Kinetics of leaching lithium from α-spodumene in enhanced acid treatment using HF/H2SO4 as medium

Abstract

Abstract An enhanced leaching of Li from α-spodumene was carried out using a mixture of hydrofluoric and sulfuric acid (HF/H2SO4) as the medium. Based on the optimized leaching conditions, the leaching kinetics of Li was investigated in an ore/HF/H2SO4 ratio of 1:3:2 g:mL:mL with leaching temperature ranging from 50 to 100 °C. The results indicate that the leaching kinetics of Li fitted well with a model based on the shrinking core model. In addition, the leaching rate of Li was controlled by chemical reactions and diffusion through the product layers. The apparent activation energy Ea was calculated to be 32.68 kJ/mol. Solid films were formed because of the generation of insoluble products such as cryolithionite (Na3Li2Al2F12), cryolite (Na3AlF6), calcium fluoride (CaF2), potassium cryolite (K2AlF5), aluminum fluoride (AlF3), and fluorosilicates (Na2SiF6 or KNaSiF6). Furthermore, the effects of the ore/HF ratio and leaching temperature on the leaching behavior of Li, Al and Si were investigated. The results indicate that the ore/HF ratio and leaching temperature could clearly affect the distribution of HF molecules on the leaching of Li, Al and Si, which are important for the selective leaching of Li over Al and Si with this fluorine-based chemical method.