generated as a part of the insoluble residues. This work provides fundamental insight into the role of HF/H2SO4 played in the dissolution of alpha-spodumene, and sheds light on a novel and promising process to efficiently extract lithium.